Question

我正在将YUV420转换为RGB，但是图像颜色效果不佳。本来我自己的文件是10位的。最初，我从8位文件开始。

我正在使用下面的代码读取YUV420图像并转换为RGB。因为我有YUV420.YUV图像文件，但是该代码用于视频，所以我只读取1帧。然后，我得到YUV的全尺寸为Y，但U和V为一半，如Wikipedia所述。然后，我将图像调整为图像的完整大小，并将YUV应用于RGB转换。但是RGB图像的颜色不正确。我已附加文件，以便您可以运行并查看问题所在。这是YUV文件tulips_yuv420_inter_planar_qcif.yuv。

我还有两个问题；

首先，一帧“流”的大小应等于1.5 * Y的大小，但是无论我使用uint8还是uint16来读取文件，它都非常大。

第二，如果我有10位YUV420文件，如何修改此代码以显示正确的RGB。

fname = 'tulips_yuv420_inter_planar_qcif.yuv';
width  = 176;
height = 144;
nFrame=1;
fid = fopen(fname,'r');           % Open the video file
stream = fread(fid,'uint8');    % uint16
% stream = fread(fid);    % uint8

length = 1.5 * width * height;  % Length of a single frame

y = double(zeros(height,   width,   nFrame));
u = double(zeros(height/2, width/2, nFrame));
v = double(zeros(height/2, width/2, nFrame));

for iFrame = 1:nFrame

   frame = stream((iFrame-1)*length+1:iFrame*length);

   % Y component of the frame
   yImage = reshape(frame(1:width*height), width, height)';
   % U component of the frame
   uImage = reshape(frame(width*height+1:1.25*width*height), width/2, height/2)';
   % V component of the frame
   vImage = reshape(frame(1.25*width*height+1:1.5*width*height), width/2, height/2)';

   y(:,:,iFrame) = double(yImage);
   u(:,:,iFrame) = double(uImage);
   v(:,:,iFrame) = double(vImage);

end
u=imresize(u,size(y),'bicubic');
v=imresize(v,size(y),'bicubic');
yuv=cat(3,y,u,v);
T = [1,0,1.28033;1,-0.21482,-0.38059;1,2.12798,0];


RGB(:,:,1) = T(1)*yuv(:,:,1) + T(4)*yuv(:,:,2) + T(7)*yuv(:,:,3) ;
RGB(:,:,2) = T(2)*yuv(:,:,1) + T(5)*yuv(:,:,2) + T(8)*yuv(:,:,3) ;
RGB(:,:,3) = T(3)*yuv(:,:,1) + T(6)*yuv(:,:,2) + T(9)*yuv(:,:,3) ;

figure,imshow(uint8(RGB))

Answer 1

示例文件是8位（而不是10位），并且存储格式比较棘手。

该工具允许您选择格式。
合适的格式如下：

帧分为两个字段-上字段和下字段（隔行格式）。
每个文件的分辨率为176x72。
由于格式为YUV420，因此U和V字段的大小为88x36。

该代码示例使用以下阶段：

读取Y，U和V的高位文件（每个元素8位）。
读取Y，U和V的下部字段。
交织上场和下场。
将U和V上采样到Y的大小。
将YUV转换为RGB（使用现有的MATLAB函数ycbcr2rgb）。

下面的代码示例读取第一帧并转换为RGB：

fname = 'tulips_yuv420_inter_planar_qcif.yuv';
width  = 176;
height = 144;
fid = fopen(fname, 'r');           % Open the video file

Y0 = (fread(fid, [width, height/2], 'uint8'))';     %Read upper field of Y plane
U0 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of Y plane
V0 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read upper field of U plane

Y1 = (fread(fid, [width, height/2], 'uint8'))';     %Read upper field of Y plane
U1 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of U plane
V1 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of V plane

fclose(fid);

%Interleave upper and lower fields
Y = zeros(height, width);
Y(1:2:end, :) = Y0;
Y(2:2:end, :) = Y1;

U = zeros(height/2, width/2);
U(1:2:end, :) = U0;
U(2:2:end, :) = U1;

V = zeros(height/2, width/2);
V(1:2:end, :) = V0;
V(2:2:end, :) = V1;

U = imresize(U, size(Y), 'bicubic');
V = imresize(V, size(Y), 'bicubic');
YUV = cat(3, Y, U, V);

