MATLAB: How to make the edge darker (increase contrast?)

contrast imadjust

I want to somehow increase the contrast if it is the thing to do. What I want is make the edge darker and clearer, so that I can detect it better in binary image. For example this is what I want:

But I made this through picture manager not MATLAB. How can I do this with matlab? If I use imadjust or etc for enhancing contrast, I get this:

which is not what I want. Now these are my questions:

1. How can I use MATLAB to get the second image? I do not know how to use imajust or imcontrast to do so.

2. Is my whole method good or efficient for my final purpose? (clearer edge in binary)?

Thanks so much Steven

Best Answer

Increasing contrast with a point process like imadjust is not what you want to do. Just think about it - it won't change the shape of your edge, it will just make the threshold occur at a different value. You would need to do a spatial filter, something like mean shift or something like that. But to tell the truth I'm not sure you need to make the edge darker. What are you trying to measure exactly and then I can recommend an approach?

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MATLAB: Filling regions in binary image

After your closing, you should use imfill(). It may never be pretty but since the hand (that's what it looks like to me) is never going to be exactly the same shape anyway, your algorithm must be robust enough to handle slight perturbations in the outline/perimeter. If it can't handle that then it's never going to do what you want (gesture analysis or whatever).

MATLAB: How to calculate Black area

No, that's not right. It's as I told you at first.

When you do

binaryImage = grayImage < 128; % Find dark pixels.  Dark = true, 1, white.

you're creating a matrix that is "true" wherever the image is dark . If you sum that, it treats the "true" pixels as 1, and thus, counts them - counts the dark pixels. So you're getting the sum of the "true/1/white" pixels in the binary image which means your getting the count of the dark pixels of the gray scale image. Doing it your complicated way would count the bright pixels. By the way, if you wanted the binary image to be false where the gray scale image was dark, you'd flip the less than sign and then sum the inverse, which is much simpler than doing the multi-step process you did.

binaryImage = grayImage > 128; % Find bright pixels instead of dark pixels.
numDarkPixels = sum(~binaryImage(:)); % Notice I had to invert the image with~.

Best Answer

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