DCP- from Scratch ( workflow ) ?

[Dan Hudgins]

- so inside Scratch, i wanna set all my DPX files as Gamma 2.6, so how about the LUT ? should i apply it or no ? and if it should, Whut most LUT commonly used for DCP transfer? based on my DPX files.

I noticed this in the side part from the ARRI link above:

Quote: [A digital projector has a higher gamma than a monitor because projected images in a dark surround need another characteristic than images viewed in a dim surround. The system transfer function resulting from using a DLP projector instead of a monitor is shown in the blue curve.]

It seems that they are saying that no compensation is needed, but when I see DLP projection here, the image do look at bit dark and lacking in shadow detail, maybe because they have so many lights on in the theatre to avoid trip and fall issues.

I would shoot a 18% gray card under the lighting you are using, and check that it does not read too low in the graded frames, if you convert the graded frames to BMP you should read 18% gray as about 0.458 to 0.462 or RGB= 116 to 118 or so on the 0 to 255 scale. The shareware program IRFANVIEW has a readout if you put the cursor on a spot on the image and click the mouse button it then reads out the R= G= B= value for that pixel,

http://www.irfanview.com/

If you are near midtone then it should not matter so much what gamma your viewing monitor is at, the pixel value is a better way to tell because the monitor brightness and contrast change the way the image looks anyway, you would hope the DCP projector is setup right in the theatre...

[kito]

Hi Dan,

what a flashest respons from you.
one day, if i got in CA, i will call you and hook up in the bar, guess i owed you a lot of beers, buddy.

thanks you very much Dan, and have a good day - take care wherever you are
about this case, i 'll hook 'em up at the cinema, in the morning, maybe on tuesday.
I'll let you know the result asap. and some pics preview.

God Bless You, Dan

kito
Vfx Supervisor/artist | Senior Compositor | DI artist

[Nick Shaw]

that makes the question, why do they want the monitor at 2.4 and the encoding at 1/2.22

The reasoning behind a system gamma (input transform and output transform concatenated) that is not 1 is well explained by Pointon in the PDF Stacey linked to (thanks for that Stacey. I had not read that one.)

[kito]

hi Nick , i like the way your demoing STORM
nice to meet you, Nick

cheers
kito
Vfx Supervisor/artist | Senior Compositor | DI artist

[Evangelos Achillopoulos]

What we usually do is to Grade for Filmout and then we use conversion LUT's to export for DCP XYZ or P3 etc...

More info here http://www.motionfx.gr/workflows-lut.html

[Martín Elías Iglesias]

What we usually do is to Grade for Filmout and then we use conversion LUT's to export for DCP XYZ or P3 etc...

More info here http://www.motionfx.gr/workflows-lut.html

What are that conversion LUT's?

[Daniel Esperanssa]

Just digged into my archives:

XYZ 2.6 gamma

The Digital Cinema specifications are often referring to a 2.6 gamma. When applied to XYZ
coordinates, this gamma has nothing to do with a “reproduction” gamma or with the 2.5
gamma of the CRT monitor (primed capital letters – X’Y’Z’ – are used to designate gamma
corrected values).
This 2.6 gamma is an encoding scheme which purpose is to embed in a limited digital space of 12 bits the maximum possible levels that match the human visual sensitivity.
The human visual system is much more sensible to small variations in dark areas. At the other end of the scale, large brightness variations are not detected.
This is true for almost every human sensation and the relationship between the physical magnitudes of stimuli and the perceived intensity of the stimuli.
This is sometimes called the Weber Fechner law, which is based on the logarithm function. It has been superseded today by Stephen’s power law.
Extensive tests conducted by the DCI have shown that the visual system sensitivity, in the viewing conditions of a cinema projection, is following more or less a power law with a 2.6 gamma.
The result is that:
Coding luminance values with a 1/2.6 power law allows a good balance in the number of codes representing low and high brightness values. This is the most efficient coding for transmitting the luminance details that satisfy reproduction on a cinema screen.
The 2.6 gamma, applied to the XYZ, found in the Digital Cinema equations is a coding gamma and has nothing to do with the reproduction gamma.

From Doremi "Gamma for Digital Cinema"