I need advice on virtually lossless codecs for archiving

[schmoppa]

Thanks to everyone!

I now need to re-evaluate the situation and figure out what the best course of action is.

[dwiesel]

junkmalle...you touch on YUV2 and YUY2...can you please explain the difference between these two formats? They are used so interchangeably that I'm not clear on what separates them...I think one thread said they were the same thing, but from what I've read I'm thinking they're not.

...also what happens as far as quality loss when saving a YUV2 AVI to an YUY2 AVI? I've done this and my YUY2 file is smaller in size (red light for quality loss). Many thanks for any enlightenment.

[junkmalle]

dwiesel,

you touch on YUV2 and YUY2...can you please explain the difference between these two formats?

YUV refers to the color system which separates video into 3 components, Y (intensity, same as black-and-white TV), and two color compoents, U and V. It takes all three compenents to fully describe the color of a pixel (just like RGB requires three components).

YUY2 uses the YUV system to describe a video image but only uses half as much color information as intensity information. So rather than having all three components for each pixel there are only two, but the pairs alternate between Y+U and Y+V. For example, four consecutive YUV pixels look like this:

YUVYUVYUVYUV

Encoded as YUY2 you get this:

YUYVYUYV

Notice that each Y is surrounded by both a U and a V so you can make each pixel full color but the final resolution of the color information is half that of the intensity.

The origin of this scheme is in color television. To keep the signal compatible with black-and-white TV they came up with the YUV system (BW TVs only show the Y portion of the signal). And to keep adjacent TV channels from interfering with each other they had to reduce the bandwidth of the color information.

The reason the YUY2 reduction works fairly well is because your eyes havd fewer color receptors than intensity receptors. You don't see colors as clearly as intensities. If you watch TV from far enough away you don't notice that colors are smeared. If you get up close you see it of course.

what happens as far as quality loss when saving a YUV2 AVI to an YUY2 AVI?

If you are starting with a full YUV or RGB source (say, a computer generated animation) then you will lose color detail. But analog broadcast TV, cable, and satellite are already in a YUY2 format so you don't lose anything (except the usual A/D conversion losses). DVD is encoded with MPEG compression which uses YUY2 format (or something similar) internally, so even if a film was captured in full YUV or RGB color, what's on the DVD was reduced to YUY2.

[dwiesel]

Very informative!! I'm guessing the 4:2:2 reference I've seen when researching this refers to the pattern you used as an example. But I'm still fuzzy on the YUV2 which you didn't make mention of....would that be "YUVYYUVY", and how does this differ from YUY2 in performance and usage?

For my purposes, I'm capturing from a laserdisc (as composite) as a YUV2 AVI...and since I will be saving the captured YUV2 AVI to a YUY2 AVI, am I getting any "loss" per se, or should I avoid this?

You say I will obtain loss when my source AVI is YUV2 or RGB and I'm saving as YUY2...wouldn't I get less if my source were YUV2, since it uses the same colorspace as YUY2? Would my best scenario be to capture in YUY2 and save in YUY2?

Sorry to be a pain, and thanks (how did you learn all this, seems like a person needs a degree in it!)

[BJ_M]

if you cap at YUV2 - don't convert it ..

[dwiesel]

BJ_M, unfortunately I have to convert it for several projects, and the only choices Pinnacle offers is YUY2 or RGB24...so I'm thinking I may be better off using a third party software.

I've tried VirtualDub, but I don't understand why my new AVI file is less in size if I'm saving to the same format...makes me think I'm losing info/quality. And the bitrate changes as well...is this a good thing?...I have so much to learn and I thought I new some.

[junkmalle]

dwiesel

I'm still fuzzy on the YUV2 which you didn't make mention of

I don't really know about YUV2 -- but I did a little google search and it seems to be quite similar to YUY2.

http://www.bitjazz.com/sheervideo/about/faq_formats.shtml

It appears the only significant difference is that YUV2 has a greater range of values then YUY2. They both use 8 bits per component but YUY2 is limited to the valid video color space (not all possible combinations of Y, U, and V are valid in NTSC and PAL video). YUV2 uses 8 bit signed integers (-128 to 127) to encode U and V, whereas YUY2 uses 8 bit unsigned integers (0 to 255) -- note the range is the same (256 different values, just treat the YUY2 values as signed and subtract 128 to get the the equivalent YUV2 value, or conversely, add 128 to the YUV2 value to get the YUY2 value).

I will be saving the captured YUV2 AVI to a YUY2 AVI, am I getting any "loss" per se

Since your source is a laser disc it shouldn't have any invalid YUV combinations (ie, outside the range that YUY2 is limited to). So converting to from YUV2 to YUY2 shouldn't cause you to lose anything. Even if the YUV2 data has some invalid colors, they will probably be passed to the YUY2 output. Of course it's up to the details of the converter code.

how did you learn all this

Just picked it up over the years...

[dwiesel]

Thank you so much for your time and explanation...it goes a long way in my learning curve.

[junkmalle]

You're quite welcome, Dwiesel.