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      Effect:RGBA Replace
      Category:Spatial Filters
      Speed:Fast

      Description: The RGBA Replace Effect is extremely important in Pena as it lets you replace a particular range of color while painting. This is a simpler, and faster to setup, version of the Selective Replace Effect.

      Replace Effects let you set a range of color. If Color 1 matches that range, it is replaced with Color 2 (or vise versa, depending on the options).

      Note that all four channels, including Alpha, are replaced. This allows you to replace a solid color with a transparent color (effectively a Discard though future Effects will still be applied, unlike Discard).

      RGBA Replace takes a single Minimum value and a single Maximum value. When the Minimum is smaller than the Maximum, any colors that fall between (and including) the Minimum and Maximum are replaced.

      If the Minimum Value is higher than the Maximum, then this acts as a Notch Filter. Colors below the Maximum and colors above the Minimum are replaced.

      To help illustrate this consider the following:

      In the above image, black represents the value 0 and white is 255. In the top illustration you can see that when the Minimum is lower than the Maximum, the colors in between those two values are replaced. However, in the bottom illustration Maximum is below Minimum. You can see that the opposite colors, from the first illustration, are replaced.

      You will also notice that there are no Output Color options for RGBA Replace. This is because you set this Effect to work on Color 1, or Color 2. It outputs the Color you select to use (in the Options).

       
      Options: The RGBA Replace Effect has the following Options Pane:

      Change Color 2:If set to a Red X then Color 1 is used for the range check and matching ranges are replaced with Color 2. If set to a Green Check Mark then Color 2 is used for the range check and matching ranges are replaced with Color 1.
      RGBA Minimum:This value works together with RGBA Maximum to determine what range of colors to replace. When this is lower than RGBA Maximum, any colors between, and including, RGBA Minimum and RGBA Maximum will be replaced with the alternate Color. When RGBA Minimum is larger than RGBA Maximum, the test is inverted. Colors between the Maximum and Minimum are left unchanged, and colors outside that range are replaced with the alternate Color.
      RGBA Maximum:This value works together with RGBA Minimum to determine what range of colors to replace. When this is lower than RGBA Maximum, any colors between, and including, RGBA Minimum and RGBA Maximum will be replaced with the alternate Color. When RGBA Minimum is larger than RGBA Maximum, the test is inverted. Colors between the Maximum and Minimum are left unchanged, and colors outside that range are replaced with the alternate Color.
      Compare Red:If set to a Red X then the Red Channel will not be included in the range check. If set to a Green Check Mark then the Red Channel is considered in the range check.
      Compare Green:If set to a Red X then the Green Channel will not be included in the range check. If set to a Green Check Mark then the Green Channel is considered in the range check.
      Compare Blue:If set to a Red X then the Blue Channel will not be included in the range check. If set to a Green Check Mark then the Blue Channel is considered in the range check.
      Compare Alpha:If set to a Red X then the Alpha Channel will not be included in the range check. If set to a Green Check Mark then the Alpha Channel is considered in the range check.
      Invert Decision:If set to a Red X then the decisions to replace are as described above. If set to a Green Check Mark then the decision to replace is reversed. That is, if the above settings would have resulted in a replace, it is not replaced, and vice-versa.

      Example: To show some uses of RGB Replace we start by combining an image with two Effects.

      In Slot 1 we have a 2-Color Gradient with default values. In Slot 2 we have our Arches National Park photo loaded via a Texture Effect:

      In Slot 3 we place our RGBA Replace with default values. The result is this image:

      Since the default Minimum is 0 and the default Maximum is 64 this means that any Color 1 RGB values between 0 and 64 will be replaced with Color 2 (the texture). Since the 2-Color Gradient Effect produces black (0) at the bottom, and white (255) at the top, you can see the precise area that was replaced with the texture - only the values between 0 and 64.

       

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