H264 compression too bright?

[DavidBeier]

I was trying to output some HVX200 files from Avid Xpress Pro HD 5.23 and found that when compressing in H264, the image ended up being brighter than it origionally was. What was really irritating about this is that it seemed to make the noise in the shadows suddenly pop out to an unacceptible level. Anyone else notice this and can recommend a way to get around it? It looked fine when I exported it uncompressed (and took about 1 gig for 15 seconds).

[Relevant Chris]

I just encoded out to H264 as well and had the same brightness results. I have also noticed that when I encode to MPEG2 for DVD the picture ends up being darker than it origianlly was. I'm not sure why. What are the correct black levels for dvcpro hd? 7.5 or 0 It may be a difference in that particular setting. Any help on this would be appreciated.

[dougspice]

Sounds like a gamma problem to me, which should be correctable in the encoder.

[electricpig]

If you keep the same codec throughout the process (ie DVCPro HD) then they'll be no gamma issues. This includes taking the footage through Final Cut, and Shake (which is a gloriously notorious gamma-shifter).

I've then rendered my final out of Final Cut as DVCpro HD so I have a same codec master. Render as RGB must be clicked in the render settings in FCP.

I found that compressing the DVCPro HD master to Sorenson3 from QT Pro gave me a heavy gamma shift, but that H264 was almost identical to the original. This was good news, and good for web etc.

But then I then burnt from the DVCpro HD master to DVD using Toast, played back on TV and had a heavy gamma shift again. Not good.

It seems that Apple has an internal DV gamma shift going on...

I've got around this by getting BitVice:
http://www.innobits.se/index.php

Now, this is a costly encoder at £200, but as a time saver and quality encoder it's invaluable and beats the quality of the Apple mpeg2 compression.. It's got a gamma 2.2 correction option aswell as other options and gives me an un-gamma shifted mpeg2.
I was able to import the BitVice mpeg2 & aiff file into DVDStudio Pro (Toast should instead here aswell) and burn to DVD.

So I now see the same on my HVX as I see on my Mac (I'm running it at 2.2 gamma instead of 1.8), and on DVD too and I'm a happy bunny...

[Jim Arthurs]

This is an annoying issue... I see it with Sorenson QT exports as well... usually I just adjust the gamma to compensate, but am never sure if I'm messing it up for a Mac viewer vrs. a PC guy... or vice versa.

Here in this thread, notice how the still image export has more punch and solid blacks compared to the Sorensons... these QT's are without any adjustments to compensate.

I'm curious if the QT's look right on the mac if any users out there care to download and compare... seem wrong on the PC...


http://www.dvxuser.com/V6/showthread.php?p=564103#post564103

Regards,

Jim Arthurs

[Tunnell Mill]

I have been having the exact same problem with H.264 being brighter than the original footage. I notice my blacks are grainy and the image appears much brighter.

[cinemakinoeye]

I was observing some gamma problems when I ran compressor directly from Final Cut Pro, and then I tried exporting a reference movie and runnning compressor independently of Final Cut and the gamma problem went away. Twilight Zone experience, still not 100% sure why this was the case.

[Tunnell Mill]

Quick question: I opened an H.264 movie in Quicktime 7 and noticed that you can change the aspect ratio, size, etc., and save it. But my main concern has been the brighter image after exporting to H.264 out of Final Cut Studio. In Quicktime 7, I opened the Audio/Video settings and slightly adjusted the brightness and color to where it looked exactly as the footage did in the FCP timeline - however, I did a save as, trying both "self-contained" and "reference" movies and the image reverted back to the bright image. I can actually fix the color and brightness, but can't save the fix! Any suggestions? Or any suggestions in general on how to export out of Final Cut Studio as H.264 without the image jumping much brighter? In short, how do I export to H.264 and keep the color/brightness consistency of the original timeline?

[ggdelarge]

anytime you compress, the image will look a little different. You can change brightness and whatever you wish using cleaner. i think you can also change brightness, etc in compressor

[electricpig]

Tunnell Mill, in my Final Cut /System settings/Playback control/Gamma correction I'm set to approximate as I found my Graphics card on my Quad was screwing around with the gamma a bit when it was set to accurate.

