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isp:brightness [2022/04/04 23:32] – external edit 127.0.0.1isp:brightness [2023/09/05 04:36] – Igor Yefmov
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 Again, in the simplest terms, increasing or reducing pixel's brightness can be interpreted as adding or subtracting a fixed "gain" value (others may argue that a more natural approach would be to use a multiplier, while others still may bring the "vibrancy" approach into picture). Again, in the simplest terms, increasing or reducing pixel's brightness can be interpreted as adding or subtracting a fixed "gain" value (others may argue that a more natural approach would be to use a multiplier, while others still may bring the "vibrancy" approach into picture).
 +
 +===== In RGB color space =====
 +In RGB color space the operation is a matrix multiplication of the RGB's vector by a given "brightness" matrix. However we should make sure that the relative proportion of color channels is preserved so that the colors are not washed out.
 +
 +Considering that the luminance is calculated as
 +
 +\[lum = 0.2126 * R + 0.7152 * G + 0.0722 * B\]
 +
 +Further consider that the brightness is simply a "boost" to RGB components, or in other words: gains. And as such all that is needed is to add the brightness \(br\) proportionally to each channel:
 +
 +\[
 +\begin{bmatrix}
 +R' \\
 +G' \\
 +B'
 +\end{bmatrix}
 +=
 +\begin{bmatrix}
 +R + 0.2126 * br \\
 +G + 0.7152 * br \\
 +B + 0.0722 * br
 +\end{bmatrix}
 +\]
 +
 +Of course when implemented on FPGA the preference is to use integer arithmetic, which can be easily achieved by an approximation, considering that \(2^{10} = 1024 \approx 1000\) (which is "good enough" for us:
 +
 +\[
 +\begin{bmatrix}
 +R' \\
 +G' \\
 +B'
 +\end{bmatrix}
 ++=
 +\begin{bmatrix}
 +213 * br \\
 +715 * br \\
 +72 * br
 +\end{bmatrix} / 1024
 +\]
 +
 +===== In HSL color space =====
 +When using the HSL color space the adjustment is as simple as elementary school's arithmetic operation. Namely - just a simple addition.
  
 With that the implementation of the Brightness adjustment can be as simple as the following (where the "luma", or brightness component \(\in[0..100]%%\)): With that the implementation of the Brightness adjustment can be as simple as the following (where the "luma", or brightness component \(\in[0..100]%%\)):

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