Re: [soc-camera] about the y_skip_top parameter

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: video4linux-list@redhat.com
Subject: Re: [soc-camera] about the y_skip_top parameter
Date: Tue, 9 Sep 2008 09:19:14 +0200	[thread overview]
Message-ID: <20080909071914.GC7126@pengutronix.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0809081248360.4466@axis700.grange>

On Tue, Sep 09, 2008 at 08:38:55AM +0200, Guennadi Liakhovetski wrote:
> On Mon, 8 Sep 2008, Sascha Hauer wrote:
> 
> > On Fri, Sep 05, 2008 at 08:12:56PM +0200, Guennadi Liakhovetski wrote:
> > > 
> > > Hm, AFAIR, the reason was different. I was told, that "all" cameras 
> > > corrupt the first line, that's why that parameter has been introduced. I 
> > > don't think it was related to PXA270. In any case, why don't you just set 
> > > this parameter to whatever you need in your hist driver .add method, for 
> > > example, before calling camera's .init?
> > 
> > That's what I'm doing at the moment. I just had the feeling that there
> > is a bug fixed in the wrong place, but I did not know that it's the cameras
> > that corrupt the first line.
> > Anyway, what in case of bayer cameras? don't we have to skip the first
> > two lines then?
> 
> I think so, yes. Or you start with the wrong line in your user-space 
> application.
> 
> > I'm asking because I'm still struggling with getting the
> > correct pixel in the top left corner without introducing funny offsets.
> > This brings me back to the question: Which color does the top left
> > corner have? http://v4l2spec.bytesex.org/spec/r3735.htm says the first is a
> > blue/red line, due to y_skip_top=1 the pxa actually delivers a green/red
> > line
> 
> http://www.siliconimaging.com/RGB%20Bayer.htm shows a green/red line on 
> the top. But look in your camera datasheet - at least datasheets I was 
> working with did describe the specific pattern the camera was producing. 
> For example, mt9m001 also specifies green/red at the top.

Ah ok, so even the Micron chips are not consistent. I wonder whether we
should move the pictures in kernel so that they all have the same pixel
in the top left corner or introduce a second bayer fourcc then. It
doesn't seem practical that the userspace apps hold a database of camera
chips.

Sascha

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