Re: V4L2_PIX_FMT_RAW
H. Willstrand wrote:
On Thu, Feb 21, 2008 at 7:55 PM, Thomas Kaiser
<linux-dvb@xxxxxxxxxxxxxxx> wrote:
H. Willstrand wrote:
> On Thu, Feb 21, 2008 at 1:00 PM, Thomas Kaiser
> <linux-dvb@xxxxxxxxxxxxxxx> wrote:
>> H. Willstrand wrote:
>> > On Thu, Feb 21, 2008 at 2:20 AM, Daniel Glöckner <daniel-gl@xxxxxxx> wrote:
>> >> On Thu, Feb 21, 2008 at 01:02:39AM +0100, H. Willstrand wrote:
>> >> > What's the problem with having a name of the formalized data in the
>> >> > video stream? ie raw do not mean undefined.
>> >>
>> >> I thought you wanted to avoid having to define V4L2_PIX_FMT_x for an
>> >> exploding number of proprietary formats that are quite similar but still
>> >> incompatible. It makes sense for formats that are used by more than one
>> >> driver.
>> >
>> > Correct, the number of unique pixel formats should be kept down.
>> > Again, comparing with digital cameras there are >200 proprietary
>> > formats and there is a "clean-up" on-going where the "market" is
>> > aiming for a OpenRAW.
>> >
>> > However, by declaring a generic RAW format (which is then driver
>> > specific) doesn't help the user mode app developers. Calling a
>> > multitude of libraries to see if you get lucky might not be a good
>> > idea.
>> >
>> > Still, I'm suspectious about the definition "raw" used here.
>> > RAW should mean unprocessed image data:
>> > * no white balance adjustment
>> > * no color saturation adjustments
>> > * no contrast adjustments
>> > * no sharpness improvements
>> > * no compression with loss
>>
>> Yes, raw means "as it is" no stripping, decoding or removing of SOF headers are
>> done in the driver. May be V4L2_PIX_FMT_AII (AII -> As It Is) is the better name?
>>
>
> I struggle with the probability to find several CCD's having similar
> formats. There aren't so many manifactors of CCD's but they truelly
> can generate divergeting formats. Worst case scenario means >200
> V4L2_PIX_FMT_RAW_...
>
> I think RAW is a OK name, the question is if the subcomponents of the
> RAW formats has similarities, if so they might be standardized.
> Looking into different Sony CCD's it's clearly possible, but after the
> CCD the data has to be buffered, packaged and transmitted which of
> course can be done in several ways...
>
> Cheers,
> Harri
>
>> >
>> > So, by looking for similarities in the "raw" formats where available
>> > there should be a potential to consolidate them.
>> >
>> >>
>> >> > I don't see how separate RAW ioctl's will add value to the V4l2 API,
>> >> > it fits into the current API.
>> >>
>> >> Yes, it does. Each driver having multiple raw formats just needs a
>> >> private control id to select one.
>> >>
>> > I was more thinking about the VIDIOC_S_RAW stuff, a VIDIOC_S_FMT
>> > should do the job.
>> > I.e. I think there should be strong reasons to break V4L2 API behavior.
>> >
>> > Harri
Actually, in a webcam you have the image sensor and a usb bridge. Usually, the
sensor capture a picture in Bayer pattern. This gets forwarded to the usb
bridge. The usb bridge may or may not transfer the picture to an other format
and/or compress it with a standard compression algo or a proprietary compression
algo. The resulting data stream will be transmitted over the usb interface.
Yes, the USB bridge buffers, packages and transmits.
I just would like to get this resulting stream to user space without
manipulation/conversion/decoding of the stream in the kernel module.
That means we don't know what the format is in this data which comes trough the
usb interface. That's way I call it raw.
At the moment with V4L2, I have to forward a stream to user space which is in a
format v4l2 knows. That means I have sometimes to do heavy data processing in
the kernel module to decode/convert the data from the usb stream to a known v4l2
video format.
Drivers should not do any decoding / converting, it's not allowed in
kernel mode.
But you are right, there are a number of V4L1 exceptions:
AR M64278 (arv.c) converts YUV422 to YUV422P
QuickCam (bw-qcam.c) converts RAW to a useful format :)
CPiA (cpia.c) converts 420 to different RGB formats
OmniVision (ov511.c) converts from YUV4:0:0
PWC (V4L2) does decoding
You forgot gspca [1](support of 260 webcams at the moment) and here we even do
jpeg decoding in kernel space to get the proper format for v4l1!
...
However, the Webcams provides only a limited set of formats and the
"raw" are usually available. New drivers with proprietary "raw"
formats should be added to videodev2.h
That means you agree with me?
That's way I want a official way to forward the untouched usb stream to user space!
How the user space application has to react on this stream is an other story, I
think. But there will be some way to tell the usespace application what to do
with this "unknown" stream, I am sure.
Thomas
Cheers,
Harri
Thomas
[1] http://mxhaard.free.fr/download.html
--
http://www.kaiser-linux.li
--
video4linux-list mailing list
Unsubscribe mailto:video4linux-list-request@xxxxxxxxxx?subject=unsubscribe
https://www.redhat.com/mailman/listinfo/video4linux-list