intensity correction in images

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Turbulence Analysis 2021-5-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/844375-intensity-correction-in-images

评论： Turbulence Analysis 2021-6-24

采纳的回答： Image Analyst

Raw image.bmp

Hi,

I intend to correct the intensity in the images which arises due to the non uniformity in the illumination source.

As illustrated in the attched image, due to presence of inhomogeneity associated with the illumination source, the intensity is maximum at left and right side, however it is low on top and bottom. Now I intend to have uniform intensity through out. Is there any way out to achieve this ??

I tried with the normalize option e.g., But I am not succesful ..

normalize ( image data, 'range')

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Answer 1

Image Analyst 2021-5-31

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https://ww2.mathworks.cn/matlabcentral/answers/844375-intensity-correction-in-images#answer_713685

在 MATLAB Online 中打开

If that is your illumination source, you need to convert that to a percentage image and then divide your test images by the percentage image.

maxValue = max(illuminationImage(:))
percentageImage = double(illuminationImage) / maxValue;
correctedImage = double(testImage) ./ percentageImage;

Rationale: If the image only has 90% as many photons hitting the scene there, you'd need to divide by 0.9 there to bring it up to the intensity it should have (the intensity it would have if it were illuminated by the full max intensity).

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Image Analyst 2021-6-1

编辑：Image Analyst 2021-6-1

在 MATLAB Online 中打开

I'm not sure I understand.

% Demo by Image Analyst.
clc;    % Clear the command window.
fprintf('Beginning to run %s.m ...\n', mfilename);
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
load('illuminationImage.mat')
load('testImage.mat')
nexttile;
imshow(illuminationImage, []);
title('Illumination Image', 'FontSize', fontSize);
nexttile;
imshow(testImage, []);
title('Test Image', 'FontSize', fontSize);
maxValue = max(illuminationImage(:))
percentageImage = double(illuminationImage) / maxValue;
nexttile;
imshow(percentageImage, []);
title('Percentage Image', 'FontSize', fontSize);
correctedImage = double(testImage) ./ percentageImage;
nexttile;
imshow(correctedImage, []);
title('Corrected Image', 'FontSize', fontSize);
fprintf('Done running %s.m\n', mfilename);

Is the illumination image an image of the laser scanning the flat, uniform white or gray sheet? Well that looks pretty uniform. And is the image with the circle the image with a circular object in there? Is the circular object flat or 3-D? If it's 3-D then if it's closer to the laser it could reflect more brightly of course. If it's flat, then the reflectance should be the reflectance of the object, modified by the spatial variation of the laser and lens (but that looks pretty uniform to me)>

Turbulence Analysis 2021-6-1

Yes, the illumination image is just recorded only with the laser sheet ON but without the presence of subject.. The laser sheet is flat

And I understod your point on the reflectance, but here the laser sheet profile itself not uniform. The intensity of the laser sheet is something similar to the one shown here (please see sheet profile.bmp). For instance, the portion of the subject illuminated by sheet region of A, C shows higher intensity , However, the decrease in intensity of laser sheet at region B results in lesser intesnity on the subject.

For e.g. In the test image you have shown, top and bottom portion is illuminated by region A, C of laser that's why it is brighter than middle portion that is illuminated by part B of the laser sheet. Hence, my idea is to correct this non uniformity in the intensity on the testImage. I tried as normalize option in matlab, I have attached the image obtained before and after normalization..

normalize ( testImage , 'range');

I hope this clarifies.. Please do let me know for adiitional info's...

Turbulence Analysis 2021-6-2

Here the subject is actually a flame. Just imagine a candle flame, I am passing a laser sheet horizontally into the flame, say 5 mm above the candle. The insident laser beam will generate the fluorescence signal when the flame is present, and I am captuirng this fluoresecnce signal in the camera. Camera is placed on the top of laser laser sheet. Please have a look at the attached sketch..

The fluorescence signal is present only when the subject i.e. flame is present. Here, the attached image with ring shape is the one captured with the presence of subject. The another one is just black, because that is recorded in absence of subject i.e. flame , hence no fluorescence signal.

Here, the intensity of the generated fluoresecnce signal is directly proportional to the energy of the insident beam energy. This the reason why in the ring shaped image, some portion got higher intensity while other being lesser. This arises due to gausian profile of laser sheet. I attaching the .mat file of the ring image for your beter reference.

I guess it may be better to correct the intensity if we somehow have the sheet profile, however, the same is limited in the present configuration. Please let me know for additional info...

Image Analyst 2021-6-6

在 MATLAB Online 中打开

No. It would be something like

mask = grayImage > someThresholdValue;
maxValue = max(grayImage(:))
grayImage(mask) = maxValue; % Set everything in the ring equal to the max value.

Turbulence Analysis 2021-6-24

Appologies for being late in responding.. Yes, I am getting the desired results....

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Answer 2

Turbulence Analysis 2021-5-31

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https://ww2.mathworks.cn/matlabcentral/answers/844375-intensity-correction-in-images#answer_713810

Many thanks..

I have tried, but didn't get the desired results.. I have attached the corrected image, which I have got

I have attached test image, illumination image mat files for your reference.

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Amit 2021-6-5

You need to normalize intensity of all images and then you segmentation of region of intest will be become uniform.

Adjusting contrast of images so as to cover complete dynamic range of intensity of all pixels.

Please send all of your database images as zip file to amit.kenjale@gmail.com, I will try our some code that will work for all of your images.

Turbulence Analysis 2021-6-5

My image.mat

Amit,

Thanks for the suggestion. I have attched the .mat file of the sample image here... Please let me know if you get any issues while accessing...

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intensity correction in images

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