[maemo-developers] raw image buffer and gstv4l2camsrc

[From: Marco Ballesio]

Hi Nicolai,

have you tried using the camerabin element? It provides much more
facilities (e.g. AWB) than v4lcamsrc (and it ultimately uses the
latter as a source). Btw, some comments below..

On 3/9/11, Nicolai Hess <nicolaihess at web.de> wrote:
> Hi,
> I hope someone can help me or points me to someone else how knows
> something about the gstv4l2camsrc.
>
> I have got a question regarding raw-image buffers in gstv4l2camsrc.c
> (in gstreamer0.10-plugins-camera-
> 0.79 for Fremantle).
>
> I am interested in this method:
> gst_v4l2camsrc_send_raw_frame (GstV4l2CamSrc *v4l2camsrc, GstBuffer *buf).
> I know the method can copy the raw-image buffer end send this over the
> GstBus.
> This would be a good way to make raw-images with the N900 camera.
>

A simpler way is to just use the buffer pushed through the pipeline.
It's possible, for instance, to write exactly one frame to a file by
connecting the v4l2camsrc to a filesink. Maybe I can give you more
hints if you explain what you're exactly trying to do.

> But sadly not the full image data is copied. Here are my observations:
>
> The cameradriver somewhere decides(I couldn't find out where or how) the
> biggest
> image resolution would be 2576x1960 pixels with 2 bytes per pixel, so the
> image data would
> be  10097920 bytes.

probably you've not set the caps (e.g. resolution, frame rate, color
space, etc.) on the v4l2camsrc sink pad.

Regards

> In the method:
> gst_v4l2camsrc_send_raw_frame (GstV4l2CamSrc *v4l2camsrc, GstBuffer *buf)
> are two GstBuffer,
> the argument of this method "buf" which holds the image data from the camera
> driver
> and the new copy of this buffer "raw_buffer".
>
> buf buffer is copied with:
>   raw_buffer = gst_buffer_copy (buf);
>
> The amount of bytes copied are based on the size of the source buffer
> (10097920 bytes).
> Now the raw_buffer size attribute is changed based on the raw_caps from the
> camera driver:
>   /* calculate raw_size from raw_caps */
>   raw_s = gst_caps_get_structure (raw_caps, 0);
>   gst_structure_get_int (raw_s, "width", &raw_width);
>   gst_structure_get_int (raw_s, "height", &raw_height);
>   raw_size = raw_width * raw_height * 2;
>
> But the raw_buffer size isn't 10097920, the actual size is computed based
> on the bayer-raw BA10 format with a 2952x1968 resolution with 2 bytes per
> pixel.
>
> That means the buffer copy send over GstBus has the size 10202112, but the
> last
> 104192 are mostly garbage because the call
>   raw_buffer = gst_buffer_copy (buf);
> only wrote bytes of "buf" data (10097920).
>
> Of course, I could change my application to store only a raw-image of
> 2576x1960.
> But what bothers me is, the source buffer (buf) actually has the full
> 2592x1968x2 data!
> I made a quick and dirty change to the above mentioned method to write out
> the
> full buffer, and it indeed contains valid image data.
>
> So, my questions are, is it a bug, that the source buffer thinks its size is
> 10097920,
> whereas it actually holds 10202112 bytes of image data?
> And where is this 2576x1960 resolution setting? When I request the supported
> resolutions (v4l2camsrc->formats) I don't get 2576x1960 but 2592x1968
> instead.
>
> regards
> Nicolai
>