Chapter 16: Color Nodes

The Color menu provides an array of color filters that give you the option to perform multiple operations on an image within a single node (Color Correct), or to select a single-purpose node for each type of color adjustment (Brightness, e.g.), based on your needs and preference.

In This Chapter

Guidelines for Choosing the Right Color Node

Brightness Node

Channel Swap Node

Clamp Node

Color Correct Node

Color Curves Node

Colorspace Node

Contrast Node

F-Stops Node

Gamma Node

Hue Adjust Node

Indexed Color Node

Invert Node

Monochrome Node

Printer Lights Node

Tint Node

Video Safe Node

Guidelines for Choosing the Right Color Node

Some of the nodes in the Color menu perform a single, specific function. For example, the Video Safe node is used strictly to conform the colors of an image to television broadcast standards by converting "illegal" colors to video-safe colors. Similarly, the Monochrome node is used strictly to desaturate an image, Invert to invert color values, and so on.

The Color Curves node, on the other hand, which lets you manipulate color distribution curves directly, can be used to adjust brightness, contrast, color balance, and other image characteristics. When should you choose Color Curves rather than, say, a Brightness or Contrast node?

The answer will usually depend on the level of precision you need. Take, for example, an image that needs more contrast. The Contrast node is the fastest, easiest way to increase the contrast--just increase the parameter value. But if you need to increase contrast only in the shadows, and if you want the effect to fall off nonlinearly, use the Color Curves node instead, or the all-purpose Color Correct node, which is described next.

Swiss Army Node

In many cases, you may need to perform several types of color adjustment on an image, or you may need to experiment with several techniques until you get the result you want. This is when the Color Correct node is the best choice.

The Color Correct node is the "Swiss army knife" of color correction nodes--the functionality of most of the other color nodes is included in it. In fact, Color Correct is the most comprehensive and powerful color adjustment node in RAYZ. It can be used to make a single adjustment or as many types of adjustment as may be necessary for a particular image.

The parameters relevant to each operation are adjusted in a separate, selectable layer in the Color Correct Node Panel. You can turn off any layer temporarily and you can reorder the layers to change the order in which each adjustment is applied to the image. This node is the best choice when multiple types of correction are needed, or when you want to experiment.

In addition, the Color Correct node offers the "BCG" layer, in which brightness, contrast, and gamma values can be adjusted separately in the shadows, midtones, and highlights. You can even change the definition of shadows, mids, and highs to suit any image.

Computational Efficiency

RAYZ concatenates node operations and calculates them at floating point accuracy regardless of the bit depth of the image. Values are not clamped on node output, which means that it is not necessary to use the Color Correct node strictly to optimize multiple color correction operations and prevent data loss.

Note:

 

Certain operations, by their nature, are exceptions to the rule, such as Channel Swap and Monochrome. Whenever you add a node, or a Color Correct layer, of one of these types you could potentially lose some color data.

Self-Documenting Nodes

The single-purpose color nodes do offer the advantage of being "self-documenting." If you are examining a node network and you see a Brightness node, for example, you can immediately tell what type of operation is being performed.

With Color Correct, on the other hand, you would have to select the node and examine the layers in the Node Panel. However, you can always create an underlay for a Color Correct node and type a note that explains how it is being used. For more information about this feature of the Worksheet, see the section on Adding Underlays to the Worksheet in chapter 5.



Brightness Node

 Brightness node icon. The Brightness node is used to adjust the brightness of an image, or individual image channel. The node includes an Offset parameter that can be used to shift the distribution curve that defines the brightness of the output.

The Brightness node performs the following computation, where "V" represents the input value:

(V - Offset) * Brightness

The Brightness node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Note:

 

You can use the Color Curves Node when you need the increased precision afforded by manipulating brightness curves directly.

Adjusting Brightness

The Brightness parameter can be thought of as specifying the angle of a distribution curve that controls the remapping of values from the input image to the output--the higher the parameter value, the steeper the curve, and the brighter the output (and vice versa). This means that the rate of change is not even across the colorspace. Pixels with higher RGB values are affected more than the darkest pixels.

The Offset parameter , on the other hand, can be thought of as shifting the distribution curve back and forth across the input (horizontal) axis without changing its angle. The offset has the effect of increasing or decreasing pixel values evenly across the tonal range. Positive offset values shift the brightness curve down; negative offset values shift it up.

