Why imnoise function gives pictures with larger size than original image?

Question

Seyed Mousavikia 2021-10-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1466469-why-imnoise-function-gives-pictures-with-larger-size-than-original-image

评论： Walter Roberson 2021-10-11

I have a dataset and after addding noise to images I write them using imwrite function to store them in my data set, but after looking at the generated pictures I see that their size are 2 or 3 times larger than original image, I thought they should be nearly same size(for example my original image is 322KB but my same image + gaussian noise is 780KB ... Can somone explain why?

Here is my code:

%%Speckle
var_speckle=0.05;
%%Salt & Pepper
d=0.05;
%%Gaussian
m=0;
var_gauss=0.01;
%%%%%%%%%%%%%%%
x=0;
imagefiles = dir('*.png');      
nfiles = length(imagefiles);    % Number of files found
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    currentimage = imread(currentfilename);
    %%currentimage = rgb2gray(currentimage);
    %%adjusted = imadjust(currentimage);
    gaussian = imnoise(currentimage,'gaussian',m,var_gauss);
    poisson = imnoise(currentimage,'poisson');
    salt = imnoise(currentimage,'salt & pepper',d);
    speckle = imnoise(currentimage,'speckle',var_speckle);
    imwrite(gaussian,'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'gaussian.png','WriteMode','append')
    imwrite(poisson,'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'poisson.png','WriteMode','append')
    imwrite(salt,'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'salt.png','WriteMode','append')
    imwrite(speckle,'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'speckle.png','WriteMode','append')
    x=x+1;
end

4 个评论
显示 2更早的评论隐藏 2更早的评论

Geoff Hayes 2021-10-4

@Seyed Mousavikia try comparing (usng the debugger) the currentImage and the gaussian image. Do both have the same dimension? Do both have the same data type? If so, then both images should be the same size when saved to file.

Seyed Mousavikia 2021-10-4

Ok I will try Geoff.. yes they have both same size and same data type

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

yanqi liu 2021-10-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1466469-why-imnoise-function-gives-pictures-with-larger-size-than-original-image#answer_804636

imwrite(mat2gray(gaussian),'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'gaussian.png','WriteMode','append')

imwrite(mat2gray(poisson),'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'poisson.png','WriteMode','append')

imwrite(mat2gray(salt),'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'salt.png','WriteMode','append')

imwrite(mat2gray(speckle),'C:\Users\dell\Desktop\Shabake_Asli\Dataset\ExtendedDataset\Mirror\SleepNoiseAddMirror\'+string(x)+'speckle.png','WriteMode','append')

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。

Answer 2

Walter Roberson 2021-10-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1466469-why-imnoise-function-gives-pictures-with-larger-size-than-original-image#answer_804671

编辑：Walter Roberson 2021-10-11

png file size depends on the choice of filter algorithms. imwrite does not offer any choice and is not necessarily offering the best filters.

https://en.m.wikipedia.org/wiki/Portable_Network_Graphics

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。

Answer 3

Seyed Mousavikia 2021-10-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1466469-why-imnoise-function-gives-pictures-with-larger-size-than-original-image#answer_805956

编辑：Seyed Mousavikia 2021-10-11

So you mean if I change the format of my images (e.g jpeg format) the imwrite result will be same size as original images?

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Walter Roberson 2021-10-11

No. .jpeg uses a different compression method that loses information. Comparing the file size it can create with the file size of PNG (which does not lose information) is not fair.

You might not be able to use imwrite() to get back the original file size.

I would suggest to you that immediately after you imread() the original file, that you imwrite() it out to a new name as a PNG file. And then later you would compare the size of the written image-with-noise PNG to the size of the PNG you saved. It might not be the same size as the original PNG file, but the two would have been saved with the same compression algorithm so it would be fair to compare them.

请先登录，再进行评论。