Manual thresholding cropping [image processing]

Hi. May i know if manual thresholding allows autocropping? where i set T a value, bw = im2bw(J,T);

because usually auto thresholding was done with autocropping. but i was told me to set a value for my image instead of using graythresh.

Answer 1

[Image Analyst]

Cropping and thresholding are two totally separate and independent operations. One operation does not need, depend on, allow, or enable the other operation at all. I would not say that autothresholding is usually done with autocropping - not in general, though it may be in some specific situation you maybe referring to, like your co-worker's program. You can use graythresh() if you want to determine a threshold value, though in my experience it seldom selects the best threshold. It seems to work best for high contrast situations where foreground and background are well separated in the histogram (i.e., they have vastly different intensities).

[Esther]

does using graythresh meant that it determine the threshold itself? because when I used, bw = im2bw(J,T); manual threshold and proceed to autocropping, it actually threw an error.

[Image Analyst]

graythresh() determines a threshold from the image using the famous Otsu method. It's not a gray level but a normalized gray level in the range 0-1. im2bw() also wants a threshold in the range 0-1. If you have a gray level that's uint8, you have to divide it by 255 to get it into the 0-1 range.

I have no idea what you mean by autocropping. Did you use imcrop() or some other method to do autocropping? What is "auto" about it?

[Esther]

i didn't use imcrop(). but i use method by getting the outmost object border coordinates to crop it out.

[Image Analyst]

You mean like

submatrix = fullMatrix(row1:row2, col1:col2);

? What about this threw an exception?