Zooming with V4L2
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Hi Shuzhen,
Quoted 5 lines · 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.
Quoted 7 lines
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_ABSOLUTEandV4L2_CID_ZOOM_RELATIVEas described by Laurent in
http://video4linux-list.1448896.n2.nabble.com/RFC-Zoom-controls-in-V4L2-
td1451987.html.
Quoted 3 lines
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 ?
Quoted 5 lines
As a driver writter, is it okay to support only
V4L2_CID_ZOOM_ABSOLUTEandV4L2_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.
Signature · 3 lines
Regards, Laurent Pinchart
Hello, Laurent,
Thank you for the reply.
In our case, most of the time the sensor outputs bigger image size than the output size, so the ISP hardware does downscaling.
When zooming in, we can do cropping, and less downscaling to achieve the same output size. All these happen under of the hood of ISP driver. That's why I said it was like optical zoom to the application.
So if "digital zoom == cropping and upscaling", then I don't think my case fits in digital zoom category.
Regards,
Shuzhen
-----Original Message-----
From: Laurent Pinchart [mailto:[email protected]]
Sent: Saturday, November 20, 2010 9:37 AM
To: Shuzhen Wang
Cc: [email protected]
Subject: Re: Zooming with V4L2
Hi Shuzhen,
Quoted 5 lines · 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.
Quoted 7 lines
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_ABSOLUTEandV4L2_CID_ZOOM_RELATIVEas described by Laurent in
http://video4linux-list.1448896.n2.nabble.com/RFC-Zoom-controls-in-V4L2-
td1451987.html.
Quoted 3 lines
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 ?
Quoted 5 lines
As a driver writter, is it okay to support only
V4L2_CID_ZOOM_ABSOLUTEandV4L2_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.
Signature · 3 lines
Regards, Laurent Pinchart