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--- isp:ccm [2021/01/27 23:40] – Igor Yefmov
+++ isp:ccm [2022/04/04 23:32] – external edit 127.0.0.1
@@ Line 10: / Line 10: @@
 ===== CCM =====
-Color Correction Matrix is often used as an "add-on" matrix during YUV->RGB conversion. In our case, since the de-bayering and RGB->YUV conversions happen literally on opposite sides of the imaging pipeline, we only use the portion of the corrections designed to compensate for the sensor's cross-talk, converting post-debayer values \(R_0, G_0, B_0\) into \(R, G, B\). Note that the ordering of chroma components is \(BGR\):
+Color Correction Matrix is often used as an "add-on" matrix during YUV->RGB conversion. In our case, since the de-bayering and RGB->YUV conversions happen literally on opposite sides of the imaging pipeline, we only use the portion of the corrections designed to compensate for the sensor's cross-talk, converting post-debayer values \(R_0, G_0, B_0\) into \(R, G, B\):
 \[
- \begin{bmatrix} B & G & R\end{bmatrix}
+ \begin{bmatrix} R & G & B\end{bmatrix}
  =
  \begin{bmatrix}
@@ Line 22: / Line 22: @@
  \cdot
  \begin{bmatrix}
- B_0 \\
+ R_0 \\
  G_0 \\
- R_0
+ B_0
  \end{bmatrix}
 \]
+Regular linear algebra rules apply, of course. The calculation itself (once expanded) looks like this:
+\[
+R = CCM_{00} * R_0 + CCM_{01} * G_0 + CCM_{02} * B_0 \\
+G = CCM_{10} * R_0 + CCM_{11} * G_0 + CCM_{12} * B_0 \\
+B = CCM_{20} * R_0 + CCM_{21} * G_0 + CCM_{22} * B_0
+\]
 ===== 3x3 -> 4x4 =====
 Industry papers on CCM use a \(3\times3\) matrix yet we tried to do a full \(4\times4\) so there was a need to find a way to convert from one to another (and also from an RGGB into BGGR ordering). Here's an [[https://math.stackexchange.com/questions/3957955/ccm-3x3-into-4x4-image-processing|article on Math StackExchange]] on that subject.

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