x264 Why are faces always so bright?

[aking80]

This is always a recurring thing, but it really got to me on this encode (it's a sunny, outside video :P). Cheeks are always so bright, like a discoloring that just jumps out at you and you can't help but stare at it. I've used a basic avs script and the "Unrestricted 1pass Const. Quality HQ" preset with some modifications.


cabac=1 / ref=5 / deblock=1:-1:-1 / analyse=0x3:0x113 / me=umh / subme=7 / psy_rd=1.0:1.0 / brdo=1 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / chroma_qp_offset=-4 / threads=3 / nr=0 / decimate=1 / mbaff=0 / bframes=4 / b_pyramid=1 / b_adapt=1 / b_bias=0 / direct=1 / wpredb=1 / bime=1 / keyint=300 / keyint_min=30 / scenecut=40(pre) / rc=crf / crf=22.0 / rceq='blurCplx^(1-qComp)' / qcomp=1.00 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / pb_ratio=1.30 / aq=2:1.00 (taken from mediainfo)



<input>
<deinterlace>
HQdn3D(3)
undot()
<crop>
<resize>


^Sorry don't remember the fill in details of the script, but you get the idea. Basic script made with megui with HQdn3D added by me.

Here's a 1min sample of the encode. I can rip a vob of the DVD if wanted (around 200-300MB or so). Check out mostly the girl on the bike and the girl running in the street, the coloring just jumps right out :confused:

http://www.mediafire.com/?tzdtxtfanhv

[Comatose]

Did you try encoding unfiltered? Also, please show a before and after (images) :x

[F J Walter]

It's hard to speculate about the cause without actually seeing an example, but perhaps it could be something like this. Or maybe I'm way out.

If the faces are slightly overexposed, this effect could become more noticeable due to x264's tendency to smooth grain or noise at moderate bitrates where there isn't the bitrate to encode the grain accurately. Thus the gradient, and the sharper edge on the 'highlights' of faces are more noticeable.

This might be more apparent with film-source as opposed to digital source as film, with its smooth tail off in dynamic range, encourages higher exposures on faces as it looks pleasant and film-like, but part of that is having other subtle cues it is film, like grain.

Edit: just looked at your sample clip. Yes, I was right I reckon! Film source, heavily overexposed. Actually it looks like that bright, contrasty, overexposed effect is what the cinematographer was intending. I think the compression at moderate bitrates removes some information that is hard to compress and not usually noticed, like grain, but makes edges around hot areas (like the highlights on the face) look less natural (actually, just a bit less like film, but overexposed film looks natural to us).

Do you think it is improved to your eyes if you add subtle grain after decompressing, a good quality filter and very subtle, of course?