The commands in this menu are meant for adjusting the image in various ways to get the colors to look the way you want.
This image will be used to illustrate what the various adjustments can do:
This can be used to equalize the colors of an image so that overly dark or bright images are brought back to a normal range. This is equivalent to using the Levels adjustment and then clicking the "Auto" button.
After using the Auto-Level adjustment, which has no configuration options
This may be used to make the colors in an image brighter or darker, or to make colors stand out more or less from those around them.
Image with increased brightness
Image with increased contrast
Image with increased brightness and contrast
This adjustment is used to adjust the luminosity and/or RGB (Red, Green & Blue) curves of an image. For greater discussion of this functionality, please visit the Curves section.
This adjustment removes all color, effectively making the layer black & white.
Image that has been desaturated
This operation may be used to change the saturation of colors, as well as rotate the hue of the image. Additionally, it allows the adjustment of lightness, which is similar to but not the same as brightness.
Image after the Hue was set to 88 and the Saturation was set to 158
This adjustment is very similar to a negative of a photo. Applying it a second time produces the image again.
Image after it has been inverted
This operation is used to adjust the color range and gamma of an image. For greater discussion of this functionality, please visit the Levels section.
This adjustment allows you to reduce the number of available color values that each pixel may use. Normally each color channel has 256 possible values (0 through 255), but with this you can restrict this to a range from 2 to 64 values. This gives your image a "posterized" or even a retro or "faux dithered" look.
Image after the "Posterize" Adjustment
This adjustment turns the image black & white, and then adds a sepia tone. This can be used to give your images an "aged" look.
Image after the "Sepia" Adjustment