Re: Zooming with V4L2

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Shuzhen,

On Saturday 20 November 2010 00:17:23 Shuzhen Wang wrote:
> Hello,
> 
> I am working on a SOC V4L2 driver, and need to implement zoom
> functionality.
> 
> From application, there are 2 ways to do zooming. The 1st way is to use
> cropping and scaling as described in section 1.11.1. The application needs
> to figure out what the steps will be, and calling VIDIOC_S_CROP.
> 
> The 2nd way is to use V4L2_CID_ZOOM_ABSOLUTE and V4L2_CID_ZOOM_RELATIVE as
> described by Laurent in
> http://video4linux-list.1448896.n2.nabble.com/RFC-Zoom-controls-in-V4L2-
td1451987.html.
> 
> Our camera hardware supports digital zoom. However, it acts LIKE optical
> zoom because it doesn't do upscaling, so no video quality is sacrificed.

How can you apply a digital zoom, keeping the output size constant, without 
performing upscaling ?

> As a driver writter, is it okay to support only V4L2_CID_ZOOM_ABSOLUTE and
> V4L2_CID_ZOOM_RELATIVE?
> 
> I guess it also depends on how zooming is done for most of the V4L2 user
> application out there.

The V4L2_CID_ZOOM_* controls are really meant for optical zoom. Digital zoom 
should be implemented using cropping.

-- 
Regards,

Laurent Pinchart