Image adjustments

The following options alter the image itself in various ways. This processing is performed on the cached RAW-converted image.

option+value

option–value

The value is always a percentage figure, more or less, that adjusts the given parameter away from the default.

Options

red

green

blue

Increase (+) or decrease (-) the level of the given channel. This uses a gamma curve on each channel to avoid clipping. Values can be no less than -100, while there is no limit on the positive value. A value of +10 will give a slight increase in the channel, +100 will gave a very large increase. These options are also useful when doing black and white conversion to adjust the amount of each channel that is used for the conversion.

black

white

Increase (+) or decrease (-) the amount of black or white in the image. In the case of the + values, the histogram is stretched by the given amount, resulting in more “black” or “white” in the image, and possible clipping. IN the case of – values the histogram is compressed, resulting in a reduction in contrast.

gamma

Apply a gamma curve to the image. Values can be no less than -100, while there is no limit on the positive value. A value of +10 will give a slight increase in mid-tone brightness, while +100 will gave a large increase.

contrast

mid

Apply a sigmoidal contrast curve to the image. The contrast parameter sets the amount, with +10 being small, and +100 being quite a lot. Negative values will decrease image contrast. The mid parameter adjust the mid-point of the contrast curve away from the default 50%, in percentage point; it must therefore range between -50 and +50.

brightness

saturation

hue

Adjust the image’s brightness, saturation, and hue, using the HSV colorspace.

-+-

Clear the image adjustment options.

The image adjustment parameters can be provided as arguments to the following commands: generate, options and variant.

Examples

Reduce the colour temperature slightly:

red+5 blue-5

Brighten midtones an underexposed image without clipping highlights, and add lost contrast and color:

gamma+40 mid-20 contrast+50 saturation+15

Reduce image contrast for use as a page background:

black-30 white-30