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imwrite does not work when file extension is given

조회 수: 2 (최근 30일)
Jason Johnson
Jason Johnson 2021년 7월 13일
댓글: Jason Johnson 2021년 7월 14일
I am trying to create a folder of images using imwrite in a for loop. All previous problems with imwrite seem to stem from a permission problem or incorrect file naming. I have ensured my file permissions are correct in windows and I cannot find any error in my file naming. I first create a folder path using mkdir. Then, within a loop I define my image and its name, then save it using imwrite. Within imwrite I use fullfile(path,name) to create a correct file name at the location I want.
Here is my simple code
%% Greyscale shrinkage control structures
gval = 0.5;
grey = repelem(gval,95);
grey = uint8(grey*255);
wc = 608/2;
hc = 684/2;
w = 100;
h = 200;
path = fullfile(pwd,'grey_beams',['grey_shrinkage_control_' 'grey_val_' strrep(num2str(gval),'.','-')]);
mkdir(path)
for i = 1:96
I = uint8(zeros(684,608));
if i > 3 && i < 96
I(hc-h:hc+h,wc:wc+w) = 255;
I(hc-h:hc+h,wc-w:wc-1) = grey(i);
elseif i <= 3
I(hc-h:hc+h,wc-250:wc+250) = 255;
end
name = ['pattern_' sprintf('%03d',i-1) '.bmp']
imwrite(I,fullfile(path,name),'bmp')
end
This gives me the following error for the first iteration of the loop
% Error using imwrite (line 548)
% Unable to open file "C:\Users\Jason Johnson\Documents\Purdue\Purdue_Research\Polymerization
% Model\Code\Spatiotemporal Code\grey_beams\grey_shrinkage_control_grey_val_0-5\pattern_000.bmp" for
% writing. You might not have write permission.
%
% Error in grey_shrinkage_tuning (line 26)
% imwrite(I,fullfile(path,name),'bmp')
This code works perfectly when I delete '.bmp' from name on line 25. But, then it saves the files with no particular format, when, instead, I need them to be a bitmap.
Furthermore, the given code will work if I insert
edit(fullfile(path,name))
before the imwrite on line 26. However, then the code is slowed down significantly, and I have 96 tabs in the editor window that I have to close manually.
What is causing this file permission error?
  댓글 수: 5
Jason Johnson
Jason Johnson 2021년 7월 13일
Simon,
I have checked to make sure the files do not exist. I tried this code to ensure the file does not exist prior to using imwrite,
if exist(fullfile(path,name))
delete(fullfile(path,name))
end
This did not make a difference. I also tried using fopen with 'w' permission to create a file in case imwrite was having trouble creating the file for some reason. When I did this I just got a permission denied response from fopen. Then if I go back and check if the file exists it still does not. I am on a personal computer where all users have administrative access.
dpb
dpb 2021년 7월 13일
편집: dpb 2021년 7월 13일
The deal about only the extension being on the filename causing the problem convinces me it is something of the sort if you can otherwise access the subdirectory.
It isn't imwrite that's the culprit if fopen() also has the problem--that's tied in to the OS and file system and permissions for the specific file(s).

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채택된 답변

Jan
Jan 2021년 7월 13일
편집: Jan 2021년 7월 13일
Do not use "path" as name of a variable, because this shadows an important Matlab command. This does run usually, but during debugging you can get serious troubles.
Relying on this current directory is fragile, because any callback of a timer or GUI can change it unexpectedly. So instead of useing pwd() (which does nothing than callin cd() by the way), provide an absolute path.
"then it saves the files with no particular format" - there are no files without a format. imwrite uses the format from the file name, if you omit the specifier 'bmp' to determine the format.
Use this code for checking the existence of the file:
gval = 0.5;
grey = repmat(uint8(gval * 255), 1, 95);
wc = 608/2;
hc = 684/2;
w = 100;
h = 200;
base = 'C:\Your\Base\Path';
folder = fullfile(base, 'grey_beams', ...
['grey_shrinkage_control_grey_val_', strrep(num2str(gval), '.', '-')]);
mkdir(folder)
for i = 1:96
I = zeros(684,608, 'uint8');
if i <= 3
I(hc-h:hc+h, wc-250:wc+250) = 255;
elseif i < 96
I(hc-h:hc+h, wc:wc+w) = 255;
I(hc-h:hc+h, wc-w:wc-1) = grey(i);
end
file = fullfile(folder, sprintf('pattern_%03d.bmp', i-1));
if isfile(file)
error('File is existing already: %s', file);
end
imwrite(I, file, 'bmp');
% ^^^^^ this is optional
end
What do you observe?
I've inserted some simplifications in the code.
  댓글 수: 8
Jason Johnson
Jason Johnson 2021년 7월 14일
That is correct. Pausing my antivirus software solves the issue!
Jason Johnson
Jason Johnson 2021년 7월 14일
For some reason my antivirus software had decided to designate MATLAB as a shady app. Removing this designation has solved my issue. Thank you Jan for leading me to this issue!

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추가 답변 (2개)

Image Analyst
Image Analyst 2021년 7월 14일
I ran the original code and it ran fine - no errors. Nonetheless, I made some improvements in it:
fprintf('Beginning to run %s.m ...\n', mfilename);
%% Greyscale shrinkage control structures
gval = 0.5;
grey = repelem(gval,95);
grey = uint8(grey*255);
wc = 608/2;
hc = 684/2;
w = 100;
h = 200;
folder = fullfile(pwd,'grey_beams', ['grey_shrinkage_control_', 'grey_val_', strrep(num2str(gval),'.','-')]);
if ~isfolder(folder)
mkdir(folder);
end
for k = 1 : 96
grayImage = uint8(zeros(684,608));
if k > 3 && k < 96
grayImage(hc-h:hc+h,wc:wc+w) = 255;
grayImage(hc-h:hc+h,wc-w:wc-1) = grey(k);
elseif k <= 3
grayImage(hc-h:hc+h,wc-250:wc+250) = 255;
end
baseFileName = sprintf('pattern_%03d.bmp', k-1);
fullFileName = fullfile(folder, baseFileName);
fprintf('Writing %s\n', fullFileName);
imwrite(grayImage, fullFileName);
end
fprintf('Done running %s.m.\n', mfilename);
What if you try using PNG images? PNG is a much more common format these days than BMP.
  댓글 수: 1
Jason Johnson
Jason Johnson 2021년 7월 14일
Image Analyst,
Thank you for improving my code. My use for these images requires a BMP format. But regardless, changing the format does not seem to solve the issue. Unfortunately, it seems to be specfic to my machine.

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Jason Johnson
Jason Johnson 2021년 7월 14일
The code presented in the original question works well on other machines. Additionally, changing the file name and location seems to have no effect on the issue. Both fopen and imwrite are unable to write to a file anytime a file extension is included in the name.
Does anyone have any ideas on doing some debugging more specific to file management on my machine, whether that be through MATLAB or Windows?

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