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# Image illumination correction of arterial contour

Asked by mona on 26 Feb 2013

I have a code which which I am a bit confused on how to optimize in order to make it work for an image http://tinypic.com/view.php?pic=2jdx6g&s=7 since I am not able to modify the function imopen to remove the background illumination in order to obtain clear picture of the coronary vessels. Any suggestion?

## Products

Answer by Image Analyst on 26 Feb 2013

That is not what imopen is supposed to do. If anything it would be imclose() which does a dilation (smear bright stuff over the dark vessels) followed by an erosion (to return enlarged bright things to their original size). But I'd look at the literature to see what people are doing successfully with angiograms rather than spend time implementing something that ends up being really primitive and ineffective. http://iris.usc.edu/Vision-Notes/bibliography/contentsmedical.html#Medical%20Applications,%20CAT,%20MRI,%20Ultrasound,%20Heart%20Models,%20Brain%20Models

Image Analyst on 27 Feb 2013

I don't see imclose() and don't know the purpose of log() and fir1() or any of that code. I thought you just wanted to background correct the images. If you want to discover (-mu*x) of your contrast agent, you just take the log of both images (with and without contrast) and subtract them. If you don't have the image without contrast agent (for some strange reason) then you can estimate it by doing a morphological closing.

The theory says, for the background image

image1 = initialIntensity * exp(-mu1 * x1); % x = thickness

For the image with contrast

image2 = initialIntensity * exp(-mu1 * x1 - mu2 * x2); % x = thickness

So the steps would be

```image2 = imclose(image1, close(15)); % May need to adjust the 15
mu2TimesThickness2 = log(image1+1) - log(image2+1);
```

or something like that. Don't you agree with my math?

mona on 27 Feb 2013

Yes, I do agree with you on this context. Although I don't understand what you assumed related to "background correct" but here's a simple case scenario of what I intend.

I just need the vessel to be darkened enough so that it is the most prominent feature of the image and for that purpose, the patches in the background should be suppressed as much as possible. Therefore, in a very simple coding,

```I =double(rgb2gray(my image));
se = strel('disk',500);
g2 = imclose(I,se);
g2=mat2gray(g2);
I2 = I - g2;
figure(), imshow(I2,[])
```

which ofcourse doesn't work but atleast portrays the idea.

Image Analyst on 27 Feb 2013

You didn't do what I said. Try this:

```grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
if numberOfColorBands > 1
grayImage = rgb2gray(grayImage);
end
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')
```
```% Close the image
se = strel('disk', 21);
closedImage = imclose(grayImage, se);
subplot(2, 2, 2);
imshow(closedImage, []);
title('Closed Image', 'FontSize', fontSize);
```
```% Subtract to get the vessels alone.
vesselImage = log(1+double(closedImage)) - log(1+double(grayImage));
subplot(2, 2, 3);
imshow(vesselImage, []);
title('Subtracted Image', 'FontSize', fontSize);
```

I think the output looks pretty good. If you don't want the vessels to be white (which is normal for "foreground" objects, especially if you want to use regionprops()), then you can just reverse the subtraction:

```vesselImage = log(1+double(grayImage)) - log(1+double(closedImage));
```