Luminance gain and offset filtering in virtualdub

[powerful.br]

Hi, im new in this forum, and i am in needing of some help!
What i am searching for is a filter for virtualdub that does luminance gain and offset, analogous to what DVDx and ffdshow (only in playback) do. I tried many filters and none of them did the same way DVDx and ffdshow do.
I used DVDx until today because my videos were from a Sony DSC S60 (mpeg), and the application was perfect for fixing them (it only opens mpeg), but now my videos are MJPEG (avi) from a Canon A710 and i can't convert them to mpeg for fixing in DVDx.

Thanks in advance!

[jagabo]

I think the Levels filter does what you want.

[powerful.br]

Thanks for the reply, but unfortunately the levels filter doesn't do what the luminance filter of DVDx do.

Here I extracted from the DVDx help:

Luminace filter:
Allow to adjust light of source.
The Y plane is the luminance plane (in YUV format)
Apply Gain*Y + Offset on the Y plane.
Gain is 8.8 fixed point value. ( 0 = 0.0 ; 128 = 1.0 ; 256 = 2.0 )
Default is : Not enabled , Gain 128 , Offset 0

I need a filter that does this, gain and offset on the Y plane.
And none of what i tried (many, many...) worked the same way.

[powerful.br]

hum, my mistake.. i was testing with a mpeg from the Sony DSC S60 in virtualdub and the levels filter didn't work (i was trying to force the same results in DVDx and virtualdub with the same file).. but with a MJPEG it works! does anyone know why?

[jagabo]

I never have problems with the levels filter, no matter what the source. What do you mean by "didn't work"? No visible change at all? Couldn't match what you did with DVDx? Couldn't add the filter? COuldn't open your MPEG file?

VirtualDub cannot open MPEG2 files, only MPEG1. If you are working with MPEG2 you need VirtualDubMPEG2 or VirtualDubMod. Or you can use AVISynth to frameserve MPEG2 to VirtualDub.

[powerful.br]

I am working with MPEG-1 in VirtualDub
I couldn't match what i did in DVDx with a MPEG-1 source in virtualdub.. but with a MJPEG source it seems the results are OK (i can't compare with DVDx because it only opens MPEG - but the results appear to be the same as when i play the MJPEG source with ffdshow using picture properties - luminance gain and offset).
But i don't know why there is a difference between sources..

[Soopafresh]

http://compression.ru/video/smart_contrast/index_en.html

[jagabo]

I am working with MPEG-1 in VirtualDub :)
I couldn't match what i did in DVDx with a MPEG-1 source in virtualdub.. but with a MJPEG source it seems the results are OK

I wonder if you have a colorspace issue. I don't know about DVDx, but VirtualDub (all versions) convert video to RGB before applying filters. YV12 data (from the MPEG decoder) will go through a contrast stretch to convert from normal video (as in TV) luminance to RGB brightness. When this happens, everything with a luminance value below 16 in the YUV colorspace becomes black (0,0,0) in RGB. And everything above 235 in YUV becomes white (255,255,255) in RGB.

If the video you are trying to correct is very dark or very bright, you will lose all the details in the very dark or very bright regions. You can get around this with AVISynth or some other program with the option of not stretching the luminance on RGB conversion.

[powerful.br]

First, thanks for the smart contrast filter tip. I've tested it before figuring out my problem and it didn't work too, but now works wonders!

And jagabo, all the videos from the Sony DSC S60 are very dark, so your explanation makes sense. About the AVISynth workaround, i will see this in a near future because i won't work with this camera's videos for a while.
Thanks for the replies