Red One Measured Resolution

[Dave Blackham]

Are there any figures for the measured resolution figures for Lines per image height and horizontal resolution for a Red One Camera. Assuming a properly collimated and very sharp lens is used so the optics exceed the sensor performance.

Thanks,

Dave Blackham
UK

[Graeme Nattress]

On 4k (4096*2304) recording I can see about 3.2k measured resolution, or 1800 l/ph. Someone on CML reported similarly.

Graeme

[Steve Sanacore]

I am confused why you don't resolve 2304 (vertical axis) lines at 4K? If you divide the horizontal number of photosites (4096), by the horizontal size of the sensor (24.4mm), you get 167.9 pixels (or lines) per mm. Would this be the maximum resolution for this sensor? Am I doing this right? I wonder how this compares to film and how it could help specify lens requirements, if at all?

Just my inquisitive thoughts..

[Andrew M.]

Vertical l/ph is bit confusing for digital Bayer sensors.
It comes from TV cameras world.
4K format is 4096 pixels horizontal.
Vertical pixels are different for different formats.
2:1 format will have 2048 vertical pixels and 2.39:1 will have 1714 vertical pixels.

RED CMOS sensor has 5.5 micron pixel size, so using simple mathematics you should have, to be on safe side, lenses that deliver 200lp/pmm at 50% MTF

[Dj Joofa]

On 4k (4096*2304) recording I can see about 3.2k measured resolution, or 1800 l/ph. Someone on CML reported similarly.

Graeme

Was that for a perfect registration of line pairs with photosites -- I mean to say was Kell factor taken into account?

[Graeme Nattress]

It was measured with linear sinusoidal 4k zone plates.

The reason you don't get the measured resolution as the same as the sensor resolution is that if you did, you'd get massive aliasing and a nasty image. How does it compare to 35mm film? Easy - superior.

Graeme

[Graeme Nattress]

Joofa, Kell factor is a display phenomena, where the perceived display resolution is less, some factor usually around 0.7 of the actual resolution. It is effected by the type of display, like the CRT's gaussian spot distribution, or the pixels in an LCD display.

Graeme

[Deanan]

Was that for a perfect registration of line pairs with photosites -- I mean to say was Kell factor taken into account?

Are you talking about resolution extraction with perfect registration without a lens or OLPF?

These tests were with a lens and OLPF as is standard on the camera with no attempt made at aligning the chart.

[David Mullen ASC]

It was measured with linear sinusoidal 4k zone plates.

The reason you don't get the measured resolution as the same as the sensor resolution is that if you did, you'd get massive aliasing and a nasty image. How does it compare to 35mm film? Easy - superior.

Graeme

So what would be the maximum potential resolution of something recorded 4:4:4 HDCAM-SR? Would it matter what type of sensor was being used? For example, the 12MP RGB striped sensor of the Genesis versus three 2MP HD sensors in the F23? Does "oversampling" in regards to using bigger sensors help improve resolution even when recording to 1920 x 1080 RGB? Or do you always hit the same limit? Or is the advantage in that case, larger sensors with more photosites, more in terms of reducing aliasing? Or can you use a less strong OLPF with a bigger sensor with more photosites? Or do you need a stronger one?

[Graeme Nattress]

It's like this....

You need an OLPF to avoid aliasing, as aliasing is an unwanted artifact.
OLPF's are slow filters, in that to get serious attenuation at high frequencies, you've got to start them early.
Electronic filters can be as fast or slow as you want - but you trade factors of resolution, aliasing, ringing and edge sharpness.

So, if you have a camera, and tell me it's sensor is 1920x1080, and you can measure good MTF out at 1920x1080 resolution, it must, by definition, have significant aliasing out at that resolution. That's not good.

So, what's the "solution".

Best is to use good optical filters and have more that enough resolution, so even though you loose some through the filtering, you've still got more than enough. That's the RED "solution". You can always downsample, and choose that downsample filter to go to a lower resolution with as much or as little detail in that resolution as you want, trading the factors I mentioned above.

If you start with a lower resolution, you're going to want to keep as much of that as possible, and not be as aggressive on the OLPF, and let in some aliasing. But you don't have enough resolution to do much downsampling.

The smaller the pixels, the weaker the OLPF you need as the MTF of the lens will be much lower at that higher lp/mm. If you can get the resolution high enough so that there's little or no MTF at that lp/mm, you don't need an OLPF. We're not close enough to that yet....

I'm not, personally, keen on an RGB stripe pattern. If you're going to a single sensor approach, the bayer pattern has proven itself time and again. If you're resigned to downsampling to 1920x1080 anyway, I'd do a bayer pattern, demosaic to the 12mp resolution, then downsample with user definable downsample filter to the 1920x1080. But that requires serious horse power to do properly. But that would give you the best result from the conditions of a single 12mp sensor with camera output fixed at HD rez.

Graeme