[V4L2] EV control API for digital camera

[V4L2] EV control API for digital camera

[DongSoo Kim]

Hello.

When we take pictures, sometimes we don't get satisfied with the
exposure of picture. Too dark or too bright.

For that reason, we need to bias EV which represents Exposure Value.

So..if I want to control digital camera module with V4L2 API, which
API should I take for EV control?

V4L2 document says that V4L2_CID_BRIGHTNESS is for picture brightness,
but it is for "Image properties" and that "image" means the image
frame of TV or PVR things.Am I right?

If I may, can I use V4L2_CID_BRIGHTNESS for EV control of digital cameras?

or..otherwise I should make a new API for that functionality.

I'm little bit confused, because I think the brightness of picture
could differ from exposure value of digital camera..help me ;(


Regards.
Nate




-- 
========================================================
Dong Soo, Kim
Engineer
Mobile S/W Platform Lab. S/W centre
Telecommunication R&D Centre
Samsung Electronics CO., LTD.
e-mail : dongsoo.kim@gmail.com
           dongsoo45.kim@samsung.com
========================================================

Re: [V4L2] EV control API for digital camera

[Guennadi Liakhovetski]

[removed redhat list from CC]

On Thu, 29 Jan 2009, DongSoo Kim wrote:

> Hello.
> 
> When we take pictures, sometimes we don't get satisfied with the
> exposure of picture. Too dark or too bright.
> 
> For that reason, we need to bias EV which represents Exposure Value.
> 
> So..if I want to control digital camera module with V4L2 API, which
> API should I take for EV control?
> 
> V4L2 document says that V4L2_CID_BRIGHTNESS is for picture brightness,
> but it is for "Image properties" and that "image" means the image
> frame of TV or PVR things.Am I right?

There's also V4L2_CID_EXPOSURE

> 
> If I may, can I use V4L2_CID_BRIGHTNESS for EV control of digital cameras?
> 
> or..otherwise I should make a new API for that functionality.
> 
> I'm little bit confused, because I think the brightness of picture
> could differ from exposure value of digital camera..help me ;(

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer

Re: [V4L2] EV control API for digital camera

[Dongsoo Kim]

Thank you.

So if V4L2_CID_EXPOSURE is for Exposure Value control, I think there  
is no api for exposure metering. right?

Actually many of APIs for camera are missing I guess.

Cheers
Nate


2009. 01. 30, 오전 3:35, Guennadi Liakhovetski 작성:

> [removed redhat list from CC]
>
> On Thu, 29 Jan 2009, DongSoo Kim wrote:
>
>> Hello.
>>
>> When we take pictures, sometimes we don't get satisfied with the
>> exposure of picture. Too dark or too bright.
>>
>> For that reason, we need to bias EV which represents Exposure Value.
>>
>> So..if I want to control digital camera module with V4L2 API, which
>> API should I take for EV control?
>>
>> V4L2 document says that V4L2_CID_BRIGHTNESS is for picture  
>> brightness,
>> but it is for "Image properties" and that "image" means the image
>> frame of TV or PVR things.Am I right?
>
> There's also V4L2_CID_EXPOSURE
>
>>
>> If I may, can I use V4L2_CID_BRIGHTNESS for EV control of digital  
>> cameras?
>>
>> or..otherwise I should make a new API for that functionality.
>>
>> I'm little bit confused, because I think the brightness of picture
>> could differ from exposure value of digital camera..help me ;(
>
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer

Re: [V4L2] EV control API for digital camera

[Laurent Pinchart]

Hi Nate,

On Thursday 29 January 2009, Dongsoo Kim wrote:
> Thank you.
>
> So if V4L2_CID_EXPOSURE is for Exposure Value control, I think there
> is no api for exposure metering. right?

V4L2_CID_EXPOSURE controls the exposure time. This is often implemented 
through a mechanical or electronic shutter in the device.

What kind of exposure metering do you have in mind ? Can you give us some 
details ?

> Actually many of APIs for camera are missing I guess.

You're probably right. The V4L1/V4L2 API have been developed for frame 
grabbers and extended to webcams. Now that high-end digital cameras get USB 
connectivity, the V4L2 API should be extended with new controls. Feel free to 
submit proposals for discussion on the linux-media mailing list.

Best regards,

Laurent Pinchart

Re: [V4L2] EV control API for digital camera

[Dongsoo Kim]

On 화, 2009-02-03 at 11:20 +0100, Laurent Pinchart wrote:
> Hi Nate,
> 
> On Thursday 29 January 2009, Dongsoo Kim wrote:
> > Thank you.
> >
> > So if V4L2_CID_EXPOSURE is for Exposure Value control, I think there
> > is no api for exposure metering. right?
> 
> V4L2_CID_EXPOSURE controls the exposure time. This is often implemented 
> through a mechanical or electronic shutter in the device.
> 
> What kind of exposure metering do you have in mind ? Can you give us some 
> details ?

I mean photometry which is all about light meter (or exposure meter).
Like spot metering, center weighted things..

> 
> > Actually many of APIs for camera are missing I guess.
> 
> You're probably right. The V4L1/V4L2 API have been developed for frame 
> grabbers and extended to webcams. Now that high-end digital cameras get USB 
> connectivity, the V4L2 API should be extended with new controls. Feel free to 
> submit proposals for discussion on the linux-media mailing list.
> 
Thank you for you encouraging words.
Actually I'm working on some ISP devices from NEC, Fujitsu. and ARM SOC
camera interface peripheral like PXA3, S3C64XX, OMAP3..
I wish I could make a device very close to a real digital camera.
It wouldn't take so long until I submit a RFC about V4L2 API for digital
camera :) (I hope so at least)
Cheers.

Regards,
Nate