Bit Reduce NodeThe Bit Reduce node enables you to optimize the conversion of linear image data to a lower bit depth, to retain as much of the relevant data from the original image as possible. It also optimizes the conversion of Cineon 10-bit log image data to a linear format. The Bit Expand node is the complement to this node, performing the inverse of the Bit Reduce operations. Using Bit ReduceMost commonly Bit Reduce is used to convert Cineon 10-bit log or Cineon Linear files to 8-bit linear. ("Cineon Linear" refers to a Cineon file that has been converted to 16-bit or float linear using the default conversion in the Disk Input node.) The Bit Reduce node features two conversion methods specifically designed for this purpose: Cineon Softclip and Black & Rolloff. However, Bit Reduce also provides straight Linear conversion and the Curves method, in which you manually adjust the shape of distribution curves in a graph to control the conversion. These methods are suitable for converting 16-bit CGI to a lower bit depth. The Cineon Softclip, Black & Rolloff, and Linear methods all provide default values which can be adjusted to achieve the best result for a particular image. For predominantly light or dark images, you can use Light and Dark Intelligence to generate appropriate starting-point conversion values. The following steps provide a general guideline for using the Bit Reduce node:
Choosing a Conversion MethodThe Bit Reduce conversion method to choose will depend on your imagery and needs:
Black & Rolloff v. Cineon SoftclipThese methods are optimized for converting digitized film footage by providing the ability to apply a nonlinear curve to the highs to avoid harsh clamping. (Hence the terms "rolloff" and "softclip.") In Black & Rolloff , you specify the color values to use for the Low, Mid, and High values (for both the input data and the output). The conversion algorithm maps the values from Low to Mid in a linear curve and applies a nonlinear curve from the Mid to the High value to gradually roll off the highs. In Cineon Softclip , however, you do not map the low, mid, and high values from one colorspace to the other by assigning input and output values for each. Instead, you specify the low (Reference Black) and high (Reference White) values in the input data, and the conversion algorithm uses the Softclip value to compute a breakpoint above which the curve may become nonlinear. If the Softclip parameter is left at its default value (which is 0), the distribution curve remains linear along its entire length from low to high. In other words, this is a "hard" clip of input values above Reference White. As the softclip value increases, however, the slope of the curve from the breakpoint changes, gradually leveling off the curve for values above the breakpoint. The maximum recommended Softclip value is 100, which creates a curve from the breakpoint to the maximum color value of the input image. ![]() Linear v. CurvesThe Linear conversion method is a straight linear remapping of values. You specify the Low and High values to map from the input to the output. Curves , on the other hand, enables you to specify the distribution curve for each channel by manipulating splines in a graph editor. (For this reason, the Curves method uses a different configuration in the monitor panel.) Linear is the simplest method to use; Curves enables you to change the slope of the curve. Start by using Linear, and resort to Curves as your imagery requires. Conversion Parameter Tab![]() Work Monitor / At ResolutionFirst, select a display resolution for the work monitor from the At Resolution popup menu. Then click the plus icon to display the work monitor for this node, in which you adjust various conversion parameters. These parameters are described in the next section, "Bit Reduce Work Monitor ." Channel MaskThe Channel Mask parameter enables you to inhibit the modification of any channel by deselecting the Red, Green, Blue, Alpha, or Other channel buttons. Input IsThe Bit Reduce node accepts log or linear data. Use the "Input is" menu to inform Chalice which format type will be read for conversion. Output ToThe Output To menu is used to specify the data format to which the input imagery will be converted: 8-bit, 10-bit, 12-bit, 14-bit, or 16-bit linear. Frame Range IntelligenceFrame Range Intelligence allows you to draw the histogram information used by Light and Dark Intelligence from a range of frames rather than from a single frame. You can enter values directly from the keyboard or use the slider bar to set the range. The Light Intelligence and Dark Intelligence buttons work exactly like the ones located in the work monitor, which are described in the next section. Bit Reduce Work MonitorThe work monitor provides parameters to control the format conversion of the input and output types specified in the node panel. ![]() Light and Dark IntelligenceThe Light Intelligence and Dark Intelligence buttons can be used in conjunction with three conversion methods: Black & Rolloff, Cineon Softclip, and Linear. (The exception is Curves.) The default Low, Mid, and High conversion values used by these methods are optimized for "average" imagery. Because light images tend to contain more distinctions at higher color values than dark images, the optimal conversion values for predominantly light and dark imagery differ somewhat. Light Intelligence and Dark Intelligence instruct Chalice to set the conversion parameters accordingly. To use Light or Dark Intelligence:
