Nate,
Thanks again for your help. I've got some progress. I modified the
process_image function to write out a PGM file:
static void
process_image (const void * p)
{
FILE *out = fopen(" out.pgm", "w");
fprintf(out,"P2\n");
fprintf(out,"#CREATOR: ggp\n");
fprintf(out,"640 480\n");
fprintf(out,"255\n");
int x;
int y;
unsigned char * pixel = p+1;
for(x=0; x<WIDTH; x++)
{
for(y=0; y<HEIGHT; y++)
{
fprintf(out,"%u ",*pixel);
pixel++;
}
fprintf(out,"\n");
}
fclose(out);
exit(0);
}
but I don't think I understand the contents of the buf completely. Attached
is the resulting image - I can see the flourescent light in there, but there
are error patterns all over.
Any ideas?
-Geoff
On 10/5/07, Nathanael Galpin <[EMAIL PROTECTED]> wrote:
>
> Hey Geoff,
>
>
>
> This is a great file to start with. In fact it's what I used first. Couple
> things make it a bit tricky. One is that he's using switch statements to
> separate different ways to read from the cameras, so you'll want to note
> which method you're using, (should be MMAP).
>
>
>
> The line where he actually captures a frame is in the read_frame function.
>
>
>
>
> (-1 == xioctl (fd, VIDIOC_DQBUF, &buf))
>
>
>
> This blocks until it's able to deque a frame from the camera (unless you
> specify non-blocking when you open the cam file, in which case it returns -1
> when it can't immediately deque a frame). You can get at the raw frame data
> through the buf struct.
>
>
>
> A little farther down, he re-enques the buffer after he's finished with
> with this line:
>
>
>
> (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
>
>
>
> You can read through the V4L2 spec a bit at bytesex.org to check out the
> parameters of the buf struct.
>
>
>
> If you want to display this data, a quick way to do it would be to pull
> the Y values from the buffer and use these to write a grayscale image to the
> screen. I used a Qt picture object when I first started doing this, and that
> actually worked quite well.
>
>
>
> Hope that helps, and good luck!
>
>
>
>
>
> -- Nathanael
>
>
> ------------------------------
>
> *From:* [EMAIL PROTECTED] [mailto:
> [EMAIL PROTECTED] <[EMAIL PROTECTED]>
> .berlios.de <[EMAIL PROTECTED]>] *On Behalf Of *Geoffrey
> Plitt
> *Sent:* Thursday, October 04, 2007 9:18 PM
>
> hey christopher. this file looks promising, but it doesn't do anything
> with the frames. i compiled/ran and it just prints dots, you have to take as
> faith that it's capturing - it doesn't output or save the frames. in fact, i
> can't tell exactly where in the code it actually grabs a frame and has
> access to the frame's pixel buffer. any clues?
> -geoff
>
> On 10/4/07, *Christopher HORLER* <[EMAIL PROTECTED]> wrote:
>
> http://v4l2spec.bytesex.org/v4l2spec/capture.c
>
>
>
>
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