Photo editing

Image editors have provisions to simultaneously change the contrast of images and brighten or darken the image. Underexposed images can often be improved by using this feature. Recent advances have allowed more intelligent exposure correction whereby only pixels below a particular luminosity threshold are brightened, thereby brightening underexposed shadows without affecting the rest of the image. The exact transformation that is applied to each color channel can vary from editor to editor. GIMP applies the following formula:[4] if (brightness < 0.0) value = value * ( 1.0 + brightness); else value = value + ((1 - value) * brightness); value = (value - 0.5) * (tan ((contrast + 1) * PI/4) ) + 0.5;