The Low and High parameters for all three conversion methods are set to the minimum and maximum values in the input image that occur above a certain frequency. These values remain the same for both Light and Dark Intelligence. (This means that you will achieve the same result by using either option when Linear is the selected conversion method, because the Linear method does not use a mid value.) If you are using Black & Rolloff or Cineon Softclip, Intelligence will also generate a midrange value. This value is entered as the Reference White parameter value for Cineon Softclip and the In Mid value for Black & Rolloff. Dark and Light Intelligence use different algorithms to generate this value:
![]() Parameter MenuThis menu allows you to select the conversion parameters to display for the type of conversion you specified in the Conversion menu. For example, if Black & Rolloff conversion is specified, this menu will allow you to view and change the In Low/Out Low, the In Mid/Out Mid, and the In High/Out High parameters in the tuners below the menu. The fourth conversion method, Curves, displays a different interface (to manually adjust curve shapes) in the monitor panel. Conversion ParametersThese two columns of tuners enable you to change the default mapping values used by the selected conversion method: Black & Rolloff, Cineon Softclip, or Linear. For Black & Rolloff and Linear, the left column represents input image values to map to the output image values in the right column. (Cineon Softclip is an exception.) The following "method" descriptions give guidelines for using these parameters. The Conversion parameters display a pair of values for the currently selected Parameter menu item. Separate tuners are provided for each channel to allow you to change them individually. Values can be animated by double-clicking the STED button associated with each column to access the STED window. For more information, see chapter 9, "Space-Time Editor (STED) ."
Use the "Display Unit" buttons to change how parameter values are displayed, to work with the numbers that are most applicable to the situation. For example, you can view the default Reference Black/Reference White parameter values used by Cineon Softclip either as Cineon (95 and 685 respectively) or as linear (44 and 4095). Conversion MenuThis menu allows you to select the method Chalice will use to convert the input format to the output format. The default is Black & Rolloff. You can also use Cineon Softclip, Linear, or Curves. Each conversion method is described below. Black & Rolloff MethodBlack & Rolloff is used to convert Cineon-type files. The Black & Rolloff method enables you to specify Low, Middle, and High color values for the input (In column) and the output (Out column) colorspaces. The values from the Low to Mid point value are converted linearly, while the values from the Mid to High point are gradually "rolled off" in a nonlinear curve. ![]() One advantage of the Black & Rolloff method is that you can inspect the input image to determine the actual image values on which to base conversion values. The default values are based on Cineon specifications, and take into account some of the characteristics of negative film. For example, negative film is not perfectly clear; consequently, the lowest pixel values in the range are not used. So rather than map 0 in the input to 0 in the output, 44 in the input is mapped to 0 in the output. The more unused pixels you can exclude from the conversion, the more room there will be to map meaningful pixels into the smaller bit space. Bit Reduce lets you specify the best Low, Mid, and High values for the particular image you are converting. Do you need more space for distinctions among lower values? Set the Mid value higher. Does the image have specular highlights you don't want to lose? Increase the High value and/or lower the Mid value. The Low parameters specify the optimal black point. The default for the In Low is 44, the equivalent of 95 in 10-bit log space, which is mapped to 0 in the Out Low. The Mid values set the top end of the midrange mapping points for the conversion. The default In Mid value is 4095, the equivalent of 685 in log space, which represents the 90% density point in the source image. By default it is mapped to 245 (8-bit) or 62965 (16-bit) for the Out Mid value. Values above this point will be gradually rolled off to the specified High value. The High value represents the point at which the input will be clamped