Image showing a graph of the brightness curve with and without an offset applied.

Fig. 16.1 Increasing the Brightness parameter affects the highest image values the most, while the Offset parameter affects the entire tonal range equally.

Brightness Parameters

Brightness

Each pixel in the input image is multiplied by the Brightness parameter value to get the corresponding output value, assuming an offset has not been specified.

The range of the Brightness slider is 0 to 2, although the upper end of the range is not constrained. The default value of 1.0 results in no change to the image, while values less than 1 decrease the brightness and values greater than 1 increase it.

If necessary, you can expand the parameter to access the channel controls, which work exactly like the master Brightness parameter but control each channel independently.

Offset

The Offset parameter value is subtracted from each pixel in the input image before it is multiplied by the Brightness parameter value. This means that a nonzero value in the Offset parameter will affect the output image even when the Brightness parameter is left at its default value.

Because the offset is subtracted from the pixel value,

Offset values are expressed by default in units based on the range of the input image colorspace: -255 to 255 for 8-bit; -65535 to 65535 for 16-bit; -1 to 1 for floating point. The default value is 0 (no offset), and the actual range of the parameter is unconstrained.

Tip:

 

The Offset values can always be displayed in floating point units by checking the Float Display option in the parameter Animation menu, which is located on the right side of the parameter's slider bar.

If necessary, you can expand the parameter to access the channel controls, which work exactly like the master Offset parameter but control each channel independently.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Channel Swap Node

 Channel Swap node icon. The Channel Swap node is used to redefine the channel assignments of the input(s). You can add channels, delete channels, swap channels, or fill a channel with black, white, or luminance.

The Channel Swap node accepts one or two inputs. The second, optional input enables you to combine channel data from two separate images in the output image:

Channel Swap Parameters

Image showing alpha channel reassignment in Channel Swap Node Panel.

Fig. 16.2 Channel Swap node with two inputs: Input 1 alpha channel is being replaced by the Input 2 alpha.

Channels Out

Use the Channels Out parameter to specify the number of channels the output image will contain, from one to 10 (the default is four channels). A channel menu will appear in the Swap parameter group for each output channel specified.

Luminance

The Luminance menu is used to specify the type of luminance to be calculated if you fill an output channel with luminance: Film, NTSC Video, or PAL Video. For the formulas used in the calculation, refer to Appendix A: How RAYZ Computes Luminance Values.

Swap

The Swap parameter group updates dynamically, based on the value you specify in the Channels Out parameter, to provide a menu for each channel of the output. Each Channel Swap menu lists all of the available input image channels, as well as Black, White, and Luminance. Just select the one you want to use for that output channel.

Most commonly, Channel Swap is used to add an alpha channel to an RGB image. You can select Black, White, or Luminance, or you can select any input channel you wish to use as the alpha. By connecting two nodes to Channel Swap, you can select the alpha channel from one input to use in the other.



Clamp Node

 Clamp node icon. The Clamp node is used to clamp the colorspace of an input image to the range you specify. All pixel values higher than the specified Max Value or lower than the specified Min Value are clamped; pixel values within the Clamp range are not changed by the node.

Clamp Parameters

Min Value

Use this parameter to set the minimum value of the output range. The default value is 0.

The master Min Value control adjusts all channels equally. To set the minimum value for a particular channel, expand the Min Value group to access the individual channel controls.

Max Value

Use this parameter to set the maximum value of the output range. The default value is 1 (which is equivalent to 255 in 8-bit; 65535 in 16-bit).

The master Max Value control adjusts all channels equally. To set the maximum value for a particular channel, expand the Max Value group to access the individual channel controls.



Color Correct Node

 Color Correct node icon. The Color Correct node is a comprehensive tool for performing a wide variety of adjustments. It provides a number of common color manipulation tools in one layer-based interface. The Color Correct node enables you to do any or all of the following:

The Color Correct node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Color Correct Parameters

In the Color Correct node, you create a separate layer for each type of adjustment you wish to make. Each layer features its own set of parameters, which you adjust to achieve the desired effect. You can add as many layers as you need, and any layer can be deleted, reordered, or temporarily disabled.

Adjustment Layer Buttons

Click any adjustment button in the Color Correct Node Panel to create a correction layer for that operation. You can expand any layer to access its parameters, which are described in the following sections covering each type of adjustment layer.

