Transform Node

The Transform node enables you to rotate, translate, or scale an image, or insert a smaller image into a larger image.

You can use the Transform node to animate the motion of one image relative to another or to control the specific placement of composited imagery. You can also simulate camera moves such as pans or zooms, or wildly complex shots that integrate pans, zooms, translations, or rotations.

The Transform node accepts one or two inputs:

  • The top input is the image to be transformed.
  • The optional bottom input defines the dimensions of the output and serves as a visual reference in the Transform work monitor.

Transform Parameter Tab

The Transform tab provides two groups of parameters: the first group controls the work monitor display; the second group governs the actual transformations.

Work Monitor Display Parameters

The first set of parameters in the Transform tab control work monitor display:

Work Monitor / At Resolution

First, 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.

Note:
Assuming that you have used the optional bottom input to the Transform node, the work monitor will display both input images in a temporary composite, with the input to be transformed (the top input) over the background image (the bottom input). This enables you to use the second input image as a reference while you operate on the primary image.
However, only the primary image will be output from the node. To actually composite the imagery, you would use a composite node such as Mcomp.

The Transform work monitor enables you to interactively control the Rotate, Scale, and Translate parameters using a boundary box and circle-with-crosshairs device that includes four radial control lines around the outside of the circle.

Hot Keys:
You can use the arrow keys on your keyboard to Translate, Scale, and Rotate in small increments. Each nudge will update both the work monitor display and the associated parameter fields.
The default mode for the arrow keys is Translate. To scale or rotate, you hold down a modifier key while pressing the arrow keys: to scale, hold down the "s" key; to rotate, hold down the "r" key.

Translate is a 1-pixel nudge. Rotate is a 1-degree nudge. The scale nudge is a fraction of image size: 10 / max(xres,yres)

Transparency

This parameter is used to set the level of transparency of the top input over the (optional) bottom input as it is viewed in the temporary composite displayed in the Transform work monitor.

Use Image Alpha with Transparency

When this option is checked, the alpha channel value of each pixel of the primary input is multiplied by the Transparency parameter value to govern the overall transparency of the temporary composite image in the work monitor.

Input Is Premultiplied

Check this box to inform Chalice when the primary input to the Transform node is a premultiplied image. For more information About Premultiplication , refer to chapter 15.

Transformation Parameters

The Rotate, Scale, Translate, and Pivot parameter fields update to reflect any modifications you make using the interactive crosshairs device in the work monitor. You can also set these parameters by entering values directly into the parameter fields and you can use hot keys to transform, scale, or rotate in small increments (refer to the diagram in the previous section).

Order

This menu enables you to specify the order in which the transformation operations will be computed. The default order--scale first, then rotate, then translate--is likely to be the best choice in most cases, where the pivot point will be at the center of the image being transformed. But for transformations where the pivot will be located at a corner (a swinging arm motion, for example), then the "Translate, Rotate, Scale" option would be preferable.

Rotate

The Rotate parameter enables you to rotate the top input image. Values are expressed in degrees (0-360). A positive value rotates the image in a counterclockwise direction. Alternatively, you may enter a negative value to rotate the image in a clockwise direction. The rotation is centered around a pivot point that you specify by using the Pivot parameter.

Scale

The Scale parameter enables you to scale, or proportionally adjust the total size of, the top input image. The scale is centered on a pivot point that you specify in the Pivot parameter.

The Scale parameters are simple multiplier values for the X and Y coordinates. The 0,0 point is the lower-left corner of the source image. For example, full size (no change to the input) is expressed by values of 1,1 in the data entry fields. And entering 0.5 in both fields will create an image that is half as high and half as wide as the source image.

Translate

The Translate parameter enables you to shift the position of the top input image along the X and Y axes.

You set the Translate parameter by keying in a pair of numerical values. The first value shifts the image along the X axis (horizontally). The second value shifts the image along the Y axis (vertically). The distance is measured as a percentage of the X or Y axis within a range of 0 to 1. For example, values of 0.5, 0.0 will shift the image to the right a distance equal to one-half the width of the image.

