How do I remove the background (specifically the vignette) from this image without removing the particles of sand?

Question

Samuel Nathan Bernas 2023-7-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2000208-how-do-i-remove-the-background-specifically-the-vignette-from-this-image-without-removing-the-part

评论： Samuel Nathan Bernas 2023-7-25

I am doing research where my goal is to remove out of focus particles of sand, and count in focus particles of sand that I capture in lab. I am currently trying to isolate the objects using imgradient but the vignette hinders the ability to distinguish a gradient. I would like to remove the backround vignette as it disrupts the ability to count the particles. I would appreciate any help!

Here's my code (readPGRaw is code we wrote in order to read in our raw images):

filename= '/Users/sammybuckets/Documents/SandTests/S5_2023-07-18-193451-0000.raw';
ubit= 8;
size= [2448 2048 1];
I = readPGRaw(filename,ubit,size);

figure
G= imgradient(I);
J= G>110;
imagesc(J)
axis image
colormap gray
[JV, JU]= find(J);
hold on
plot(JU,JV,'.')

se = strel('disk',15);
closeJ = imclose(J,se);
[JVC, JUC]= find(closeJ);
plot(JUC,JVC,'.')
plot(JU,JV,'.')

BW2 = imfill(closeJ,'holes');
figure
imshow(BW2)
title('Filled Image')

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Answer 1

Image Analyst 2023-7-25

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2000208-how-do-i-remove-the-background-specifically-the-vignette-from-this-image-without-removing-the-part#answer_1278188

Your best bet is to take a separate, blank shot with no particles in the field of view and then divide your particle images by that blank image. Then you can just use a simple fixed global threshold. Attached is a demo.