Question

I have a small video clip that I’ve run through my video to image software and noticed that the images come out different. Both set of images are identical in which they are cut at 1 second segments. Where they vary is one of the images seem to be brighter then the other set. I’m trying to think what can cause this subtle difference, but I’m at a loss.

I thought that maybe because the hardware is different that would cause this, but I’m not doing anything on the GPU. I also thought that it could be the codec being used, but if the video is encoded the same way using the same codec and information then would decoding really effect it in this way?

Below is a list of what the program is:

• Takes a video and saves it out as 1 second images
• Uses DirectX in C# to load in a video and saves out the texture.
• Video is encoded using MPEG-4 similar compression

I understand that this may not be much information to go off of, but I am at a loss of where I can look.

Any advice is greatly appreciated.

Answer 1

I’d say that images are not actually different. It is unlikely that MPEG-4 decoding uses any GPU resources. Well, it’s possible to hardware decode MPEG-4 Part 10, but it’s subject to certain conditions too. Far more likely, the effect is due to on of the reasons below (or both):

• if you show the picture up within video streaming context, or as you mentioned textures in use – the images might be appearing from YUV surfaces which video hardware is managing differently from regular stuff like desktop, and video hardware might be having a different set of brightness/contrast/gamma controls for those, which result in different presentation
• you have different codecs/decoders installed and they decode video with certain differences, such as with post-processing; with all the same encoded video, decoded presentation might be a bit different