Pivot

The Pivot parameter enables you to specify a pivot point to be used in conjunction with the Rotate and Scale parameters (see above). The pivot point is the center of the rotation or scale.

You set the Pivot parameter by keying in a pair of values in the range of 0 to 1. These values represent an x,y location specified as a percentage of the image width and height. The lower-left corner of the image is the 0,0 point; the upper-right corner of the image is located at 1,1; the center of the image is 0.5, 0.5.

Filtering

This menu enables you to select an option for filtering the transformation operations. The default is "Best (Dynamically Chosen," however, you can select "Good ( Bilinear Interpolation)" to speed processing, or the fastest option, "Fast (No Filtering)," when image quality is not a top concern, as when reviewing your initial transformation settings. The fourth option, "Advanced - User Set," enables the parameters on the Filtering tab, which provide control over the type of filtering to use for the current imagery and operation.

Motion Blur

Check this box to enable motion blur for the transformation. To control various aspects of the motion blur, you can then adjust the parameters on the Motion Blur tab.

Filtering Parameter Tab

The parameters in the Filtering tab are enabled when the "Advanced - User Set" option is selected from the Filtering menu on the Transform tab.

Filter Type

The Filter Type menu includes Box, Triangle, Quadratic, Cubic, and Gaussian; as well as Catmull-Rom/Overhauser Spline, Mitchell, Sinc (Windowed), Bessel (Windowed), Lanczos 2-lobe Sinc, and Lanczos 3-lobe Sinc.

Box, Triangle, Quadratic, Cubic and Gaussian refer to the shape of the function curve that defines the filter. Box equals constant, triangle is linear; and so on in increasing precision and processing time.

The other filter options are named for the individuals who developed them, and the best choice will depend on the individual characteristics of the image as well as on the type of operations the node is performing.

The Mitchell and Lanczos filters are among the most popular filter options. Mitchell filtering is often preferred for Jpegs or images with a lot of fine lines. Lanczos filtering provides a good compromise between sharpness, ringing and aliasing reduction. It is best used on images which are reduced or scaled down.

Mitchell B and C

The Mitchell B and C parameters are activated when Mitchell filtering is selected in the Filter Type menu to enable you to make adjustments to the Mitchell filtering process. The default values, 0.333 for both parameters, fall within a recommended range of roughly 0.25 to 0.5. Since the quality of the result must be judged based on your imagery and intentions, the best course may be to experiment with these settings.

As a guideline, values above 0.5 for Mitchell B may produce unnecessary blurring. Values above 0.5 for Mitchell C may result in excessive ringing (rippling patterns). When both parameters are set at values above 0.6 or below 0.2, anisotropic artifacts may appear.

Window Type

The Window Type parameter is activated only when the Sinc or Bessel filter type is selected from the Filter Type menu. Choices are Hanning, Hamming, Blackman, or Kaiser.

Kaiser A

When Kaiser is chosen in the Window Type parameter, this parameter is activated.

Blur

The Blur parameter can be used with any filter option when heavy blurring is needed. The default value of 1 adds no blurring to the image; values greater than 1 represent increased blurring, up to the maximum of 4.

Motion Blur Parameter Tab

These parameters are activated Motion Blur is enabled on the Transform tab.

Shutter Phase

The Shutter Phase parameter enables you to specify where in a frame to "open the shutter," in a range of -1 to 1. The default is 0, which represents the center of the frame.

Shutter Speed

The Shutter Speed parameter enables you to specify the duration of the effect for each frame in a range of 0 to 2, where 2 represents the duration of one complete frame.

Automatic Sampling

Automatic Sampling is enabled by default, to let Chalice set this value for the operation. However, you can turn off this feature to set a specific value in the Samples parameter.

Samples

The Samples parameter enables you to specify the number of subframes to examine when computing the motion, when you have disabled Automatic Sampling. The faster the motion in the sequence being blurred, the greater the number of samples needed. Larger values mean longer processing times.




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