From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id mAJ9NQwQ027887 for ; Wed, 19 Nov 2008 04:23:26 -0500 Received: from smtp4.versatel.nl (smtp4.versatel.nl [62.58.50.91]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id mAJ9NDVF006259 for ; Wed, 19 Nov 2008 04:23:14 -0500 Message-ID: <4923DC47.6010101@hhs.nl> Date: Wed, 19 Nov 2008 10:28:39 +0100 From: Hans de Goede MIME-Version: 1.0 To: Linux and Kernel Video Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: =?windows-1252?Q?Luk=E1=9A_Karas?= Subject: RFC: API to query webcams for various webcam specific properties List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: video4linux-list-bounces@redhat.com Errors-To: video4linux-list-bounces@redhat.com List-ID: Hi All, With libv4l giving us the ability to do some much needed image conversion in userspace, it has become clear that for (some) webcams more processing then just format conversion is necessary. So far I've been keeping various proposed patches for doing things like software white balance correction out of libv4l as I first want a proper API for drivers to signal they need this to libv4l. Part of the problem is that various cams needs various additional processing steps for best results, and currently there is no way to ask a driver which additional steps should be done (and using which values). Another part is that we do not have a complete picture of all possible existing processing steps we want to do, so what ever we come up with needs to be extensible. To give an idea, here are a few things which libv4l should know about an video input source: -does this cam need software whitebalance -does this cam need software auto exposure -does this cam need gamma correction, and what initial gamma to use -if the sensor is mounted upside down, and the hardware cannot flip the image itself This has been discussed at the plumbers conference, and there the solution we came up with for "does this cam need software whitebalance?" was (AFAIK), check if has a V4L2_CID_AUTO_WHITE_BALANCE, if it does not do software whitebalance. This of course means we will be doing software whitebalance on things like framefrabbers etc. too, so the plan was to combine this with an "is_webcam" flag in the capabilities struct. The is_webcam workaround, already shows what is wrong with this approach, we are checking for something not being there, were we should be checking for the driver asking something actively, So we need an extensible mechanism to query devices if they could benefit from certain additional processing being done on the generated image data. This sounds a lot like the existing mechanism for v4l2 controls, except that these are all read only controls, and not controls which we want to show up in v4l control panels like v4l2ucp. Still I think that using the existing controls mechanism is the best way todo this, so therefor I propose to add a number of standard CID's to query the things listed above. All these CID's will always be shown by the driver as readonly and disabled (as they are not really controls). Here is an initial proposal for the new CID's, I'm sure the list will grow this is just a first revision: #define V4L2_CTRL_CLASS_CAMERA_PROPERTY 0x009b0000 #define V4L2_CID_CAMERA_PROPERTY_CLASS_BASE \ (V4L2_CTRL_CLASS_CAMERA_PROPERTY | 0x900) #define V4L2_CID_CAMERA_PROPERTY_CLASS \ (V4L2_CTRL_CLASS_CAMERA_PROPERTY | 1) /* Booleans */ #define V4L2_CID_WANTS_SW_WHITEBALANCE (V4L2_CID_CAMERA_PROPERTY_CLASS_BASE+1) #define V4L2_CID_WANTS_SW_AUTO_EXPOSURE (V4L2_CID_CAMERA_PROPERTY_CLASS_BASE+2) #define V4L2_CID_WANTS_SW_GAMMA_CORRECT (V4L2_CID_CAMERA_PROPERTY_CLASS_BASE+3) #define V4L2_CID_SENSOR_UPSIDE_DOWN (V4L2_CID_CAMERA_PROPERTY_CLASS_BASE+4) /* Fixed point, 16.16 stored in 32 bit integer */ #define V4L2_CID_DEF_GAMMA_CORR_FACTOR (V4L2_CID_CAMERA_PROPERTY_CLASS_BASE+5) Please let me know what you think of this proposal, as I would like to move forward with this soon. Regards, Hans -- video4linux-list mailing list Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe https://www.redhat.com/mailman/listinfo/video4linux-list