how to calculate threshold value in frame difference algorithm

i was studying frame difference algorithms and in every pdf it says find threshold value and didn't mention how can anyone tell me how

[Ben11]

what kind of algorithms? I think the choice of threshold is arbitrary, depending on what you want to get. Can you give examples?

[Ayesha ayub]

for motion detection i am using frame difference algorithm that is current frame-previous frame but this algorithm is comparing the frame difference with a threshold value. i saw a code where they took threshold 25 with no reason why

[Image Analyst]

Because it worked for them. The value that "works" for you may be different, as I said in my Answer below.

Answer 1

[Image Analyst]

Subtract the frames. Be sure to cast to double before you do so to avoid clipping values less than zero. You might want to take the absolute value of the difference image. Then pick a threshold however you want. The lower the threshold, the more stuff you will get and the higher the threshold the fewer pixels will be selected. Choose the threshold to get just the pixels you want and no others. Thresholding may not do it - you may have to combine with other methods, like spatial operations that consider neighborhoods around each pixel, or shape, or whatever. It really depends on what you want to find.

[Ayesha ayub]

thank you it helped a lot

[Image Analyst]

Can you go ahead and officially "Accept" the answer then? Thanks in advance.

[Mohammedashraf Shaikh]

By frame differncing, I got the subtracted image, now how to get thresold and use thresold to detect activity