%Convert YUV to RGB (MATLAB function ycbcr2rgb uses BT.601 conversion formula).
RGB = ycbcr2rgb(uint8(YUV));

figure,imshow(RGB)

结果：

读取10位YUV420：

假设：

每个10位分量存储在2个字节中（无“位打包”）。
数据存储在每个字节的下部（每个uint16元素的值都在[0，1023]范围内）。
存储格式与uint8示例是相同的非标准隔行扫描格式。

从8位样本中构建10位YUV420样本文件（用于测试的单个帧）：
以下代码在8位样本中构建了10位样本（将范围从uint8中存储的8位扩展为uint16中存储的10位）。

fname = 'tulips_yuv420_inter_planar_qcif.yuv';
width  = 176;
height = 144;
fid = fopen(fname, 'r');           % Open the video file
Y0 = (fread(fid, [width, height/2], 'uint8'))';     %Read upper field of Y plane
U0 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of Y plane
V0 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read upper field of U plane
Y1 = (fread(fid, [width, height/2], 'uint8'))';     %Read upper field of Y plane
U1 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of U plane
V1 = (fread(fid, [width/2, height/4], 'uint8'))';   %Read lower field of V plane
fclose(fid);

fid = fopen('10bits__tulips_yuv420_inter_planar_qcif.yuv', 'w');           % Open for writing
fwrite(fid, uint16(Y0'*(1023/255)), 'uint16'); %1023 = 2^10-1, and 255 = 2^8-1
fwrite(fid, uint16(U0'*(1023/255)), 'uint16');
fwrite(fid, uint16(V0'*(1023/255)), 'uint16');
fwrite(fid, uint16(Y1'*(1023/255)), 'uint16');
fwrite(fid, uint16(U1'*(1023/255)), 'uint16');
fwrite(fid, uint16(V1'*(1023/255)), 'uint16');
fclose(fid);

读取10位YUV420
以下代码读取10位YUV420的单帧（假设匹配的列表）：

fname = '10bits__tulips_yuv420_inter_planar_qcif.yuv';
width  = 176;
height = 144;
fid = fopen(fname, 'r');           % Open the video file

Y0 = (fread(fid, [width, height/2], 'uint16'))';     %Read upper field of Y plane
U0 = (fread(fid, [width/2, height/4], 'uint16'))';   %Read lower field of Y plane
V0 = (fread(fid, [width/2, height/4], 'uint16'))';   %Read upper field of U plane

Y1 = (fread(fid, [width, height/2], 'uint16'))';     %Read upper field of Y plane
U1 = (fread(fid, [width/2, height/4], 'uint16'))';   %Read lower field of U plane
V1 = (fread(fid, [width/2, height/4], 'uint16'))';   %Read lower field of V plane

fclose(fid);

%Interleave upper and lower fields
Y = zeros(height, width);
Y(1:2:end, :) = Y0;
Y(2:2:end, :) = Y1;

U = zeros(height/2, width/2);
U(1:2:end, :) = U0;
U(2:2:end, :) = U1;

V = zeros(height/2, width/2);
V(1:2:end, :) = V0;
V(2:2:end, :) = V1;

U = imresize(U, size(Y), 'bicubic');
V = imresize(V, size(Y), 'bicubic');
YUV = cat(3, Y, U, V);

%Convert elements range from [0, 1023] to range [0, 1] (MATLAB function ycbcr2rgb supports doubles in range [0, 1]).
YUV = YUV/1023; %1023 applies 10 bits range. 2^10-1 = 1023

%Convet YUV to RGB (MATLAB function ycbcr2rgb uses BT.601 conversion formula).
RGB = ycbcr2rgb(YUV);

%Convert from double to uint8 (from range [0, 1] to range [0, 255]).
RGB = im2uint8(RGB);

figure,imshow(RGB)

注意：
代码YUV = YUV/1023将“ 10位”格式转换为[0，1] double格式。
使用转换是因为ycbcr2rgb不支持10位输入。

计算文件大小：
您是正确的：“一帧的大小等于1.5 * Y的大小”。
假设在2个字节中存储了10位分量，则Y的大小为宽度*高度* 2，一帧的大小为宽度*高度* 3。

10位YUV420到RGB的转换

1 个答案: