Is this a framebuffer job?

Gene Heskett gheskett at
Thu Nov 7 10:26:14 PST 2013

Hello all;

I, and several others are attempting to make use of camera vision in a 
machine shop environment, to auto position a lathe or milling machine for 

My current camera is the highest priced of the logitech webcams, with a 
nominally 5 megapixel format.

But for our purposes, the field of view at 2540x19xx is at least 75 
degrees.  We need maybe 5 degrees because all we are interested in is the 
pixel under the center pixel of the crosshairs.  This, when inspecting the 
workpiece from 50mm, should represent accuracy's in the thousandth of an 
inch category, and would generally be quite useful to us.

So, is it possible to setup a framebuffer with 2 circular pointers, the 
input pointer writing the 5 megapixel image as it comes in, and an output 
pointer that only reads out the central 100x100 pixels of the image, maybe 
even 240x240 but for our uses its overkill.

The problem as it exists now is the processing time for the video image to 
get thru camview-emc and actually be presented on our computer screens, is 
on the order of 3 to 5 seconds when the whole signal chain has to deal with 
the 2540x19xx format of a decent webcam.  If we could throw away all but 
the mathematical central area of the image that the rest of the video chain 
had to process using only 1 core of a 1.4Ghz atom processor, it seems we 
could save many valuable seconds of image processing time.

The V4L list didn't understand what I wanted, so everything they suggested 
threw away resolution which we don't want to do, and gave the same field of 
view in the output, but converted to useless fuzz.  Hence I come here in 
search of help.  Effectively, we need extreme telephoto at maybe 57,600 
pixels (240x240 for this example) resolution, captured pixel by pixel from 
the central 57,600 pixels of the input for this application.

Thank you for any usable suggestions.

Cheers, Gene
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