Image showing the Color Correct layer selector buttons, with each button labeled.

Fig. 16.3 Click one of the layer buttons to create a correction layer of that type.

Each layer includes a common set of controls to disable the layer temporarily, delete the layer, and reorder the layer in the Node Panel. For more information, see also Dynamic Parameter Groups in chapter 7.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.

BCG layer icon. BCG (Brightness, Contrast, Gamma) Layer

The BCG layer enables you to adjust Brightness, Contrast, and Gamma values and to set a Brightness Offset or Contrast Pivot.

For basic information about these operations, such as the formulas used to compute them and graphs illustrating the effect of an offset, refer to the descriptions of the individual nodes: Brightness Node, Contrast Node, and Gamma Node. The implementation of these operations in the BCG layer is described next.

Image showing a the contents of the BCG menu in the Color Correct node.

Fig. 16.4 The BCG menu is used to specify whether parameters apply to entire image (Master) or only to Shadows, Midtones, or Highlights.

BCG Menu

The Brightness, Contrast, Gamma, Offset, and Pivot parameters apply to whatever portion of the tonal range is currently selected in the BCG menu. By default, these parameters affect the entire tonal range of the image because the Master control is selected in the BCG menu; however, you can also select Shadows, Midtones, or Highlights.

This means, for example, that you can adjust the overall brightness level while Master is selected in the BCG menu, and then switch the menu to Shadows to further adjust the dark areas only.

BCG Parameters

All of the BCG parameter values are set by default at the value that represents no change from the input image, which for Brightness, Contrast, and Gamma is 1. Set any parameter by typing a value in the field or using the tuner to set the value. To adjust an individual image channel, expand the parameter to access the channel-level controls and adjust them in the same way as the image-level parameter.

Tone Range

The BCG layer provides a Tone Range graph in which you can define what tonal values should be considered shadows, midtones, or highlights and control the magnitude of the effect. Any adjustments you make to the BCG parameters in the Shadows, Midtones, and Highlights will apply to the range of values specified by the corresponding curve in the graph.

To use Tone Range, check the Shadows, Midtones, and/or Highlights boxes to display the curves for in the graph. Each curve can be adjusted by dragging a control point to reposition it. You can also add and delete points and apply different functions to the distribution curves, in the same way you would manipulate animation curves, as described in Chapter 8: Using the Curve Editor.

Image showing a graph of how changes to the BCG Range curve can be used to redefine the midtones.

Fig. 16.5 This example graphs the effect of reducing the range of values defined as Midtones and lowering the magnitude of any adjustment made to them.

Hue layer icon. Hue Adjust Layer

The Hue Adjust layer enables you to perform hue-based color adjustments using the HSV color model. This layer is identical to the Hue Adjust Node.

Hue

The Hue parameter provides a color wheel to rotate the color distribution vectors of the image around the axis of the colorspace; that is, to shift the hue. The inner circle of the wheel represents the input data.

You can perform the hue shift visually by dragging the color wheel, or you can type a value representing the degree of color shift into the Hue field. A value of 0 (or 360) represents no shift, while a value of 90, for example, would shift pure red (0) to green (90) and green to cyan (180).

Saturation

The Saturation parameter enables you to adjust the chrominance level in a range of 0 to 2, where the default value of 1 represents no change to the input image.

Value

The Value parameter enables you to adjust relative intensity, or brightness, in a range of 0 to 2. The default value of 1 represents no change, 0 will result in a black image, and 2 will result in "blown out" colors.

Curves layer icon. Curves Layer

The Curves layer enables you to modify the color attributes of an image by editing curves in a graph display. The horizontal axis of the graph represents the input values, and the vertical axis represents the output values to which they are mapped.

You can adjust the entire image using the Master curve, or any individual channel. To display a curve for editing, check the associated box: Master, Red, Green, Blue, Alpha, and/or Other.

The Curves layer in Color Correct is identical to the Color Curves node interface. Refer to the description of the Color Curves Node, which explains the use of color curves in more detail.

Mono layer icon. Monochrome Layer

The Monochrome layer is used to desaturate an image.

Amount

The Amount parameter specifies the level of desaturation, from 0 (no desaturation) to 1 (total). By default, the Monochrome layer totally desaturates the image.

