what threshold values should be set to detect edges in a fire image?i have normalized the values to the range [0 1].Please help me in setting appropriate low and high threshold..

I am working on fire and flame images...i have found the gradient of the images after normalizing their grayscale values.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

[Image Analyst]

Haven't seen your image yet, but I bet a DoG Filter would work better than a gradient.

[Walter Roberson]

It is not clear to me that fire has well-defined edges, or that the edges would be in the visible spectrum.

[Image Analyst]

I'm sure it will be a continuum. We'll see once the image is posted. You'll probably just have to make some arbitrary judgment call as to what an edge is.