Is it 4K pixels or 4K samples?

[redhead]

Hello, this is my first post on this forum. I am a little unclear on what exactly the 4K refers to. Is it the raw samples, or is the full RGB value per pixel?

In other words, is it 2K green + 2K red in one line, then 2K blue + 2K green in the next line, or is it after the raw format is converted, so there are 4K of full-color pixels per line?

[David Mullen ASC]

"4K" refers to the horizontal number of pixels. A 4K frame is typically 4096 pixels across -- vertical height (and thus total pixels) depends on the aspect ratio.

The camera has a single 4K Bayer-filtered sensor and you record the RAW output. From that, the file has to be de-Bayered to create 4K RGB files (4K for each color record). There is some controversy surrouding the issue of whether 4K Bayer ends up truly 4K in resolution -- it mainly depends on the quality of the de-Bayering algorithm. But the end result, regardless of whether you think there was a resolution hit, are true 4K RGB files after de-Bayering. Most people think the results look comparably sharp to 4K RGB scans of 35mm, which is sort of the standard. See:

http://en.wikipedia.org/wiki/Bayer_filter

I suppose there is some irony that the inventor of Bayer filtering worked for Kodak...

[Graeme Nattress]

Good answer David!

Also, the major resolution reduction is not the bayer pattern but the optical low pass filter, and this is necessary for all cameras, otherwise aliassing results which looks like awful computer graphicy stairsteps on straight sharp edges.

I like to think of the bayer pattern are particularly clever image compression....

Graeme

[redhead]

From that, the file has to be de-Bayered to create 4K RGB files (4K for each color record).
Thank you, David. That is what I was hoping to hear. I am not worried about the controversy. Just wanted to clarify whether the final result is 4K RGB, and you have clarified that.

Thanks.

[Brook Willard]

This FAQ is a good place to start: http://www.reduser.net/forum/showthread.php?t=1487

[redhead]

Oh, the FAQ was the first place I checked. The thing I was asking, not answered in the FAQ, is whether there are 4K sensors per line or whether the 4K is the final resolution after the RGB resolution.

Perhaps I should restate the question:

To obtain the 4K resolution, does it take a green and blue sample from one line, then a red and blue from another and combine them into a single pixel? In other words, does it take four samples per pixel? In yet other words, are there 8K physical samples per physical line? Four samples per RGB pixel?

Or does it take 2K blues samples and 2K green samples in one line, then 2K red samples and 2K green samples in another and then interpolate? In other words, just one actual physical color sample per pixel?

[Stephen Williams]

Oh, the FAQ was the first place I checked. The thing I was asking, not answered in the FAQ, is whether there are 4K sensors per line or whether the 4K is the final resolution after the RGB resolution.

Perhaps I should restate the question:

To obtain the 4K resolution, does it take a green and blue sample from one line, then a red and blue from another and combine them into a single pixel? In other words, does it take four samples per pixel? In yet other words, are there 8K physical samples per physical line? Four samples per RGB pixel?

Or does it take 2K blues samples and 2K green samples in one line, then 2K red samples and 2K green samples in another and then interpolate? In other words, just one actual physical color sample per pixel?


Hi,

2K Green + 1K Blue + 1K Red = 4K

Stephen

[redhead]

Hi,

2K Green + 1K Blue + 1K Red = 4K

Stephen
Thanks!

[Stuart English]

"2K Green + 1K Blue + 1K Red = 4K"

I'm sure that it wasn't meant to imply anything eles, but to be clear, that is just a simple math equation that describes the number of RAW data sampling points on each and every line of the sensor.

This is not even close to the complexity of the math that realizes the final 4K RGB samples.

[Graeme Nattress]

Yup, the complexity of the code that turns that into an RGB image is more immense than that! Also, each colour does pick up the other colours also to an extent, so each sensor is biassed towards a colour, either red green or blue but also records the rest too, at a lower level.

Graeme

[Stephen Williams]

"2K Green + 1K Blue + 1K Red = 4K"

I'm sure that it wasn't meant to imply anything eles, but to be clear, that is just a simple math equation that describes the number of RAW data sampling points on each and every line of the sensor.

This is not even close to the complexity of the math that realizes the final 4K RGB samples.

Hi Stuart,

The big advantage is that a raw file is the 1/3 size, making recording the data an easier task.

Stephen

[Graeme Nattress]

Yup, think of it as nice 33% compression that's very easy to implement in camera and you offload the complexity of reconstruction to software. Also, depending on how you reconstruct, you can get different looks.

Graeme

[laguun]

to be precise, the sensor has
Full Pixel Array:4900 (h) x 2580 (v)
Active Pixel Array: 4520 (h) x 2540 (v)
- more than 4k pixel per line.

which pixelcount you use for 4k filmrecording resolution is depending on lots of factors.
http://celco.com/FormatResolutionTable4K.asp
has a list of most of the common 4k outs.

btw - the HUGE mayority of 35mm A-budgets you have seen in the recent 10 years are 2k, not 4k. certain 2k resolutions (especially non-ana CS) are even below 1080p resolution.

The panavision/GV/sony hdcam stuff (ala apocalypto, superman, star wars, miami vice etc) is 1920x1080, slightly below 2k.

however, most 35mm projection in the cinemas don´t even show you 2k. measured most of then are 750-1100 lines, most cinemas who are already digital opted for 2k (carmike etc) - so until 4k digital projection rolls out on a large scale, the limiting factor will most certainly be the cinema&filmout and/or digital projection/broadcast.

4k mastering, shooting & post however is very recommendable. #1 you get reserves for grading, vfx, pan & scan etc #2 if you film out at 2k, don´t forget that several generations of filmcopies will be made from your master, reducing resolution every time, 4k keeps the starting level higher.

the audiences however push 1080p & 2k to the #1 position in the cinemacharts all the time, so 4k projection will only slowly pick up. unless reds announced 4k projectors aim at the cinema marketspace as well and have the red-typical competition-crushin prices.

[Andrew M.]

Many people ask me, how the heck we can get 4K horizontal RGB pixels here if we have only 1K of blue or 1K of red.

How many times I have to post it?
Each circle has RGB pixels in it even if we move one pixel offset in any direction we choose each time.

As Graeme said, it is not how it works but a good way of thinking about it this way. Geometric explanation….

[Graeme Nattress]

Yup, good explanation and diagram Andrew!

Graeme