Also in the sequence settings, for video processing I'm set to always render in RGB.
YUV sets the white and black points to 16 and 235 rather than 0 and 255 which can cause a density change on rendering the QT.

I'm tending to render out to a DVCPro HD master QT, and then make my versions from there, ie PAL, web, 720P etc.

[Tunnell Mill]

electricpig, this was very helpful and rendering out to DVCPRO HD kept the image pretty much the same as in the FCP timeline - which is much welcomed after having the image jump 50% brighter previously. the colors are now strong and the image doesn't look any brighter. however, in QT, i did a "save as" after i adjusted the image size (i wanted it sized down to about 640x320 so i could put the file up on my website. perhaps i rendered out to the wrong setting...the movie was HUGE but retained the nice colors and look. after "fetching" the movie up to my file manager for my webpage, and upon looking at it there, the movie appeared severely "squished" - the aspect ratio totally off, although i saved the file as a much smaller image. the other thing is, by resizing the movie in QT, when i saved the movie as a "reference" movie, the Fetch transfer was quick - lightning speed. but this is the file i looked at in my file manager and it was severly squished to the left portion of the viewer screen - almost like it wanted to put it into a SD format as opposed to widescreen. so then i attempted to Fetch the untouched DVCPRO HD movie up to my site and it said it was going to take like 24 hours or more just for a ONE MINUTE movie! so, i cancelled that Fetch not knowing if it would squish, too, or if it would be too large to fit on my main webpage. after all, viewing the the DVCPRO HD movie in QT almost took up my entire computer monitor.

so, in summary: the render out of FCP to DVCPRO HD fixed my brightness problem and the footage looks great. i am stumped why i can't down-size the movie in QT and save the change and then upload the smaller image to my website? maybe i can, i'm just doing something wrong??? or, how do i fix the "squish" problem i'm having?

the main goal is to upload my little clips, trailers, etc., to my website...have them be in widescreen type mode like you see most all the HVX clips uploaded on the DVXUSER.com site, yet retain the strong colors that are close to the original footage on the FCP timeline. i've seen so many clips here on this entire forum of HVX footage that look exactly like what i'm trying to do, but can't seem to find the right knowledge of how to upload to my site and have the footage look very close to the stuff in my FCP timeline.

thanks for any more help.

[DavidBeier]

Any help for those of us using Avid to export?

I'm using it to export H264. I can't find any controls for the gamma. I already have it set to RGB. The uncompressed still looks perfect but H264 is noticibly brighter and most of all it appears to be boosting the noise (which is what makes it so frustrating). Anyone who's found good settings in Avid?

[otari_99]

This is really interesting. I experienced the same issue a couple of years ago on my SD Matrox system. I tried different encoding strategies, but never did adjust black reference level. I actually limited the other end (I know, Kinda' goofy). It was frustrating because my analog levels out to tape were already broadcast acceptable. Even my audio levels were encoded too hot to DVD! So, I ended up with two projects on my system. There was one for DVD, and the other for tape (broadcast).

[DavidBeier]

Man this is annoying. One of the things I LOVE about pure digital is the hope that we wouldn't have to deal with the same kind of crap we did with film and worry about how the image will degrade over multiple generations and alter our shooting methods.

[electricpig]

Tunnel Mill, glad that helped to fix your gamma issues.

When exporting from Quicktime Pro, in settings set to H264, compression at medium (50%) at a minimum or else it gets too blocky (halfway between medium and high is better if you can handle the larger file size).
Automatic keyframes, automatic data rate, best quality encoding.
In your size set your required size as custom (the size you gave will distort (squish) the aspect ratio as it's a 2:1 ratio, whereas we're working 16:9 from the HVX - Better would be 640x360).
You can work out scaling sizes with 'the rule of 4's':
1080 divided by 1920 = 0.5625, multiply this by 640 gives you the missing figure, ie 360

1920 x 1080
640 x ???

(Of course you can replace the 640 with any width you want and it will always generate the value for the height.)

You can take your sound down to 20.1 hz, but don't go below 16-bit otherwise you get fizzes and crackles added.
Then click 'Prepare for Internet Streaming' with a Fast start.

Export as a self-contained movie and it will stand by itself, if you export as 'referenced' then it will be tiny, but will always require the original file you exported from in order to play.

Do all this and you should be OK.

mike.c