'Lab' is an acronym that spells Lightness, channel A, and channel B. In 'Lab mode', greyscale channels are translated into the following instead of the more common RGB mode.
- Lightness (luminance): or simply known as brightness channel.
- Channel A: consist of colors from red to green, and
- Channel B: consist of colors from blue to yellow
Conversion to Lab mode is useful for preserving the original color value while enabling change to certain aspects of the image. In terms of sharpening an image, lesser artifacts and noise would be produced, whilst ensuring color data are unaffected. This ultimately contributes to better quality prints during post production.
Example:
Image below may already contain subtle artifacts and noise. We want to sharpen objects in an image without increasing the effect or visibility of those unwanted elements and also in a way that does not affect the original colors.
A brief note on Unsharp Mask before advancing:
Unsharp Mask is a filter that sharpens objects in an image, or in other words increase edge contrasts to objects in an image.