Threshold in image processing

Hi guys.

I am beginner in image processing. I want to determine value of T. I have tried used global threshold for my image. However, the image become white. I read some article said sometimes global threshold are not suitable for image. So, i assume my image is not suitable for global threshold. So, anyone knows how to determine the value of T for this picture?

Answer 1

[Image Analyst]

What kind of thresholding algorithm you use really depends on the image and what you want to find in the image. Often, like in your case, you'll need to do some preprocessing before you can get to an image that can be thresholded. For example you would need to do color segmentation to pick out the color you want. Part of color segmentation involves thresholding. See my File Exchange for some color segmentation demos. http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

[Maximum]

Thank you for your reply. Do you mean that my image is not suitable using graythresh which is Global image threshold using Otsu's method?

[Image Analyst]

No, it's not. Otsu is meant for gray scale images, not color ones, though you can do it on each color channel independently if you want. It may or may not segment out the exact color of blue that you're interested in - you just have to try it and see. If it doesn't then you'll have to derive your own algorithm. Otsu is best for high contract objects on a uniform background - images that have a histogram comprised of two well separated humps.