Re: [RFC/PATCH 3/5] v4l: Add V4L2_CID_METERING_MODE camera control

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hi Laurent,

thanks for the comments.

On 12/06/2011 01:32 PM, Laurent Pinchart wrote:
> On Sunday 04 December 2011 16:16:14 Sylwester Nawrocki wrote:
>> The V4L2_CID_METERING_MODE control allows to determine what method
>> is used by the camera to measure the amount of light available for
>> automatic exposure control.
>>
>> Signed-off-by: Sylwester Nawrocki <snjw23@gmail.com>
>> ---
>>  Documentation/DocBook/media/v4l/controls.xml |   31
>> ++++++++++++++++++++++++++ drivers/media/video/v4l2-ctrls.c             | 
>>   2 +
>>  include/linux/videodev2.h                    |    7 ++++++
>>  3 files changed, 40 insertions(+), 0 deletions(-)
>>
>> diff --git a/Documentation/DocBook/media/v4l/controls.xml
>> b/Documentation/DocBook/media/v4l/controls.xml index 5ccb0b0..53d7c08
>> 100644
>> --- a/Documentation/DocBook/media/v4l/controls.xml
>> +++ b/Documentation/DocBook/media/v4l/controls.xml
>> @@ -2893,6 +2893,7 @@ mechanical obturation of the sensor and firmware
>> image processing, but the device is not restricted to these methods.
>> Devices that implement the privacy control must support read access and
>> may support write access.</entry> </row>
>> +	  <row><entry></entry></row>
>>
>>  	  <row>
>>  	    <entry
>> spanname="id"><constant>V4L2_CID_BAND_STOP_FILTER</constant>&nbsp;</entry>
>> @@ -2902,6 +2903,36 @@ camera sensor on or off, or specify its strength.
>> Such band-stop filters can be used, for example, to filter out the
>> fluorescent light component.</entry> </row>
>>  	  <row><entry></entry></row>
>> +
>> +	  <row id="v4l2-metering-mode">
>> +	    <entry
>> spanname="id"><constant>V4L2_CID_METERING_MODE</constant>&nbsp;</entry> +	
>>    <entry>enum&nbsp;v4l2_metering_mode</entry>
>> +	  </row><row><entry spanname="descr">Determines how the camera measures
>> +the amount of light available to expose a frame. Possible values
>> are:</entry> +	  </row>
>> +	  <row>
>> +	    <entrytbl spanname="descr" cols="2">
>> +	      <tbody valign="top">
>> +		<row>
>> +		  <entry><constant>V4L2_METERING_MODE_AVERAGE</constant>&nbsp;</entry>
>> +		  <entry>Use the light information coming from the entire scene
>> +and average giving no weighting to any particular portion of the metered
>> area. +		  </entry>
>> +		</row>
>> +		<row>
>> +		 
>> <entry><constant>V4L2_METERING_MODE_CENTER_WEIGHTED</constant>&nbsp;</entr
>> y> +		  <entry>Average the light information coming from the entire scene
>> +giving priority to the center of the metered area.</entry>
>> +		</row>
>> +		<row>
>> +		  <entry><constant>V4L2_METERING_MODE_SPOT</constant>&nbsp;</entry>
>> +		  <entry>Measure only very small area at the cent-re of the
>> scene.</entry> +		</row>
>> +	      </tbody>
> 
> For the last two cases, would it also make sense to specify the center of the 
> weighted area and the spot location ?

Yes, that's quite basic requirement as well.. A means to determine the 
location would be also needed for some auto focus algorithms.
 
Additionally for V4L2_METERING_MODE_CENTER_WEIGHTED it's also needed to
specify the size of the area (width/height).

What do you think about defining new control for passing pixel position,
i.e. modifying struct v4l2_ext_control to something like:

struct v4l2_ext_control {
	__u32 id;
	__u32 size;
	__u32 reserved2[1];
	union {
		__s32 value;
		__s64 value64;
		struct v4l2_point position;
		char *string;
	};
} __attribute__ ((packed));

where:

struct v4l2_point {
	__s32 x;
	__s32 y;
};


or should we rather use ioctls for things like that ?


-- 
Regards,
Sylwester