Split Compression

[Guy]

After reading this post:

http://www.reduser.net/forum/showpos...9&postcount=38

I took a closer look at this image(48MB TIFF):

http://www.hdforindies.com/uploaded_...02_001_OCN.tif

After messing with levels and looking at the blue and green channels by themselves there is a noticeable change in the texture of noise in the sky between the top half and bottom half of the picture.

The change happens exactly(to the pixel) in the middle of the picture and is visible on both sides of the car.

To me it looks like that the top half of the image and the bottom half are being compressed independently of each other. It is probably much more apparent on images like this one where the top half and bottom half are very different.

I wonder if this is baked into the hardware of if it is something that could be changed with different firmware.

Graeme?

[Michele Gavazzeni]

Probably the amount of data generated by the sensor exceed the bandwidth available from a single processor
in these case it could be handled by two separate chips one for the top half one for the bottom half.

In these case something isn't working properly giving different results.

it looks like the image has been processed with a soft median filter

Maybe an adaptive noise reduction filter is applied when capturing
so if like in these shot:
the top part is mainly sky
while in the bottom half has more elements with different colors and noise patters.
In these case an adaptive filter would have read two different scenarios applinig different corrections!

This joust an idea i've no knowledge about how Redone really works.

[Ryan Sims]

Here's my guess: The top half of the frame is mostly blue with very little detail. The blue channel got most of the bandwidth there, hence more detail in the blue channel as seen as grain. The bottom half has very little blue and lots of detail, so the red and green channel got nearly all the compression bandwidth. Blue didn't need much info for the bottom. Good info to know if you plan to do green or blue screen VFX work. Up until last week, I think most of us had never worked with 4K moving picture files (even though I'm just playing with files you guys have posted). RED truely is 4K for the masses!

Here's the images we're talking about:




That came from the uncompressed file of this:


It would be best to also read this whole thead as well:
http://www.reduser.net/forum/showthr...?t=4330&page=5

[Miltos Pilalitos]

I have noticed the same thing way back when the first frames from "Crossing the line" were posted. I didn't want to mention it back then because it was from a beta camera.

I don't think the reason is that one particular channel is taking all the bandwidth. You can see the same effect in the following frame even if you don't watch a particular color channel. Observe well...


For a full frame: http://www.red.com/skin/img/gallery-still/009000.jpg

the split is exactly on the middle of the frame!

[Luis Otero]

De-Ja-Vu from JVC Split screen issue?

[Ryan Sims]

Here's a split example in the City file as well:


You have to tweek the contrast really hard to see it.

[Miltos Pilalitos]

De-Ja-Vu from JVC Split screen issue?

Are you suggesting that Mysterium's secret is that it's actually 2 CMOS Chips?

[Luis Otero]

No, I am not suggesting anything. It is just a surprise issue that we went through JVC HD camera... The technical explanation must be given by RED, and I am not associated with them at all (just RED resrvation # 711).

[Guy]

You can also see it here in the blue channel of the Garage TIFF(this is without any kind of manipulation), 100% crop:

[Miltos Pilalitos]

Hmm.. interesting...

Before you post this i thought that the upper part was always the grainy one and the lower the softer but in that pic it's seems that the contrary is also possible.

Strange!