Luminance

The Luminance menu is used to specify whether Film, NTSC, or PAL luminance should be used in the calculation. The formulas used are given in Appendix A: How RAYZ Computes Luminance Values.

Channel Swap layer button icon. Channel Swap Layer

This layer enables you to add or delete channels, swap channel values, or fill any channel with black, white, or luminance. It works exactly like the Channel Swap Node, with the exception that the Channel Swap node accepts a second input to be used when you want to swap channels between two different node images.

To use the Channel Swap layer, select the number of channels you want the output to have. Then use the menu that is automatically generated for each output channel to assign an input channel to it.

Contrast Stretch layer icon. Contrast Stretch Layer

The Contrast Stretch layer is used to change the contrast of an image or image channel by adjusting the minimum and maximum values that define the tonal range of the input or output colorspace.

You can type new values into the parameter fields or use the sliders to adjust the default values. You can also specify RGB values by expanding each parameter to access the individual channel controls, or by using the eyedropper tool associated with the parameter to sample an image pixel or pixel area in the Viewer.

Increasing Contrast: White and Black In

To increase the contrast of the image, decrease the range of the input colorspace by adjusting the input black (minimum) and white (maximum) values. The resulting smaller range of input values will be remapped to the larger output range, effectively expanding, or stretching, the input.

Decreasing Contrast: White and Black Out

To decrease the contrast of the image, decrease the range of the output colorspace by adjusting the output black (minimum) and white (maximum) values. The input values will be remapped to the smaller output range, effectively compressing the input.

Using the Contrast Stretch Eyedroppers

Set the Image Viewer's Source menu to Input Image to pick input image values. Then click the eyedropper tool for a parameter and use it to sample the image (see the description of the Color Picker Tools in chapter 14 if you need instructions):

Expand the parameter group to see the resulting values in the individual Red, Green, and Blue channel parameters, as the master parameter value is not modified when using the eyedropper.

Invert layer icon. Invert Layer

The Invert layer automatically inverts the color values of any or all channels in an image, effectively creating a negative of the image, by subtracting the current pixel value by the maximum pixel value.

The only parameter in the Invert layer is Channel Select , which is used to specify which channels should be inverted. The Channel Select parameter in the Invert layer works exactly like the node-level Channel Select parameter, but its settings apply only to the invert operation.

F-Stops layer icon. F-Stops Layer

The F-Stops layer enables you to adjust the exposure of an image using units equivalent to photographic stops. This layer is equivalent to using the F-Stops Node.

Increasing the F-Stops parameter value by one stop will double the values at each pixel. This effect is cumulative; bringing the value up two stops will increase the amount of light by a factor of four. Similarly, bringing it down one stop will reduce values by a factor of two.

Printer Lights layer icon. Printer Lights Layer

The Printer Lights layer enables you to control the exposure of an image using units that represent printer lights. This layer is equivalent to using the Printer Lights Node. The node description contains more detailed information on the operation.

Lights per Stop: This parameter specifies how many Printer Lights are equivalent to one full stop. This parameter should be set to match the rate used by the color lab being referenced, usually 8 or 6.

Lights: This parameter specifies the number of printer lights to use. The default value of 25 represents no change to the image.

The Lights and Lights per Stop parameters can be expanded to access parameters that adjust each channel individually.



Color Curves Node

 Color Curves node icon. The Color Curves Node Panel provides a graph in which you manipulate a curve that maps the color distribution from the input image to the output. This gives you more precise control than applying a single level of adjustment to all pixels equally.

The Color Curves node is commonly used to adjust contrast based on the tonal distribution of the input or to remove color casts by adjusting an individual color channel.

The Color Curves node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Manipulating Color Curves

The color curves are manipulated in the same way as animation curves in the RAYZ Curve Editor, except that the horizontal axis of the color curve graph represents the input colorspace instead of time. The vertical axis represents the output colorspace.

A row of checkboxes at the top of the graph in the Color Curves Node Panel controls which curves are displayed in the graph. The Master curve controls tonal values for the entire image, and the color channel curves control individual channel values.

Image showing the curve selection checkboxes in the Color Curves Node Panel.

Fig. 16.6 Color Curve selectors in the Node Panel.

The default curve is set to evenly map each input image value to the output image, resulting in no change to the image, as shown in Fig. 16.7.

Image showing graph of default master curve.

