Trouble Removing Uneven Background Lighting from Image

Hello,

As I stated I am having some trouble removing a background from an image. I have tried using imopen, imtophat, and a couple other methods, but all of them result in the same problem. The code considers my entire image as a background. For example, here is my original image.

My code to load it is pretty simple

drop=mat2gray(imread('st000.tif'));

As you can see the illumination is fairly uneven, and when I go to convert it to a bw image it cuts off the last half of the stream. When I try and use imopen to find the background this is what I get.

 background = imopen(drop,strel('disk',15));
 figure()
 imshow(background)

If I use imtophat I get this.

I2 = imtophat(drop,strel('disk',15));
figure()
imshow(I2)

Since this image is a little dark, I tried to enhance it using

I3=imadjust(I2);
figure()
imshow(I3)

which gave me

I can't really use this image, since it is so blurry. I have tried taking a static image with the background, subtracting that from the bw image of the original, and that sort of works.

But as you can see it removed a lot of the resolution on the image, which I think has something to do with how I actually convert it into a bw image. I think I can get a better resolution if I can find a way to make a uniform background before converting it to bw.

Answer 1

[Jeff E]

Try using imbothat instead of imtophat, with a slightly larger kernel size.

I2= imbothat(drop, strel('disk', 30));

worked for me, with the exception of some artifacts around the edge.

[Nathan]

That works fairly well for the most part. however if I try it on a different image that has droplets in it, such as

The droplets are for some reason taken as part of the background. Any tips on this? Should I just change the kernel size until it works?

[Nathan]

Yes. That fixed the problem exactly. And now I can get hi-res bw images. Thank you very much.

[Jeff E]

Use a bigger kernel size. Say, 45 or so. The artifacts around the edges will be bigger, but you'll capture the larger droplets much more effectively.