From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from perceval.ideasonboard.com ([95.142.166.194]:60499 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753845Ab2IXK77 (ORCPT ); Mon, 24 Sep 2012 06:59:59 -0400 From: Laurent Pinchart To: Hans de Goede Cc: Prabhakar Lad , Hans Verkuil , Sakari Ailus , Guennadi Liakhovetski , Sylwester Nawrocki , dlos , linux-media , Prabhakar Lad , Manjunath Hadli Subject: Re: Gain controls in v4l2-ctrl framework Date: Mon, 24 Sep 2012 13:00:34 +0200 Message-ID: <1440297.PvW0ZMD1YU@avalon> In-Reply-To: <50603C39.9060105@redhat.com> References: <50603C39.9060105@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-media-owner@vger.kernel.org List-ID: Hi Hans, On Monday 24 September 2012 12:55:53 Hans de Goede wrote: > On 09/23/2012 01:26 PM, Prabhakar Lad wrote: > > Hi All, > > > > The CCD/Sensors have the capability to adjust the R/ye, Gr/Cy, Gb/G, > > B/Mg gain values. > > Since these control can be re-usable I am planning to add the > > following gain controls as part of the framework: > > > > 1: V4L2_CID_GAIN_RED > > 2: V4L2_CID_GAIN_GREEN_RED > > 3: V4L2_CID_GAIN_GREEN_BLUE > > Not all sensors have separate V4L2_CID_GAIN_GREEN_RED / > V4L2_CID_GAIN_GREEN_BLUE, so we will need a separate control for sensors > which have one combined gain called simply V4L2_CID_GAIN_GREEN > > Also do we really need separate V4L2_CID_GAIN_GREEN_RED / > V4L2_CID_GAIN_GREEN_BLUE controls? I know hardware has them, but in my > experience that is only done as it is simpler to make the hardware this way > (fully symmetric sensor grid), have you ever tried actually using different > gain settings for the 2 different green rows ? > > I've and that always results in an ugly checker board pattern. So I think we > can and should only have a V4L2_CID_GAIN_GREEN, and for sensors with 2 > green gains have that control both, forcing both to always have the same > setting, which is really what you want anyways ... I've never had to set different gains for the two green components either, although I haven't done much with them. > > 4: V4L2_CID_GAIN_BLUE > > 5: V4L2_CID_GAIN_OFFSET > > GAIN_OFFSET that sounds a bit weird... GAIN_OFFSET sounds like it is > a number which gets added to the 3/4 gain settings before the gain gets > applied, but I assume that you just mean a number which gets added to the > value from the pixel, either before or after the gain is applied and I must > admit I cannot come up with a better name. > > I believe (not sure) that some sensors have these per color ... Some might at least. > The question is if it makes sense to actually control this per color though, > I don't think it does as it is meant to compensate for any fixed measuring > errors, which are the same for all 3/4 colors. The offset is usually applied after the gain, so you might need different offsets to compensate for a fixed error that is multiplied by different gains. > Note that all the sensor cells are exactly the same, later on a color grid > gets added on top of the sensors to turn them into r/g/b cells, but > physically they are the same cells, so with the same process and temperature > caused measuring errors... -- Regards, Laurent Pinchart