Fig. 16.7 The default curve is linear, with a control point at the minimum and maximum value for the colorspace.

Making Tonal Adjustments

The angle, or slope, of the curve affects how tonal values are redistributed. Color corrections can be made by repositioning the control points representing maximum and minimum. The examples in Fig. 16.8 provide some general guidelines.

Image showing graphs that illustrate various types of tonal corrections using the master color curve.

Fig. 16.8 Examples illustrating the effect of various modifications to color curves.

In many cases, however, you will want to take advantage of the additional precision offered by adding control points to a curve and by applying functions that specify a nonlinear distribution of values. You can add as many points as you want, and different functions can be applied to each curve segment.

Image showing graphs of color curve with added controls points and functions.

Fig. 16.9 Examples of color curves with control points and functions modifying the default (linear) curve.

Working with Points
Working with Curves

The functions in the popup menu are the same as those in the Curve Actions menu accessed within the RAYZ Curve Editor. For more information about each function, see the section on Controlling Interpolation of Curve Values in chapter 8.

Using Curves to Adjust Color Balance

The Color Curves node can also be used to adjust individual color channels. The procedure is the same as that described above for Making Tonal Adjustments, except that you work on the Red, Green, and/or Blue curves instead of the master curve.

Most commonly the Color Curves node is used to correct an imbalance in one color channel. For example, if an image has a bluish color cast, you can adjust the curve for the Blue channel.

You can also adjust color channel curves to simulate the color temperature of another sequence that was shot under different lighting conditions.

Color Curves Parameters

In addition to the curve graph, which is described in the previous section on Manipulating Color Curves, the Color Curves Node Panel includes the Curve Selector checkboxes and the Channel Select buttons.

Curve Selectors

The checkboxes at the top of the graph control which curve is visible in the graph. A curve must be visible to be edited. You can check any or all of the available curves, which include the master curve and the individual channel curves.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.

Note:

 

You can display and adjust the curve for any channel in the input image, even when it is deselected in this parameter. As long as the channel is deselected in Channel Select, however, the adjustment made to the curve will not be processed by the node until the channel is selected again.



Colorspace Node

 Colorspace node icon. The Colorspace node is used to convert imagery from one colorspace to another: RGB, HSV, YIQ, YUV, or CMYK.

The Colorspace node accepts one input, which may be any number of channels. The Alpha channel, if any, is also converted by the node.

Colorspace Parameters

Conversion

Use this menu to specify the type of conversion:



Contrast Node

 Contrast node icon. The Contrast node is used to vary the contrast of an image, or image channel, effectively compressing or expanding the tonal range. You also have the option of adjusting the point around which the distribution curve pivots to define the contrast value.

The Contrast node performs the following computation:

V = ((V - Pivot) * Contrast) + Pivot

The Contrast node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Note:

 

The Color Curves Node can be used to adjust image contrast when you need to manipulate the shape of the curve directly, as when you want to apply a nonlinear distribution function to the curve.

Contrast Parameters

Contrast

The Contrast parameter range is unconstrained, with the default value of 1.0 resulting in no change to the image.

Changing the contrast value changes the slope of the distribution curve that plots how the input values are remapped to the output. Higher values, which steepen the curve, increase contrast; lower values, which produce a shallower curve, decrease it.

Image showing graph of how the contrast parameter value controls the angle of the contrast curve.

Fig. 16.10 The Contrast value controls the angle of the distribution curve. Higher values create a steeper curve, which stretches the midtones while compressing the lows and highs.

If necessary, you can expand the parameter to access the channel controls, which work exactly like the master Contrast parameter but control each channel independently.

Pivot

The Pivot parameter controls the position of the axis about which the contrast curve will pivot. The Pivot value only affects the output image when the Contrast value is adjusted to a non-default value.

Image showing graph of how pivot parameter value controls axis of contrast curve.

Fig. 16.11 The Pivot value controls the axis of the Contrast curve, as illustrated here using a very steep Contrast curve.

A lower or higher pivot value has the effect of shifting the tonal distribution up or down to an extent determined by the Contrast parameter value (see Fig. 16.12).

Image showing graph of how pivot parameter value affects the output of the contrast node.

Fig. 16.12 Lowering the pivot shifts the midtones up, at the expense of the highest image values; raising the pivot shifts the midtones down, at the expense of the darkest image values.

