[FFmpeg-devel] [PATCH] Add a gamma flag to exr loader to avoid banding

[Michael Niedermayer]

On Sun, Apr 27, 2014 at 06:04:33PM +0200, Michael Niedermayer wrote:
> On Sun, Apr 27, 2014 at 10:43:09AM -0300, Gonzalo Garramuno wrote:
> > Attached is a patch to add a gamma flag to the exr loader.  This is
> > needed to avoid banding artifacts when gammaing the picture.
> > Currently, if done with a video filter, the process is done on uints
> > instead of full float.
> 
> >  Changelog        |    1 
> >  libavcodec/exr.c |  138 ++++++++++++++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 117 insertions(+), 22 deletions(-)
> > 828c54dedd21b004de00e049b4fa4b2f72ae78b1  exr_gamma.patch
> > diff --git a/Changelog b/Changelog
> > index daaa1ea..a726823 100644
> > --- a/Changelog
> > +++ b/Changelog
> > @@ -2,6 +2,7 @@ Entries are sorted chronologically from oldest to youngest within each release,
> >  releases are sorted from youngest to oldest.
> >  
> >  version <next>:
> > +- EXR loader supports a gamma flag
> >  - AC3 fixed-point decoding
> >  - shuffleplanes filter
> >  - subfile protocol
> > diff --git a/libavcodec/exr.c b/libavcodec/exr.c
> > index 084025a..8c2425c 100644
> > --- a/libavcodec/exr.c
> > +++ b/libavcodec/exr.c
> > @@ -31,6 +31,7 @@
> >   */
> >  
> >  #include <zlib.h>
> > +#include <float.h>
> >  
> >  #include "libavutil/imgutils.h"
> >  #include "libavutil/opt.h"
> > @@ -106,8 +107,30 @@ typedef struct EXRContext {
> >      EXRThreadData *thread_data;
> >  
> >      const char *layer;
> > +
> > +    float gamma;
> > +
> >  } EXRContext;
> >  
> 
> > +union FP32 {
> > +    uint32_t u;
> > +    float f;
> > +    struct {
> > +        unsigned int Mantissa : 23;
> > +        unsigned int Exponent : 8;
> > +        unsigned int Sign : 1;
> > +    };
> > +} FP32;
> > +
> > +union FP16 {
> > +    uint16_t u;
> > +    struct {
> > +        unsigned int Mantissa : 10;
> > +        unsigned int Exponent : 5;
> > +        unsigned int Sign : 1;
> > +     };
> > +} FP16;
> 
> that way to access parts of a float is not portable
> 
> see libavutil/intfloat.h

or for 16bit floats you could simply use a LUT


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator
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