Make matrix numbers below 'X' equal to zero and help with overlaying images

Hey guys

I am doing some image processing from HD video. I am reading the video in frame by frame, converting each frame to grey and then subtracting a template image from them.

What I am doing then is overlaying the resulting images. Or trying to anyway.

The first thing I need help with, is that really I am only interested in a certain event within the images. The event is an electrical discharge and this event shows up as pure white (255). So I want to perform a matrix operation on each image whereby I cull all the numbers less than say 250 and make them zero (but still keeping the original matrix dimensions).

The second thing is, how do I overlay the images ontop of each other so as to build up a plot showing all the locations of this event at once? (ie so I can check that the event occured evenly across an area). is imadd(X,Y) sufficient?

Thanks for any help offered

Alex

Answer 1

[Walter Roberson]

IMG(IMG<250) = 0;

[Walter Roberson]

If the events can overlap, then imadd() may not be suitable.

[Alex Mason]

Wow simple as that? this is my first day really using matlab and I quite like it. Im used to VB, but this is even easier!

yeah the events can overlap, but as they pretty much max out the white value first time, then I dont know what to do. Perhaps giving each image its own false colour?

[Jason]

On a related subject, if IMG is an image (12 bit gray scale), how could you show the image as its normal 12 bit scale, but colour in red all values below a certain value (i.e. IMG<250)?

[Alex Mason]

I cannot get that to work

I assume by IMG you mean whatever variable I have called my image. In this case FF

but FF = FF(FF<250) = 0 is invalid

even FF2 = FF(FF<250) = 0 doesnt work. What am I missing?

[Alex Mason]

oh i dont need the FF= bit, sorted!