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4k DI but shot in 2.8k (3 replies and 5 comments)

Dvdmike
7 years ago
Dvdmike 7 years ago

Does this effect the image quality?

Obviously a professional 4k upscale is better than a on the fly upscale but does the gap from the raw to the DI make a change on how the finish looks?

Mind you most CG is finished at 2k also, how many shows are 4k end to end and does it make a diffrence?

Morris
7 years ago
Morris 7 years ago

4K or 2.8K both are an illusion to start with.
Those terms refer to the total amount of pixels on a single image line on the sensor.
We do have to realise that we don't have 4K for the Red image, Blue image and Green image; we have 4K for them combined. So the green image on a 4K sensor is a mere 2K, Red and blue are both 1K; rendering very blurry images. (So a three sensor HD camera in fact has a lot more pixels than a cinematography camera...)
To restore some sharpness,we use debayering: a software process to "fill in the gaps".

So normal 4K images or 2.8K images have already been upscaled by debayering. An extra upscale, therefore, isn't that big of a deal..

Futhermore; debayering is just one of many aspects affecting sharpness.
Motion blur, for instance, can be a real dealbreaker. In normal moving images (24fps at 180d shutter), the amount of motion blur limits the perceived sharpness at about 2K. So with normal action (actors and/or camera moving) you can rarely notice a huge difference between 2K or 4K images.
It's not without reason "The Hobbit" was shot at HFR (48fps)... Which meant shuttertime could be reduced and less motion blur was noticeable: more sharpness in the end.

A whole different question then becomes: do you like smooth moving images that are extremely sharp ? But that's an aesthetics discussion.

Oneris Rico
7 years ago

The hole point of the Bayern pattern is to have a great diagonal resolution on the green channel (also referred as lumma channel) this information is them interpolated with a lot of science, so we end up with a lot more than a 2k signal out of a 4k sensor. That's why Sony's f65 sensor is so interesting.

Going back to the question, this is what arri did with their UHD format and it will definitely feel sharper than their 2k. To say will it make a difference or not deppends on the viewing conditions, if is a huge screen it will, or not? Roger used 2,8 for IMAXs version of Skyfall and worked very good

Morris
7 years ago

You're absolutely right.
I oversimplified in my (mis)calculations. I do apologise.
The green channel in a Bayer pattern is in fact roughly 4 million pixels, which is somewhere in between 2K and 3K.
I didn't want to suggest the Bayer pattern is a bad thing.
In fact, I tried to use it as an example of good science helping us to insure sharpness.
So any good interpolation science will help. (which should have been my answer to the original question...)
I couldn't resist trying to make the point that 4K is a difficult subject.
Nowadays 4K seems a scientific term that suggests a level of quality, but it's, in fact, not that simple.
You mention a great camera.
The F65 has everything going for it: it has 8K in resolution on the sensor, great interpolation science and thus "very good 4K" whereas Sony A7s' 4K is a whole different type of resolution.

Oneris Rico
7 years ago

No need for apologies at all!!!

Also f65 sensor is tilted 45 degrees so you have a 8k resolution in the green channel (with a unique fill factor), it is absolutely ridiculous! But I do agree with you that most of the 4K cameras are in fact way lower resolution than advertise, it is funny when let's say Black Magic offers a

It also worth noticing that on paper a three chip sensor will outresolve any bayer pattern camera, but when you take into account all the different MTF from all the elements in between then it's not so true, you will have 3 OLPF, 3 IR cutter, a prism, one traslucid mirror...

Morris
7 years ago

Very good point !

Dvdmike
7 years ago
Dvdmike 7 years ago

I get the diffrence, but its  still an upscale, just not one on the fly.

IMAX DMR is all kinds or wrong to me, I admit it's come a long way from Apollo 13 but its not like most IMAX cinemas are state of the art now 

Roger Deakins
7 years ago
Roger Deakins 7 years ago

I tested the difference in image quality between a 2K and a 4K DI when shooting 'In Time', which was shot on the Alexa in Uncompressed HD. I felt there was a substantial difference between the two and that is my argument for finishing in 4K.

Dvdmike
7 years ago

Thanks for the answer sir

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