can anyone help?
i'm using the standard example of capture.c; i replaced the process_image
function, but i can't figure out the format for this buffer. i've gone
through the docs again
my code below assumes it's just greyscale values, single-pixel-255. do you
know what the format is?
On 10/5/07, Geoffrey Plitt <[EMAIL PROTECTED]> wrote:
>
> 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<http://v4l2spec.bytesex.org/v4l2spec/capture.c>
> >
> >
> >
> >
>
>
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