去马赛克（Demosaic）一

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前言

\quad\quad 关于为什么要做去马赛克参加博文Understanding ISP Pipeline – Demosaicking。简单来说就是当前使用较多的CCD和CMOS sensor用的是Bayer CFA格式，或者Bayer mosaic格式，支持这种格式的成像器件（包括CCD和CMOS两种）输出的数据格式俗称RAW格式，特点是每个像素只提供RGB三种颜色中的一种，另外两种颜色需要后续处理环节中通过一定的软件算法进行插值补全。

去马赛克算法

参考博文ISP算法简述与逻辑实现-demosaic和ISP图像处理之Demosaic算法及相关

双线性插值

• R23 = (R13+R33)/2
• B23 = (B22+B24)/2

R通道上GB插值，以R33为例，

• G33 = (G23+G32+G34+G43)/4
• B33 = (B22+B24+B42+B44)/4

B通道上的RG插值，以B24为例

• R24 = (R13+R15+R33+R35)/4
• B24 = (G14+G23+G25+G34)/4

function imDst = Demosaic_bilinear(bayer,pattern) [H,W] = size(bayer); imDst = zeros(H,W,3); g1 = [0 1/4 0; 1/4 0 1/4; 0 1/4 0]; g2 = [1/4 0 1/4; 0 0 0; 1/4 0 1/4]; h = [0.5 0 0.5]; tmp1 = conv2(bayer,g1,'same'); tmp2 = conv2(bayer,g2,'same'); tmp3 = conv2(bayer,h,'same'); tmp4 = conv2(bayer,h','same'); switch pattern case 'grbg' G(1:2:H,1:2:W) = bayer(1:2:H,1:2:W); G(2:2:H,2:2:W) = bayer(2:2:H,2:2:W); G(1:2:H,2:2:W) = tmp1(1:2:H,2:2:W); G(2:2:H,1:2:W) = tmp1(2:2:H,1:2:W); R(1:2:H,2:2:W) = bayer(1:2:H,2:2:W); R(1:2:H,1:2:W) = tmp3(1:2:H,1:2:W); R(2:2:H,2:2:W) = tmp4(2:2:H,2:2:W); R(2:2:H,1:2:W) = tmp2(2:2:H,1:2:W); B(2:2:H,1:2:W) = bayer(2:2:H,1:2:W); B(1:2:H,1:2:W) = tmp4(1:2:H,1:2:W); B(2:2:H,2:2:W) = tmp3(2:2:H,2:2:W); B(1:2:H,2:2:W) = tmp2(1:2:H,2:2:W); case 'gbrg' G(1:2:H,1:2:W) = bayer(1:2:H,1:2:W); G(2:2:H,2:2:W) = bayer(2:2:H,2:2:W); G(1:2:H,2:2:W) = tmp1(1:2:H,2:2:W); G(2:2:H,1:2:W) = tmp1(2:2:H,1:2:W); R(2:2:H,1:2:W) = bayer(2:2:H,1:2:W); R(1:2:H,1:2:W) = tmp4(1:2:H,1:2:W); R(2:2:H,2:2:W) = tmp3(2:2:H,2:2:W); R(1:2:H,2:2:W) = tmp2(1:2:H,2:2:W); B(1:2:H,2:2:W) = bayer(1:2:H,2:2:W); B(1:2:H,1:2:W) = tmp3(1:2:H,1:2:W); B(2:2:H,2:2:W) = tmp4(2:2:H,2:2:W); B(2:2:H,1:2:W) = tmp2(2:2:H,1:2:W); case 'rggb' G(1:2:H,2:2:W) = bayer(1:2:H,2:2:W); G(2:2:H,1:2:W) = bayer(2:2:H,1:2:W); G(1:2:H,1:2:W) = tmp1(1:2:H,1:2:W); G(2:2:H,2:2:W) = tmp1(2:2:H,2:2:W); R(1:2:H,1:2:W) = bayer(1:2:H,1:2:W); R(1:2:H,2:2:W) = tmp3(1:2:H,2:2:W); R(2:2:H,1:2:W) = tmp4(2:2:H,1:2:W); R(2:2:H,2:2:W) = tmp2(2:2:H,2:2:W); B(2:2:H,2:2:W) = bayer(2:2:H,2:2:W); B(1:2:H,2:2:W) = tmp4(1:2:H,2:2:W); B(2:2:H,1:2:W) = tmp3(2:2:H,1:2:W); B(1:2:H,1:2:W) = tmp2(1:2:H,1:2:W); case 'bggr' G(1:2:H,2:2:W) = bayer(1:2:H,2:2:W); G(2:2:H,1:2:W) = bayer(2:2:H,1:2:W); G(1:2:H,1:2:W) = tmp1(1:2:H,1:2:W); G(2:2:H,2:2:W) = tmp1(2:2:H,2:2:W); R(2:2:H,2:2:W) = bayer(2:2:H,2:2:W); R(1:2:H,2:2:W) = tmp4(1:2:H,2:2:W); R(2:2:H,1:2:W) = tmp3(2:2:H,1:2:W); R(1:2:H,1:2:W) = tmp2(1:2:H,1:2:W); B(1:2:H,1:2:W) = bayer(1:2:H,1:2:W); B(1:2:H,2:2:W) = tmp3(1:2:H,2:2:W); B(2:2:H,1:2:W) = tmp4(2:2:H,1:2:W); B(2:2:H,2:2:W) = tmp2(2:2:H,2:2:W); end imDst = cat(3,R,G,B); 

