My question is based on this link.

https://docs.opencv.org/4.6.0/db/da5/tutorial_how_to_scan_images.html

The tutorial introduces colour space reduction. But I don't understand its equation. I believe that if you want to do colour reduction you can simply do (i/divideWith) without multiplying divideWith.

CodePudding user response：

The expression is table[i] = (uchar)(divideWith * (i/divideWith))

The whole point of that is to exploit integer division (innermost parenthesis, i/divideWith) to cause discretized colors.

Mathematically, this (over-)"simplifies" to table[i] = i, which means the range is approximately maintained.

If you didn't multiply "back" after dividing, you'd get smaller values, rather than values stretching mostly the whole 0 .. 255 range, and that would make your picture very much darker. In fact, the integer division is rounding down, so that already makes your picture darker.