The Pivot value is expressed in units based on the range of the input image colorspace: 0-255 for 8-bit; 0-65535 for 16-bit; 0-1 for floating point. By default the pivot point is centered in the colorspace, which would be a value of 0.5 in floating point.

If necessary, you can expand the Pivot parameter to access the channel controls, which work exactly like the master Pivot but control each channel independently.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



F-Stops Node

 F-Stops node icon. The F-Stops node simulates the process of using photographic stops to adjust exposure levels. When you need to adjust an image using f-stops as the unit of measure, perhaps because a DP has asked you to "bring it up a quarter stop," you can use this node without having to convert the requested adjustment into the equivalent parameter values used in other nodes.

The F-Stops node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

F-Stops Parameters

F-Stops

The F-Stops parameter has a range of 4 stops; that is, you can increase or decrease exposure by a maximum of 2 full stops. The range is -2 to 2, with the default value of 0 representing no change to the input image.

To decrease the image by a quarter stop, for example, enter -0.25 in the parameter field. To increase the image a half stop, enter 0.5.

If necessary, you can expand the parameter to access the individual channel parameters, which work exactly like the master F-Stops parameter but control each channel independently.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Gamma Node

 Gamma node icon. The Gamma node enables you to correct the gamma of an image. Gamma is an objective measure of the contrast in an image, equal to the slope of the characteristic curve. The characteristic curve, or gamma curve, is a plotted curve that illustrates the change in density of a negative as exposure increases.

The Gamma node performs the following computation (where V is the color value of a pixel):

V = V 1.0/Gamma

The Gamma node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Gamma Node Parameters

Gamma

Set the Gamma parameter by typing a value into the field or using the slider to set the value in a range of 0-3 (the actual range is unconstrained). The default value is 1, which represents no change to the input image.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Hue Adjust Node

 Hue Adjust node icon. The Hue Adjust node enables you to perform hue-based color adjustments to an image using the HSV (Hue, Saturation, Value) color model.

The Hue Adjust node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Hue Adjust Parameters

Image showing the Hue Adjust parameters in the Node Panel.

Fig. 16.13 Hue Adjust parameters in the Node Panel.

Hue

The Hue parameter is used to specify the hue shift for the input by rotating the color distribution vectors of the image 360° around the axis of the colorspace. The default value of the Hue parameter is 0, which represents no change from the input data.

You can perform the hue shift visually by dragging the color wheel (the inner circle of the wheel represents the input data), or you can enter a value representing the degree of color shift into the Hue field. For example, a value of 90 would shift pure red (0) to green (90) and green (90) to cyan (180).

Saturation

The Saturation parameter is used to adjust the chrominance level of the image in a range of 0 (complete desaturation) to 2. The default value is 1, which represents no change to the saturation of the input image.

Value

The Value parameter represents the relative intensity, or brightness, of the color data. The range is 0 (which would result in a black image) to 2 (blown out colors), with the default value of 1 representing no change to the input image.

Tip:

 

It is helpful to remember that two different hues with the same numerical brightness setting may not have the same perceived brightness. Also, the eye is more sensitive to changes in brightness at lower levels; for example, the difference in perceived brightness may be as great between numerical values of .10 and .11 as between .50 and .55.



Indexed Color Node

 Indexed Color node icon. The Indexed Color node is used to add a color wash, or tint, to a grayscale image. The color will be applied based on the distribution of luminance values in the input image to preserve the tonal gradations, textures, and shading of the original. You specify the color or colors to map to the luminance gradient, and those color values are interpolated linearly across the range.

The input image may be monochromatic or color. For a color input, however, the node will generate a monochromatic image by calculating the luminance values of the RGB image.

Tip:

 

The Indexed Color node is often used with the optional mask input, which will limit the colorization to a specific area when you want to change the color of a particular object in the scene, rather than the entire scene itself. For more information, see Using Mask Inputs in chapter 7.

Using Indexed Color

The Gradient parameter includes the gradient strip, which represents the tonal range of the image, and the color selection tools, which are used to assign specific color values to control points in the luminance gradient.

Image showing the use of the gradient color tools in the Indexed Color Node Panel.

Fig. 16.14 Gradient color tools in the Indexed Color Node Panel.

Gradient Control Points

Control points are indicated by triangle icons located along the bottom edge of the gradient. By default, the gradient has two control points, one located at the maximum luminance value (on the far right) and one at the minimum (on the far left).

