Theory on Squeeze Mode

Wiyum

Active member
First, sorry if this is in the wrong place. I figured it'd be best discussed here because this is where the DVX-100A discussion has been, and this is only relevant for the DVX-100A.

Squeeze mode may in fact offer anamorphic images of nearly identical quality to that of the anamorphic adapter. It is still a hit, but a slight one, resulting in an image utilizing 97% of the nessesary pixels instead of 84%. It all comes down to how the DVX-100A handles image processing, which is anyone's guess. To explain:

A minidv image is comprised of 345600 pixels, arranged 720 x 480. The DVX-100 (both models) takes an image with 410000 pixels (roughly 739.36 x 554.52) and downsamples the image to 345600. The 16x9 area of the DVX chips utilize all 739.36 horizontal pixels, but only 467.8 of the vertical pixels. With the matted 16x9, this figure didn't much matter... the 467.8 pixels were added to the dead pixels of the initial 554.52 on the chip so that the resulting image wouldn't be skewed: the image needed to be 4:3, so the image area was only 405 pixels tall, the other 75 pixels being dedicated to matting. But if the squeeze mode downsamples to 720x480 by only scanning the center of the chip, ignoring the unused pixels out of the 16x9 area altogether, then it can make its downsample using 467.8 pixels to generate a 480 pixel tall image. Not quite perfect, but certainly better than the previous post-stretching technique which created its vertical resolution based on 405 pixels.

Maybe I'm crazy, and I'm certainly no engineer, but is this possible? I just realized that the DVX-100 chips oversample and downconvert to 720x480, so I figured it may in fact be the case that the anamorphic area used in squeeze mode has nearly 480 vertical pixels to use. It doesn't quite, but it is frighteningly close.

Of course, squeeze mode may just be doing the same thing we do in post-stretching, and it may downsample the whole chip's image to 720x480 before stretching. Anyone know how we can determine this when the camera is released?

Will
 
Re: Theory on Squeeze Mode

I actually was discusing this with a friend last night.. If that is the way they do it, then you are totally correct. Remember though that the CCD only has 380,000 effective pixels, but that still has enough for 100 or so lines of overlap.
 
Re: Theory on Squeeze Mode

For 380,000 pixels, it would be 93% of the neccessary pixels rather than 97. Still much better than 84!

Will
 
Re: Theory on Squeeze Mode

Well if you used a PAL version you would get even more resolution. With the "old" dvx you get 720*432 in the 16:9 area of the picture. Sp if you theory is correct the DVXA would bring you much more resolution.
 
Re: Theory on Squeeze Mode

The 'A' doesn't add any resolution... it would extract the central portion of the CCD and then stretch it up. I expect the in-camera 16:9 mode to deliver a picture very comparable to the stretch-it-in-post method in Vegas.

But then again, we'll see when the camera arrives...
 
Re: Theory on Squeeze Mode

I know the A doesn't add resolution, but since the native resolution of the camera is already higher than minidv, the resolution of the squeeze image could, in fact, be very near the resolution of minidv. I guess we'll see soon enough.

Will
 
Re: Theory on Squeeze Mode

yes, I totally afree Wiyum, that is my take on it, theoretically it should be possilble.
 
Re: Theory on Squeeze Mode

Yes, we shall see, soon enough. But I still think that you're going to be looking at a 25% resolution loss, with a maximum possible resolution of 360 lines from squeeze mode.

(of course, I was dead wrong about the existence of a DVX100A in the first place, so I could be dead wrong about this too!)
 
Re: Theory on Squeeze Mode

I don't follow; by my math, non-squeeze mode still gives you 405 lines to play with; theoretically squeeze would be even more than that. Where does 360 come from?

Will
 
Re: Theory on Squeeze Mode

Because 405 is the wrong number, due to the aspect ratio.

DV is not square pixels, so you can't say that 720 x 480 is a 4:3 ratio (just look at the math... 720:480 is actually 3:2, not 4:3, yet the 720x480 picture fills a 4:3 television). It's because the pixels are not square, they're taller than they are wide, so more of them fit on a line. A true 4:3 ratio using square pixels would be 640 x 480, but DV is 720 x 480, thereby cramming more pixels per line, which means that they are slightly skinner.

So if you use 720 x 9 / 16 as your formula to determine the height of a 16:9 DV image, you'll come up with 405 -- which is wrong, because 720 x 480 is not the square mathematical ratio. You have to use the 4/3 of the height, which is 640. So the proper formula is 640 x 9 / 16, which yields 360 scan lines.

So if you employ squeeze mode, the central 360 scan lines will be extracted and stretched to cover the 480-line height of the frame.
 
Re: Theory on Squeeze Mode

the pixels are rectangular.. Are you sure your not talking about horizontal resolution instead of vertical?
 
Re: Theory on Squeeze Mode

His reasoning and math check out... I've been mistaken. And actually, I knew nonsquare pixels would be the problems with my math, but I never realized how to figure out the "more precise" math.

Will
 
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