to maximum in the output. The default In High value is 20,000 (or 892 in log space). You may want to use the Inspect panel or other display tool to determine the best In High value to map to the Out High value, which is the maximum value in the output colorspace (i.e., 255 in 8-bit). Cineon Softclip MethodLike Black & Rolloff, the Cineon Softclip method is used to convert Cineon 10-bit log and Cineon Linear image data to another colorspace, such as 8-bit linear. This method provides a Softclip parameter that can be used to control the slope of the conversion curve at the high end to eliminate the effects of harsh clamping. The Softclip conversion assigns output values by taking the inverse log of the input Cineon data, then scaling and adjusting according to the Reference White, Reference Black, Film Gamma, Display Gamma, and Softclip parameter values, and the output format. (Refer to the equations in appendix C, "Softclip Conversion ," for the precise conversion process used in the Softclip operation.) The default parameter values for Cineon conversion are based on specifications published by Cinesite (1993) and Kodak (1995). Both of these documents are available for downloading from the Silicon Grail website (www.sgrail.com). Reference Black specifies the lowest value included in the conversion. All pixels with color values below this number will be set to zero in the output image. The default value is 44 (95 in log). The Reference White parameter represents the 90% white value. The default value is 4095 (685 in log). Film Gamma refers to the gamma, or color distribution curve, of the input image. Display Gamma refers to the gamma of the workstation monitor on which the output image will be displayed. The defaults are 0.6 and 1.0, respectively. Softclip allows you to gradually level off the distribution curve for colors above Reference White. The Softclip value is subtracted from Reference White to create a breakpoint. The slope of the curve changes above the breakpoint, rolling off the highs. Softclip should be considered a log value; that is, it is subtracted from the log value (i.e., 685) of Reference White, not the linear (4095). The default Softclip value is 0, which will create a linear curve from Reference Black to Reference White, clamping all values above Reference White. A Softclip value of 100 creates a nonlinear curve, starting from the breakpoint, that gradually levels off to the maximum color value for the input image. ![]() Linear MethodThe Linear method is the most direct way to convert non-Cineon 16-bit linear imagery to a lower bit depth. As the name implies, it is a straight linear conversion that maps the specified low and high value in the input image to the specified low and high for the output. Chalice will assign all values in between in a linear fashion. In the In Low/Out Low parameters, the left column represents the lowest input value to map to the low value specified in the right column (representing the output). All values below the In Low value will be clipped to the Out Low value. In the In High/Out High parameters, the left column represents the highest input value to map to the corresponding value in the right column (the output). All values above the In High value will be clipped to the Out High value. Curves MethodThe Curves method allows you to manually adjust the format conversion curves in the graph. Unlike the other conversion options, you do not specify a value for predefined parameters, which are then used by a conversion algorithm to generate a distribution curve for the conversion. Instead, you alter the curves for each individual channel by manipulating splines on a graph using points and slope functions. Selecting Curves from the Conversion menu changes the configuration of the Bit Reduce work monitor panel. The Curves Editor panel is displayed, which provides the tools needed to manipulate the conversion curves for each channel. The Bit Reduce Curves Editor section describes in detail how to use these tools. Display Unit ButtonsThese four buttons allow you to change the numerical units used to display values in the Bit Reduce work monitor. These settings affect the display of Conversion parameter values, Conversion Graph values, and Color Picker values. (The Color Picker display is controlled by the top row of buttons only.) The two sets of buttons work together as follows: Top Row (Integer/Float):
Bottom Row (Linear/Log):
Conversion GraphThe graph visually illustrates the specified conversion scheme. The horizontal axis represents the input image. For example, if the input is 16-bit linear, the horizontal axis will be in the range of 0-65535. The vertical axis represents the output. For example, if 8-bit is the selected output, the vertical axis will range from 0-255. Graph Display ButtonsThese buttons can be used to change the data format in which the input image is displayed from the default. The default view (the "D" button) displays the horizontal axis in the same range as the input.
