[Libav-user] change pixel format without scaling data ? // more 2

[jim morgenstern]

Well, that is my problem - it is not clear how it scales or why if I don't
request it!!  What we used to call an 'undocumented feature'

 

The input to the context is the input format, the input sizes, the output
format and the output sizes.  Gray levels, scaling, expected means etc.
have no part of the context or the input.  I would post my  code but I am
away from the workstation at the moment.  But if you look at the function
calls for sws_getcontext and  sws_scale you will no mention of modifying
gray levels.

 

Thanks guys

 

Jim

 

From: libav-user-bounces at ffmpeg.org [mailto:libav-user-bounces at ffmpeg.org]
On Behalf Of Roman Ryltsov
Sent: Saturday, January 05, 2013 11:00 AM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice
and libavfilter.
Subject: Re: [Libav-user] change pixel format without scaling data ? // more
1

 

It is not quite clear how it scales if you don't request it. Perhaps you
could post some code, esp. your SWS context initialization arguments?

Roman

On Sat, Jan 5, 2013 at 5:55 PM, jim morgenstern <jmorgie at yahoo.com> wrote:

I have 10 bit data;  I am converting from say YUV422 to YUV444 or RGB etc.;
swscale is useful for changing the pixel format.  But I find that my 10bit
data is getting scaled to 16 bit such that when I output only 10bits I have,
well, wrap around etc.  I am not asking ffmpeg to rescale the data
automatically, I want the scale left alone.

So a) is there a better way to change pixel format?  B) a way to turn off
gray-level scaling ??

-----Original Message-----
From: libav-user-bounces at ffmpeg.org [mailto:libav-user-bounces at ffmpeg.org]
On Behalf Of Carl Eugen Hoyos
Sent: Saturday, January 05, 2013 10:27 AM
To: libav-user at ffmpeg.org
Subject: Re: [Libav-user] change pixel format without scaling data ?

jim morgenstern <jmorgie at ...> writes:

> I am using sws_scale to change the pixel formatting but this routine
> is also changing the scale of the data graylevel values themselves and
> I do not want it to.

I am not sure I understand:
Are you converting from GRAY8 to GRAY8A without changing the resolution but
the values are changed?

Generally, swscale should be used both if you want to change a frame's
resolution and if you only want to change the pix_fmt.

Carl Eugen

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