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Jean
12-16-2003, 02:58 PM
Hi.
Last morning I woke up with a weird idea.
And if the lossless format was lossy ?
If all I knew was a lie?


So I began a series of test with all lossless codec formats I know.
RTV, Digisuite mjpeg lossless, Huffyuv, Alparysoft, Picvideo jpeg lossless.

And here are my results.


I started with an original RGB colour/shape test file found on a website (I don’t remember the address), which I compressed in :

RTV (in afx with newtek’s I/O plugin on a non toaster machine)
RTV (in VT3)
Digisuite Mjpeg lossless
Picvideo jpeg lossless
Huffyuv 2.1
Alparysoft
And
Lossy Mainconcept DV 2.10 (for fun)


(See here
http://www.ombres.com/html/body_download.htm
for zip file, comparison pattern pics are middle quality jpg but the others are highest jpg quality (accurate enough).

The difference pattern shows which pixels are different. Black=no difference / white = difference. colours = less different but still.


We can see the destructive power of 4.2.2 on RTV, Digisuite and Mainconcept when picvideo, Huffyuv and Alparysoft show no loss at all. They Seems to use RGB (4.4.4) when the source is in RGB.


After that, I tried the compressed videos as source to see if we’re having the same results between 2 generations of the same “lossless” codec.

Well, for that I used “difference” mode in after effects with “Equalize” to enhance the luminosity of the result for human eyes to see.
Can u imagine my surprise when I discovered that there is a difference between first and 2nd generation with RTV and Digisuite codec with a preference for the Digisuite which shows fewer approximations.
There is absolutely no alteration of the image thru generations with the others lossless codecs.

You can do the tests at home using the images in my .zip. I put a screenshot of my AFX comp if you need it.


For info, here is the Size for 5 sec of video in Mo:

Mainconept dv : 17.584
Digisuite : 38. 140
Picvideo Lossless Jpeg : 52.179
Huffyuv 2.1 : 61.644
Alparysoft : 66.700
RTV : 101.251
Uncompressed : 151.881


Troubleshoots:

-I tried Alparysoft on my VT3. Decoding is Ok, but the encoding results in a desperately black image.

- Digisuite codecs don’t work on VT3, it’s even forbidden to install them on a toaster system.


Conclusion :

For now on I’ll be careful not to make more than 2-3 generations with RTV.

I’ll try to use picvideo’s jpeg lossless codec when doing multiple renders of the same source. I need it when working with our VT3 (capture-edit)+3d station+2d compositing station+go back to the VT3 to print the final render.
The only problem is the "CPU time consuming" of this one, only 3 layers in TED and I’m reaching 80 % of processor use on bi-3.06 xeon system.

Digisuite codecs are potentially the best, because they are the lightest in terms of Mo/s. 2nd in encoding time behind RTV. Even if they’re not perfect in terms of re-compression (multiple generations) the loss isn’t that bad.
Finding a way to make this one work in VT3 would be wonderful.

That's all folks.

Paul Lara
12-16-2003, 04:07 PM
Thank you for posting your research efforts, but it is important to clarify your interpretation of those results:


RTV is lossless, but it is handled in a completely different colorspace (YUV 4:2:2).

Unfortunately, your tests were performed by running through After Effects, which repeatedly converts to and from RGB, which will inevitably cause slight problems.The reasons you are seeing ‘noise’ in the difference pattern between RTVs is that NewTek performs dithered RGB-to-YUV color conversion, which gives perceptually superior results on video playback.

Jean
12-16-2003, 05:09 PM
Perhaps I wasn't clear enough when I said that the other codecs used no conversion from RGB source.

QUOTE:
"We can see the destructive power of 4.2.2 on RTV, Digisuite and Mainconcept when picvideo, Huffyuv and Alparysoft show no loss at all. They Seems to use RGB (4.4.4) when the source is in RGB."

I made rendering test in VT3 from rgb source to rtv. I understand the difference pattern I get from that with RGB --> yuv conversion.

I'm relieved knowing the RTV's Lossless integrity when using YUV 4.2.2 sources now.

Even if I don't understand the "Dithered RGB --> yuv colour conversion" thing, when encoding in VT3. :-/

Anyway, Thx for your shedding light on that, Paul.

Aegis
12-16-2003, 05:36 PM
Even if I don't understand the "Dithered RGB --> yuv colour conversion" thing, when encoding in VT3. :-/

I could be wrong but I believe this means that when RGB video is imported into the VT[3] environment it is automatically dithered to compensate for the more restricted colourspace that YUV works in... Hey Paul - how'd I do? :p

Jean
12-16-2003, 05:54 PM
The thing is that the 2nd generation RTV comes from a 1st generation RTV supposed to be in YUV 4:2:2 too.
(Rendered in, VT3 of course)

So why the dither from yuv to yuv ?

Apart from that, if I understand well, it's still not advised to do several generations RTV in AFX "which repeatedly converts to and from RGB".