用浮点值写一个图像 [英] Writing an image with floating point values

问题描述

我的代码读取RGB图像，处理它产生浮点结果。如何在Matlab 7.6.0（R2008a）中将这些值作为图像写入，保持这些浮点值？

解决方案

实际上可以适应64位的像素数据（即，表示一个像素数据所需要的位数）rel =， nofollow noreferrer>双精度浮点值）转换为某些图像格式，具体来说就是 PNG 。而且你甚至可以准确地恢复数据。关键是将所有内容编码为 uint16 的值，并使用 Truecolor RGB图像（16位数据的3个颜色平面）以及alpha透明度图（另外16位）。这是编码步骤：

pre $ data $ rand（4）; ％只是一些示例数据，一个小的4×4矩阵
hexData = num2hex（data（:)）; ％获取每个像素的16位十六进制代码
C = mat2cell（hexData，numel（data），[4 4 4 4]）; ％将十六进制代码拆分为4组4
C = cellfun（@（c）{uint16（hex2dec（c））}，C）; ％将每个十六进制值转换为16位整数
colorData = reshape（[C {1：3}]，[size（data）3]）; ％4×4×3 uint16颜色数据
alphaData = reshape（C {4}，size（data））; ％4-by-4 uint16 alpha数据
imwrite（colorData，'double_data.png'，'Alpha'，alphaData）; ％保存图片

您现在拥有一个有效的图片文件，你看它。现在，你可以这样解码：

  [imColor，〜，imAlpha] = imread（'double_data.png'）; ％load image 
 imSize = size（imColor）; ％获取图​​像大小
 imHex = [dec2hex（imColor（:,, 1））...％将每个uint16转换为十六进制并连接
 dec2hex（imColor（:,, 2））。 。
 dec2hex（imColor（:,：，3））... 
 dec2hex（imAlpha）]; 
 imdata = reshape（hex2num（imHex），imSize（1：2））; ％重现数据
  

以及相等检查：

 >> isequal（imdata，data）
 
 ans = 
 
逻辑
 
 1％这是相同的！ 
  

My code reads an RGB image, processing it to produce floating-point results. How can I write these values as an image, maintaining these floating-point values, in Matlab 7.6.0 (R2008a)?

解决方案

It is actually possible to fit 64 bits of pixel data (i.e. the number of bits needed to represent a double-precision floating-point value) into certain image formats, specifically a PNG. And you can even recover the data exactly. The key is to encode everything as uint16 values and use a Truecolor RGB image (3 color planes of 16 bit data) along with an alpha transparency map (another 16 bits). Here's the encoding step:

data = rand(4);              % Just some sample data, a small 4-by-4 matrix
hexData = num2hex(data(:));  % Get the 16 digit hex codes for each pixel
C = mat2cell(hexData, numel(data), [4 4 4 4]);  % Split the hex codes into 4 groups of 4
C = cellfun(@(c) {uint16(hex2dec(c))}, C);  % Convert each hex value into a 16 bit integer
colorData = reshape([C{1:3}], [size(data) 3]);  % 4-by-4-by-3 uint16 color data
alphaData = reshape(C{4}, size(data));          % 4-by-4 uint16 alpha data
imwrite(colorData, 'double_data.png', 'Alpha', alphaData);  % Save image

You now have a valid image file, although it'll probably looks like random garbage if you view it. Now, you can decode it like so:

[imColor, ~, imAlpha] = imread('double_data.png');  % Load image
imSize = size(imColor);  % Get image size
imHex = [dec2hex(imColor(:, :, 1)) ...  % Convert each uint16 to hex and concatenate
         dec2hex(imColor(:, :, 2)) ...
         dec2hex(imColor(:, :, 3)) ...
         dec2hex(imAlpha)];
imdata = reshape(hex2num(imHex), imSize(1:2));  % Reproduce data

And an equality check:

>> isequal(imdata, data)

ans =

  logical

   1           % it's the same!

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