[MPlayer-DOCS] en/mplayer.1: bugs and question

[Guillaume POIRIER]

Hi,
Le ven 01/10/2004 à 12:26, Torinthiel a écrit :
> On Fri, Oct 01, 2004 at 11:00:10AM +0200, Guillaume POIRIER wrote:
> > > Is there meaning of DC a low resolution part of image? Allways is?
> > > 5875: ...scplx_mask will reduce the quality of P blocks even if only DC 
> > > is changing
> > 
> > I don't understand what you mean... but if your problem is to understand
> > the meaning of DC, I can't help you with it right now, I don't know.
> 
> To tell what DC is you first need to know a little about JPEG ;)
> JPEG is basically image transformed to YUV colorspace, divided into 8x8
> blocks (sometimes U and V planes have larger blocks) and each block is
> then subject to discrete cosine transform. Now the DC is the top-left
> coefficient after that transform. So DC being a low-res picture is not
> that far from the truth, but it also contains some information about
> other pixels in this block. It's the single most important coefficient.
> And in MPEG it's the same - I frames are more or less JPEG images.

Could you give a simple example to understand what a DC change could
mean (I guess that we can't throw your nice explanation at our Joe Users
;-)?
A fade-in or fade-out maybe? 

Guillaume