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ColorYUV allows many different methods of changing the color and luminance of your images. ColorYUV is present in AviSynth from version 2.5 All settings for this filter are optional. All values are defaulting to "0" or false.
Parameters:
ColorYUV(clip [, float gain_y] [, float off_y] [, float gamma_y] [, float cont_y] [, float gain_u] [, float off_u]
[, float gamma_u] [, float cont_u] [, float gain_v] [, float off_v] [, float gamma_v] [, float cont_v] [, string levels]
[, string opt] [, boolean showyuv] [, boolean analyze] [, boolean autowhite] [, boolean autogain])
Description:
Gain, offset, gamma and contrast can be set independently on each channel.
Gain is a multiplier for the value. That means that if gain is set to 0, it preserves the values as they are. When gain is 256 all values are multiplied by 2 (twice as bright). If gain is 512 all values are multiplied by 3.
Offset adds a value to the luma or chroma values. An offset set to 16 will add 16 to the pixel values. An offset of -32 will subtract 32 from all pixel values.
Gamma adjusts gamma of the specified channel. A gamma value of 0 is the same as gamma 1.0. When gamma is set to 256 it is the same as gamma 2.0. Gamma is valid down to -256, where it is the same as gamma 0.0
Contrast adjusts contrast of the specified channel. Values are the mapped the same way as Gamma.
Levels can be set to either "TV->PC" or "PC->TV". This will perform a range conversion. Normally YUV values are not mapped from 0 to 255 (PC range), but a limited range(TV range). This performs conversion between the two formats. If no parameter is specified, no conversion will be made (default operation).
Opt can be either "coring" or "" (nothing, default setting). Specifying "coring" will clip your YUV values to the valid TV-ranges. Otherwise "invalid results" will be accepted.
ShowYUV can be true or false. This will overwrite your image with an image showing all chroma values along the two axes. This can be useful if you need to adjust the color of your image, but need to know how the colors are arranged. At the topleft of the image, the chroma values are '16'. At the right side of the image, U is at maximum. At the bottom of the screen V is at its maximum. In the middle both chroma is 128 (or grey).
Analyze can be true or false. This will print out color statistics on the screen. There are maximum and minimum values for all channels. There is an average for all channels. There is a "loose maximum" and "loose minimum". The "loose" values are made to filter out very bright or very dark noise creating an artificially low or high minimum / maximum.
Autowhite can be true or false. This setting will use the information from the analyzer, and attempt to center the color offsets. If you have recorded some material, where the colors are shifted toward one color, this filter may help. But be careful - it isn't very intelligent - if your material is a clear blue sky, autowhite will make it completely grey! If you add "off_u" or "off_v" parameters at the same time as autowhite, they will not be used!
Autogain can be true or false. This setting will use the information from the analyzer, and attempt to create as good contrast as possible. That means, it will scale up the luma (y) values to match the minimum and maximum values. This will make it act much as an "autogain" setting on cameras, amplifying dark scenes very much, while leaving scenes with good contrast alone. Some places this is also refered to as "autolevels".
Examples:
# This will adjust gamma for all channels (although less to y), while making 'y' larger:
ColorYUV(gamma_y=128, gamma_u=256, gamma_v=256, off_y=-16)
# Shows all colors. Frame 0 luma is 16, frame 1 luma is 17 and so on:
ColorYUV(showyuv=true)
# Recovers visibility on "very bad" recordings:
ColorYUV(autogain=true, autowhite=true)