The graph also displays a histogram of the color distribution of each input channel. You can zoom in on sections of this histogram by sliding the triangular wedges located on the right of the graph. Channel Display ButtonsThese buttons turn on and off the histogram display for each input channel. All channels are turned on by default. Bit Reduce Color PickerThe Color Picker features two color boxes, each of which can display the RGBA value of any pixel or pixel area in an image. The Color Picker is especially useful for comparing color values in two different images using A/B Wipe. ![]() To use the Color Picker, simply click the mouse in one of the two Color Meter boxes . The cursor will change into an eye dropper--this is the Color Picker tool. Then click on any pixel in the image that you want to meter. The color values of that pixel will appear in the Color Meter box and the cursor will revert to normal shape. If you are sampling an area of pixels, their average will be displayed. To sample an area of pixels, click the Sample Size Selector to select the appropriate size pixel grid from the popup menu: 1x1, 3x3, 5x5, 7x7, 9x9, or 11x11. Color Picker values can be displayed as integer or float. Click the "D" button to display integer values (in the selected output depth). Click "F" to view the values in float. Bit Reduce Curves EditorThe Curves Editor panel appears when Curves is selected from the Conversion menu: ![]() In the Curves Editor panel, you can manually adjust the conversion curves in the graph. The Channel Display buttons determine which curves are displayed and activated for editing. The Slopes menu enables you to apply various function curves. You can add a new value point anywhere on a curve by clicking on that part of the curve. To delete a point, click on the point to select it and then press the Delete key on the keyboard. To move a value point, click on it and drag it to a new location.
Channel Display ButtonsThese buttons allow you to display or suppress the color curve for a given channel. Only curves that are displayed can be altered. Keyframe Editor ButtonsThese buttons allow you to set key frames to vary the curves over time. Click the button once to activate the channel for animation. Then you can use the Key Framer on the node panel to set key frames, or click the Keyframe Editor button again to bring up the Keyframe Editor window for the associated channel. In the Keyframe Editor, select a key frame by clicking it once (it will highlight). You can move the key frame by dragging it. You can copy or delete any selected key frame by right-clicking in the editor window to display a popup menu with these two choices. When you select "Copy," the currently selected key frame is copied to frame number under the cursor. Slopes MenuThe Slopes menu allows you to specify the type of curve that goes into and out of each value point. The following choices are available:
Value Point ParametersThe Input, Output, Slope In, and Slope Out tuners display values for the currently selected point on a curve in the graph. As an alternative to dragging a point or handle to reposition it, you can key specific values into the data entry fields to remap values. The Input parameter displays the color value of the selected point for the image being converted, while the Output parameter displays the corresponding value for the converted output image. The Slope In and Slope Out parameters display the slope into and out of a specified value point. The minimum and maximum values are 0 and 10, respectively. If the Equal Slopes or Different Slopes function has been selected from the Slopes menu, the fields become active and you can key values into the data fields to define the slopes. Curves Editor ButtonThis button brings up a larger graph than the one provided in the workspace. It provides a resizable window that can make selecting and moving curves easier. Otherwise, it has the same functionality as the graph in the Curves Editor panel. Advanced - Cineon Settings Parameter TabThe parameters in this tab represent default values that are used internally by the Bit Reduce node as part of the Cineon Softclip algorithm. They do not represent values sent directly to output. In most cases, these parameters should be left at their default values, which are based on specifications published by Cinesite and Kodak. They are provided for those specialists in film digitization who may wish to change the defaults for certain sequences. Refer to appendix C, "Softclip Conversion ," for more information. |