You can add additional control points, and you can change the position of any control point along the gradient, that is, change the luminance value that a point controls:

The gradient must have a minimum of two control points to define the range. However, you can delete any additional control point you have created by selecting it (click on the triangle to be sure it is selected) and pressing the Delete key.

Assigning Color Values

To assign a color to a control point, you can drag a color from a swatch stored in the Image Viewer and drop it onto the control point. Alternatively, you can select a color from the spectrum strip located directly under the gradient and drag and drop it onto a control point.

In either case, when you release the mouse button over a triangle icon in the gradient, the color will be assigned to that control point and interpolated across the luminance range to the next control point.

You can also specify the color value for a control point numerically by selecting the point and using the color parameters underneath the spectrum strip. These color tools, which are common to a number of nodes in RAYZ, are described in detail in Using the Color Parameters in chapter 14.

Indexed Color Parameters

Index Channel

This menu specifies which channel to use in the node operation. By default, a luminance channel is selected, which has been generated from the RGB data. However, you can use an individual image channel instead by selecting it from the menu.

Luminance

This menu enables you to specify the type of luminance to be calculated when Luminance has been specified in the Index Channel menu. You can select Film, NTSC Video, or PAL Video. The formulas used by RAYZ to compute this data are in Appendix A: How RAYZ Computes Luminance Values.

Gradient

The Gradient parameter is used to apply color to the tonal range of the image as described in the previous section on Using Indexed Color.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Invert Node

Invert node icon. The Invert node automatically inverts the color values in an image, effectively creating a negative of the image. The Invert node performs the following computation, where Z is the maximum color value and V is the color value of the pixel being processed:

V = Z - V

The Invert node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Channel Select

Use the Channel Select parameter to specify which channels of the input image will be inverted. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Monochrome Node

 Monochrome node icon. The Monochrome node desaturates the color component of an image to the extent that you specify. The Monochrome node performs the following computation on each image channel in turn:

C = mN + C(1-m)

In this formula, C represents the channel value of the pixel being processed (the red, green, or blue component of the RGB triplet); N is the result of the Luminance computation; and m is the Amount parameter value.

The Monochrome node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Monochrome Parameters

Luminance

The Luminance parameter enables you to specify how the luminance value will be calculated. You can select Film, NTSC, or PAL luminance from the menu. For the formulas used by RAYZ to compute the three types of luminance, refer to Appendix A: How RAYZ Computes Luminance Values.

Amount

This parameter enables you to control the degree of desaturation of the image by entering a value in the range of 0 to 1, where 0 represents no change to the input image and 1 represents complete desaturation. The default value is 1, producing a fully monochrome image.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Printer Lights Node

 Printer Lights node icon. Printer lights are used by color timers in film labs to control the exposure, or density, of film prints. The Printer Lights node is designed to simulate the use of printer lights to control film density.

The Printer Lights node accepts one or two inputs. The second, optional input is used for a mask image. For more information, see Using Mask Inputs in chapter 7.

Using Printer Lights

The Printer Lights node might be used to compensate for color temperature or exposure problems in a filmed sequence or to match computer generated imagery to filmed imagery based on test prints of gray cards or other calibration material.

Parameter values in the Printer Lights node are in units that match the settings used to control printer lights in the lab, where each additional printer light increases log exposure by a specified fraction of a stop. The number of printer lights that is equivalent to a stop depends on the system used by the lab, typically 8 or 6 lights per stop. This value can also be adjusted in the node.

Any time that you need to make image adjustments in RAYZ based on reference data that has been specified in terms of printer lights, you can use this node without having to convert the values to work with the measurement units used in other nodes.

Printer Lights Parameters

The Lights parameter is used to adjust the image, and the Lights Per Stop parameter is used to adjust the unit scale of the Lights parameter to match the standard of the relevant color lab.

Lights

The Lights parameter is used to increase or decrease the number of printer lights. The master control affects the RGB channels equally, however you can expand the Lights parameter to adjust each channel individually.

The default value is 25, which is a standard printer setting for a normally exposed negative, and represents no change to the input image.

To increase exposure, increase the number of lights. Assuming that the Lights Per Stop parameter is set to 8, increasing the Lights parameter by 8 would double the exposure. Adding 16 lights to the default value would be equivalent to adding two stops, quadrupling the exposure of the input image.

