RGBAdjust

RGBAdjust (clip, float "r", float "g", float "b", float "a", float "rb", float "gb", float "bb", float "ab", float "rg", float "gg", float "bg", float "ag", bool "analyze", bool "dither")

This filter multiplies each color channel with the given value, adds the given bias offset then adjusts the relevant gamma, clipping the result at 0 and 255. Note that RGBAdjust (1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1) leaves the clip untouched.

r (-255.0 - 255.0; default 1.0): This option determines how much red is to be scaled. For example, a scale of 3.0 multiplies the red channel of each pixel by 3. Green and blue work similar. a (-255.0 - 255.0; default 1.0) specifies the scale of the alpha channel. The alpha channel represents the transparency information on a per-pixel basis. An alpha value of zero represents full transparency, and a value of 255 represents a fully opaque pixel.

In v2.56 the bias offsets rb, gb, bb, ab (default 0.0) add a value to the red, green, blue or alpha channels. For example, rb = 16 will add 16 to the red pixel values and -32 will subtract 32 from all red pixel values.

Also in v2.56 the exponents rg, gg, bg, ag(default 1.0) adjust the gamma of the red, green, blue or alpha channels. For example, rg = 1.2 will brighten the red pixel values and gg = 0.8 will darken the green pixel values.

In v2.56 analyze (can be true or false) will print out color statistics on the screen. There are maximum and minimum values for all channels. There is an average and a standard deviation for all channels. There is a "loose minimum" and "loose maximum". The "loose" values are made to filter out very bright or very dark noise specs creating an artificially low or high minimum / maximum (it just means that the amount of red/green/blue of 255/256 of all pixels is above (under) the loose minimum (maximum)).

dither = true/false (false by default): When set to true, ordered dithering is applied when doing the adjustment.

Keep in mind ALL the values are not scaled to accomodate changes to one (for that you should use levels) so doing something like:

RGBAdjust(2, 1, 1, 1)

will get you a whole lot of clipped red. If you WANT a whole lot of clipped red, there you go - but if you want MORE red without clipping you should do

Levels(0, 1, 255, 0, 128).RGBAdjust(2, 1, 1, 1)

This would scale all the levels (and average lum) by half, then double the red. Or more compact

RGBAdjust(1.0, 0.5, 0.5, 1.0)

This leaves the red and halves the green and blue.

To invert the alpha channel

RGBAdjust(a=-1.0, ab=255)

Thus alpha pixels values become a=(255-a)

Changelog:
v2.56	Added offsets, gamma, analyze.
v2.60	Added dither.

$Date: 2011/12/04 15:28:44 $