Why I do I get different results when I used jaccard Index with png format than with jpg format?

Question

yasmin ismail 2023-10-8

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2030739-why-i-do-i-get-different-results-when-i-used-jaccard-index-with-png-format-than-with-jpg-format

评论： yasmin ismail 2023-10-10

When I applied the following:

A = logical(imread('R7001-21.png'));
BW_groundTruth =logical(imread('gT7001_21.png'));
similarity = jaccard(A, BW_groundTruth)

I got:

>> GT_jac_index

similarity =

0.9952

While when I applied

A = logical(imread('R7001-21.jpg'));
BW_groundTruth =logical(imread('gT7001_21.jpg'));
similarity = jaccard(A, BW_groundTruth)

I got:

>> GT_jac_index

similarity =

0.8843

Why? And is it better to use png format images?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2023-10-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2030739-why-i-do-i-get-different-results-when-i-used-jaccard-index-with-png-format-than-with-jpg-format#answer_1328834

Both sets of code use the PNG versions.

In general you should not use JPG files for image analysis, unless you're specifically doing research on compression and how lousy JPG is compared to other methods.

It is better to use PNG because it is a loasless compression and does not change values or introduce artifacts (such as contouring/posterization, edge blurring, etc.) like JPG does.

7 个评论
显示 5更早的评论隐藏 5更早的评论

Image Analyst 2023-10-10

在 MATLAB Online 中打开

The images are different. Not all the pixels are the same so the jaccard index will not be 1.

fileName1 = 'R7001-21.png';
fileName2 = 'gT7001_21.png';
fileName3 = 'R7001-21.jpg';
fileName4 = 'gT7001_21.jpg';
% Read in all files:
image1 = imread(fileName1);
image2 = imread(fileName2);
image3 = imread(fileName3);
image4 = imread(fileName4);
% Take green channel of all of them.
image1 = image1(:, :, 2);
image2 = image2(:, :, 2);
image3 = image3(:, :, 2);
image4 = image4(:, :, 2);
% See how many pixels are different between the two.
diffImage = imabsdiff(image1, image2);
fprintf('Image 1 differs from image2 by %d pixels.\n', nnz(diffImage));
Image 1 differs from image2 by 133 pixels.
diffImage = imabsdiff(image1, image3);
fprintf('Image 1 differs from image3 by %d pixels.\n', nnz(diffImage));
Image 1 differs from image3 by 133 pixels.
diffImage = imabsdiff(image1, image4);
fprintf('Image 1 differs from image4 by %d pixels.\n', nnz(diffImage));
Image 1 differs from image4 by 3238 pixels.
diffImage = imabsdiff(image2, image3);
fprintf('Image2 differs from image3 by %d pixels.\n', nnz(diffImage));
Image2 differs from image3 by 0 pixels.
diffImage = imabsdiff(image2, image4);
fprintf('Image2 differs from image4 by %d pixels.\n', nnz(diffImage));
Image2 differs from image4 by 3263 pixels.
diffImage = imabsdiff(image3, image4);
fprintf('Image3 differs from image4 by %d pixels.\n', nnz(diffImage));
Image3 differs from image4 by 3263 pixels.
% Compare filenames 1 and 2
testImage = logical(image1);
BW_groundTruth = logical(image2);
similarity = jaccard(testImage, BW_groundTruth)
similarity = 0.9952
% Compare filenames 3 and 4
testImage = logical(image3);
BW_groundTruth = logical(image4);
similarity = jaccard(testImage, BW_groundTruth)
similarity = 0.8843
% Compare filenames 1 and 3
testImage = logical(image1);
BW_groundTruth = logical(image3);
similarity = jaccard(testImage, BW_groundTruth)
similarity = 0.9952
% Compare filenames 2 and 4
testImage = logical(image2);
BW_groundTruth = logical(image4);
similarity = jaccard(testImage, BW_groundTruth)
similarity = 0.8843