Channel Remap (HSV)

Usage

For each of the output channels, you can select one input channel to use for that output channel.

By default, each channel is mapped to itself: hue to hue, value to value, saturation to saturation, and alpha to alpha.

For each channel, you can select from the following options:

• H - Uses the value of the hue input channel.
• S - Uses the value of the saturation input channel.
• V - Uses the value of the value (brightness) input channel.
• A - Uses the value of the alpha (opacity) input channel.
• Y - Uses the weighted luminance of the layer (see Weighted Y, below).
• 0 - Uses the minimum value for this channel (see Minimum and Maximum values, below)
• 1 - Uses the maximum value for this channel (see Minimum and Maximum values, below)

Channels

Technically speaking, layers do not have hue, saturation, or value channels. This effect converts the RGB channels to HSV, remaps them, and then converts them back to RGB channels for output.

Minimum and Maximum Values

For the Hue channel, the minimum (0) and maximum (1) values are both red, as hue represents progression around the color wheel starting from red.

For the Saturation channel, the minimum value (0) represents a completely desaturation color (black, gray, or white) and the maximum value (1) represents a fully saturated color.

For the Value channel, the minimum value (0) is black, regardless of the value of the other channels, and the maximum value (1) is the brightest representable color of the selected hue and saturation (white if saturation is 0).

For the ALpha channel, the minimum value (0) is transparent, and the maximum value (1) is opaque. But see Alpha Handling, below, for some caveats.

Weighted Y

This effect has two similar but distinct channel inputs: V (value or brightness) and Y (luminance). The value or brightness is calculated based on the original red, green, and blue intensities. For example, if a color such as pure red were hue-rotated to green witout changing the value or brightness, the result with be to effectively swap the red and green channels.

This is not always desirable because to humans, green light appears brighter than an equivalent intensity of red light.

The luminance value provides an alternative option than compensates for this. Luminance is weighted so that it appears natural to humans.

For example, given the same value for the green and blue channels, the green channel is considered to have higher luminance because a given intensity of green light appears brighter to the human eye than the same intensity of blue light.

The exact formula used is:

Y = R * 0.2126 + G * 0.7152 + B * 0.0722

Alpha Handling

Setting the alpha channel to 1 on a layer with transparency can have unpredictable results in some cases: Even though a pixel is completely transparent, the RGB data for that pixel may still exist (albeit, not visibly becuase the alpha is zero). Therefore, forcing the alpha to 1 can result in the display of "garbage" data from completely transparent pixels.

In addition, depending on the phone or tablet you are using, pixels with an alpha of zero might have had their RGB cleared to black or premultipled by the alpha value (this reducing the color resolution of the data).

Forcing Alpha to 1 is best used only if the inputs of the other channels are not R, G or B.

Use Cases

• Make an alpha mask out of saturation or value channels. Set S to 0, V to 1, and A to either S, or V. To adjust the color, combine with another effect afterwards.

• Make a rainbow from the layer’s saturation, brightness, or luminance. Set V to 1, S to 1, and H to S, V, or Y.

• Make a luminance (grayscale) map from the layer’s hue or saturation. Set S to 0 and V to H or S. You can then use this for effects that take a luminance map, such as displacement map, hot color, etc.