Is this a framebuffer job?

edgar edgar-rft at
Thu Nov 7 11:35:17 PST 2013

Am Thu, 7 Nov 2013 13:26:14 -0500
schrieb Gene Heskett <gheskett at>:

> 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 instance.
> 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

This is a job for a camera with a telephoto lens.
You're using a camera with a wrong lens, that's all.

For many cameras there are telephoto adaptors available.

Capturing 2540x19xx pixels for a 240x240 picture is an
extremely unreasonable approach.

(I already sent this message some time ago, but it didn't
appear on the list, please excuse if it's double now.)

- edgar

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