Lights Per Stop

This parameter specifies how many printer lights must be added to double the film density value, that is, to add a stop. The default value is 8, which is used by Technicolor labs, but to match a Foto-Kem lab, for example, you would set this value to 6.

Channel Select

Use this parameter to specify which channels of the input image will be processed by the node. By default, the RGB channels of the input image are selected. To select or deselect a channel, press the button labeled with corresponding channel letter (such as A for Alpha) to toggle it to the opposite state.



Tint Node

 Tint node icon. The Tint node is used to adjust the color values of the input image to match the colorspace of another image. The Tint node remaps the color values based on high and low values you sample in the other image.

The Tint node accepts a single RGB or RGBA input.

Tint Parameters

Use the Tint parameters in the Node Panel to specify how the maximum and minimum values of the input image should be remapped (Map White To and Map Black To), and how much the image will change (Amount).

The "Map To" parameters use the standard RAYZ color controls, which are described in detail in Using the Color Parameters in chapter 14. Although you can expand the parameters to access numeric controls, the Tint node is designed to take values sampled from another image--the image you want to match--by using the eyedropper tool.

Tip:

 

You can pin the Image Viewer to the reference image to make it easier to sample. Alternatively, you can pin the Node Panel to the Tint node and select the reference image node in the Worksheet to display it in the Viewer.

Map White To

Click the eyedropper and sample a representative "white" area in the image you want to match. The whites in the Tint input image will be adjusted to match; that is, they will become bluer or warmer, brighter or darker, based on the new Map White To values.

Map Black To

Click the eyedropper and sample a representative "black" area in the image you want to match. The blacks in the Tint input image will be adjusted to match, based on the new Map Black To values.

Amount

Use the Amount parameter to decrease the effect of the "Map To" parameters, if desired, by decreasing the default value of 1 (full effect). The range is 0-1.



Video Safe Node

Video Safe node icon. The Video Safe node modifies the color information in an image if needed to conform to broadcast standards for NTSC and PAL video transmission. You choose which standard to conform to in the Video Type menu and the correction method to use in the Fix Method menu.

The Video Safe node accepts on input. Unlike most other color nodes, a mask input is not applicable to the operation performed by this node.

Because of the limited bandwidth of the broadcast video signal, certain high-intensity, highly saturated colors (pure red, for example) must be modified to reduce their amplitude to an acceptable level.

A given color is considered "unsafe" for transmission if the amplitude of its chrominance vector exceeds a predefined limit, or if the amplitude of the composite video signal exceeds a (different) predefined limit.

 

NTSC Video

PAL Video

Analog Colorspace Referenced

YIQ

YUV

Gamma Correction Value Applied

2.2

2.8

Max Chrominance Amplitude

50 IRE *

50 IRE

Max Composite Signal Amplitude

110 IRE *

110 IRE

* For NTSC video, the reference black level is offset by a pedestal of 7.5 IRE; therefore, the maximum composite signal amplitude is actually 102.5 IRE (110 - 7.5) and the maximum chrominance amplitude is actually 42.5 IRE (50 - 7.5).

The Video Safe node evaluates each pixel in the input image using standard conversion factors for RGB-to-YIQ (if NTSC video is specified) or RGB-to-YUV (if PAL video is specified).

If the color of a pixel exceeds the boundaries of the colorspace used by the selected standard, then that color is corrected by reducing either the intensity or saturation, as specified in the Fix Method menu.

Video Safe Parameters

Video Type

Use the Video Type menu to select the broadcast standard to which the output image should conform:

Fix Method

Use the Fix Method menu to select the method to use to modify any unsafe pixels in an image:

The best method to use will depend on the nature of the image being processed. As a general guideline, it is useful to remember that the luminance and chrominance values are encoded separately in broadcast video signals.

The chroma signal is derived by subtracting the luminance value of the color from the blue and red components: (B - Y) and (R - Y). The green component value is reconstructed from both luma and chroma signal information when the composite video signal is decoded by the receiving device.

This implies that the Reduce Saturation method, which reduces only the chrominance values--(R - Y) and (B - Y)--could increase the relative contribution of the green component to the output image and thereby alter the hue of the affected pixels.

The Reduce Intensity method, on the other hand, is more likely to darken the affected pixels.