Compression Discussion

[NA9D]

Re: User-requested enhancements & features?

This does cause some loss of pixels but the original resolution is maintained.

No, you don't lose pixels. Instead what happens is that because of the compression and digitization algorithms you get pixels whose values in the color gamut are not correct. All the pixels are there. They are simply not the correct values - that's all.

I could go into how image compression works but I think I talked about it in another thread.

[HeadHodge]

Re: User-requested enhancements & features?

Do you really want a device which could download what you want to watch in 10 to 15 hours and you could keep 10 movies in your library at a time?

YES!!!

Since I only watch 1 or 2 movies at a time, this would suit me just fine!!!

I don't maintain nor want a library.

[NA9D]

Re: User-requested enhancements & features?

Compression causes low value pixels to get eliminated.

No, it doesn't.

What happens in image compression is that the value of a given pixel is compared to the values of those around it. If it's the same or around a certain percentage away, that pixel is eliminated from the bit stream. However, a map of the image is created that says that this group of pixels is all the same and therefore when the image is de-compressed, all those pixels get added back in based on the mapping.

Look at it this way, if you have a screen that is entirely the exact same color on every pixel, then you could represent that entire screen with a single pixel. You could then send that pixel value across the network and send one pixel with a corresponding map that says all the other pixels are exactly the same. The decompressor on the other end, would then accurately reconstruct the image.

Now instead of that single color being the entire area of a screen of 1280 x 720 pixels, it a small area of the screen - a few pixels. Each of these small areas of a few pixels is then treated like my example of the full screen.

After re-construction - no pixels are lost and none are added. They may not be the correct value but the term "HD" says ZILCH about that. It is strictly a pixel based standard.

[NA9D]

Re: User-requested enhancements & features?

YES!!!

Since I only watch 1 or 2 movies at a time, this would suit me just fine!!!

I don't maintain nor want a library.

Hodge,

I got some new meds for you. Please take them.

Most people do want a library...

[HeadHodge]

Re: User-requested enhancements & features?

All the pixels are there. They are simply not the correct values - that's all.

I totally agree. I rented King Kong once and got Godzilla instead.

[NA9D]

Re: User-requested enhancements & features?

Should VUDU, along with the Cable and Satellite VOD providers claim that their content is really HD, when in fact, it seems to me they are doing something similar to what these players are doing?

But that's where you are mistaken. Upconverting DVD players start with content that is 480p at best. Vudu starts with 1280p resolution and goes from there.


You tell me if starting with a 640 x 480 source is that same as starting with a 1920 x 1280 source.

[HeadHodge]

Re: User-requested enhancements & features?

Hodge,

I got some new meds for you. Please take them.

Most people do want a library...

You seem a little grumpy today. Maybe we can share!!!

[redwein]

Re: User-requested enhancements & features?

No, you don't lose pixels. Instead what happens is that because of the compression and digitization algorithms you get pixels whose values in the color gamut are not correct. All the pixels are there. They are simply not the correct values - that's all.

That is what I meant by "lost pixels". I mean, it isn't like there is a black spot on the screen. In fact, any compression that isn't "lossless" is said to lose information. In the case of videos, pixels are the information.

[NA9D]

Re: User-requested enhancements & features?

You seem a little grumpy today. Maybe we can share!!!

No. It's a very good day.

I just don't know how many times I must repeat myself about this HD quality stuff!

I am tired and I've had 3 raspberry martinis tonight....

[NA9D]

Re: User-requested enhancements & features?

That is what I meant by "lost pixels". I mean, it isn't like there is a black spot on the screen. In fact, any compression that isn't "lossless" is said to lose information. In the case of videos, pixels are the information.

Well, the "lossy" part comes from having values incorrectly assigned in order to save space in the bit stream...

[redwein]

Re: User-requested enhancements & features?

No, it doesn't.

What happens in image compression is that the value of a given pixel is compared to the values of those around it. If it's the same or around a certain percentage away, that pixel is eliminated from the bit stream. However, a map of the image is created that says that this group of pixels is all the same and therefore when the image is de-compressed, all those pixels get added back in based on the mapping.

Look at it this way, if you have a screen that is entirely the exact same color on every pixel, then you could represent that entire screen with a single pixel. You could then send that pixel value across the network and send one pixel with a corresponding map that says all the other pixels are exactly the same. The decompressor on the other end, would then accurately reconstruct the image.

Now instead of that single color being the entire area of a screen of 1280 x 720 pixels, it a small area of the screen - a few pixels. Each of these small areas of a few pixels is then treated like my example of the full screen.

After re-construction - no pixels are lost and none are added. They may not be the correct value but the term "HD" says ZILCH about that. It is strictly a pixel based standard.

I'm sorry to disagree with you here, but if you compress something and it doesn't come back identical to what you started with, you have lost information. I'm not sure why you are being so critical of this point. I am 100% on target with what I said here. I chose to say it in a very understandable way to differentiate between "guessing" what the pixels might be (for upconverting DVDs) vs. losing the correct value for pixels that are less relevant to the overall picture. I agree with Hodge, you are sounding a bit grumpy here.

[redwein]

Re: User-requested enhancements & features?

Well, the "lossy" part comes from having values incorrectly assigned in order to save space in the bit stream...

Obviously, and that is entirely consistent with what I said. I'm really having a hard time understanding what point you are trying to make here.

[redwein]

Re: User-requested enhancements & features?

I am tired and I've had 3 raspberry martinis tonight....

That explains it.

[HeadHodge]

Re: User-requested enhancements & features?

No. It's a very good day.

I just don't know how many times I must repeat myself about this HD quality stuff!

I am tired and I've had 3 raspberry martinis tonight....

So you're drinking martinis and you're only giving me meds?? What a rip-off!!

The only point I've been trying to make today, is that if you take one frame of video that the studio provides VUDU and you compare that to the exact same frame that ends up on the VUDU box, wouldn't you agree that they are probably not identical???

So my proposition for a measurable metric of quality is simply the comparision of those two frames. If they are identical then it's 100% match, if they are not then it's some percentage thereof.

So I don't care how the frame is transmitted to the box, or even if it's a 100% match. I just would like to see a metric that you can use for comparing the original to the end result.

[redwein]

Re: User-requested enhancements & features?

I just would like to see a metric that you can use for comparing the original to the end result.

That's not so easy to do since the delta (number of different pixels) will vary wildly from one frame to another due to differences in the content. Just look what happens with a digital camera when you take pictures. The camera captures the same number of pixels but the file sizes vary dramatically.