基于色差恒定的插值

色差恒定准则与色比恒定准则都是基于颜色通道之间的相关性，目的都是把颜色通道之间的相关性信息引入颜色插值算法，提高插值的准确性。具体算法参考博文ISP算法简述与逻辑实现-demosaic，算法流程如下：

• 先对G通道进行双线性插值，得到全分辨率的G’通道
• 计算色彩 Kr = G-R 和 Kb = G-B，然后将Kr和Kb进行双线性插值，得到全分辨率的Kr和Kb:
  Kr11 = G’11-R11
  Kb22 = G’22 – R22
  
  
• R = G-Kr, B = G-Kb

function imDst = Demosaic_color_diff(raw_img,pattern) [hei,wid] = size(raw_img); imDst = zeros(hei,wid,3); Kr = zeros(hei,wid); Kb = zeros(hei,wid); bayerPadding = zeros(hei+2,wid+2); bayerPadding(2:hei+1,2:wid+1) = raw_img; bayerPadding(1,:) = bayerPadding(3,:); bayerPadding(hei+2,:) = bayerPadding(hei,:); bayerPadding(:,1) = bayerPadding(:,3); bayerPadding(:,wid+2) = bayerPadding(:,wid); if pattern == 'grbg' % g imDst(1:2:hei,1:2:wid,2) = bayerPadding(2:2:hei+1,2:2:wid+1); imDst(2:2:hei,2:2:wid,2) = bayerPadding(3:2:hei+1,3:2:wid+1); imDst(1:2:hei,2:2:wid,2) = (bayerPadding(1:2:hei,3:2:wid+2)+bayerPadding(3:2:hei+2,3:2:wid+2)+... bayerPadding(2:2:hei+1,2:2:wid+1)+bayerPadding(2:2:hei+1,4:2:wid+2))/4; imDst(2:2:hei,1:2:wid,2) = (bayerPadding(2:2:hei+1,2:2:wid+1)+bayerPadding(4:2:hei+2,2:2:wid+1)+... bayerPadding(3:2:hei+2,1:2:wid)+bayerPadding(3:2:hei+2,3:2:wid+2))/4; % Kr Kb Kr(1:2:hei,2:2:wid) = imDst(1:2:hei,2:2:wid,2) - bayerPadding(2:2:hei+1,3:2:wid+1); Kb(2:2:hei,1:2:wid) = imDst(2:2:hei,1:2:wid,2) - bayerPadding(3:2:hei+2,2:2:wid+1); Kr = Demosaic_bilinear(Kr,pattern); Kr = Kr(:,:,1); Kb = Demosaic_bilinear(Kb,pattern); Kb = Kb(:,:,3); imDst(:,:,1) = imDst(:,:,2) - Kr; imDst(:,:,3) = imDst(:,:,2) - Kb; elseif pattern == 'gbrg' % g imDst(1:2:hei,1:2:wid,2) = bayerPadding(2:2:hei+1,2:2:wid+1); imDst(2:2:hei,2:2:wid,2) = bayerPadding(3:2:hei+1,3:2:wid+1); imDst(1:2:hei,2:2:wid,2) = (bayerPadding(1:2:hei,3:2:wid+2)+bayerPadding(3:2:hei+2,3:2:wid+2)+... bayerPadding(2:2:hei+1,2:2:wid+1)+bayerPadding(2:2:hei+1,4:2:wid+2))/4; imDst(2:2:hei,1:2:wid,2) = (bayerPadding(2:2:hei+1,2:2:wid+1)+bayerPadding(4:2:hei+2,2:2:wid+1)+... bayerPadding(3:2:hei+2,1:2:wid)+bayerPadding(3:2:hei+2,3:2:wid+2))/4; % Kr Kb Kb(1:2:hei,2:2:wid) = imDst(1:2:hei,2:2:wid,2) - bayerPadding(2:2:hei+1,3:2:wid+1); Kr(2:2:hei,1:2:wid) = imDst(2:2:hei,1:2:wid,2) - bayerPadding(3:2:hei+2,2:2:wid+1); Kr = Demosaic_bilinear(Kr,pattern); Kr = Kr(:,:,1); Kb = Demosaic_bilinear(Kb,pattern); Kb = Kb(:,:,3); imDst(:,:,1) = imDst(:,:,2) - Kr; imDst(:,:,3) = imDst(:,:,2) - Kb; elseif pattern == 'rggb' % g imDst(1:2:hei,2:2:wid,2) = bayerPadding(2:2:hei+1,3:2:wid+2); imDst(2:2:hei,1:2:wid,2) = bayerPadding(3:2:hei+2,2:2:wid+1); imDst(1:2:hei,1:2:wid,2) = (bayerPadding(1:2:hei,2:2:wid+1)+bayerPadding(3:2:hei+2,2:2:wid+1)+... bayerPadding(2:2:hei+1,1:2:wid)+bayerPadding(2:2:hei+1,3:2:wid+2))/4; imDst(2:2:hei,2:2:wid,2) = (bayerPadding(2:2:hei+1,3:2:wid+2)+bayerPadding(4:2:hei+2,3:2:wid+2)+... bayerPadding(3:2:hei+2,2:2:wid+1)+bayerPadding(3:2:hei+2,4:2:wid+2))/4; % Kr Kb Kr(1:2:hei,1:2:wid) = imDst(1:2:hei,1:2:wid,2) - bayerPadding(2:2:hei+1,2:2:wid+1); Kb(2:2:hei,2:2:wid) = imDst(2:2:hei,2:2:wid,2) - bayerPadding(3:2:hei+2,3:2:wid+2); Kr = Demosaic_bilinear(Kr,pattern); Kr = Kr(:,:,1); Kb = Demosaic_bilinear(Kb,pattern); Kb = Kb(:,:,3); imDst(:,:,1) = imDst(:,:,2) - Kr; imDst(:,:,3) = imDst(:,:,2) - Kb; elseif pattern == 'bggr' % g imDst(1:2:hei,2:2:wid,2) = bayerPadding(2:2:hei+1,3:2:wid+2); imDst(2:2:hei,1:2:wid,2) = bayerPadding(3:2:hei+2,2:2:wid+1); imDst(1:2:hei,1:2:wid,2) = (bayerPadding(1:2:hei,2:2:wid+1)+bayerPadding(3:2:hei+2,2:2:wid+1)+... bayerPadding(2:2:hei+1,1:2:wid)+bayerPadding(2:2:hei+1,3:2:wid+2))/4; imDst(2:2:hei,2:2:wid,2) = (bayerPadding(2:2:hei+1,3:2:wid+2)+bayerPadding(4:2:hei+2,3:2:wid+2)+... bayerPadding(3:2:hei+2,2:2:wid+1)+bayerPadding(3:2:hei+2,4:2:wid+2))/4; % Kr Kb Kb(1:2:hei,1:2:wid) = imDst(1:2:hei,1:2:wid,2) - bayerPadding(2:2:hei+1,2:2:wid+1); Kr(2:2:hei,2:2:wid) = imDst(2:2:hei,2:2:wid,2) - bayerPadding(3:2:hei+2,3:2:wid+2); Kr = Demosaic_bilinear(Kr,pattern); Kr = Kr(:,:,1); Kb = Demosaic_bilinear(Kb,pattern); Kb = Kb(:,:,3); imDst(:,:,1) = imDst(:,:,2) - Kr; imDst(:,:,3) = imDst(:,:,2) - Kb; end