LUTS QUESTION

[lou4uandme]

Hello,
Very strange findings...
I created a test pattern chart in photoshop. It had 10 vertical bars with rgb values 0, 4, 17 ,28, etc.

I sampled the "4" bar and nuke correctly showed "4" (using 8 bit scale)
Ok here is where it gets strange,

When I changed the read node to "raw Data" or "linear" and set the viewer to "none" the values increased.
4 became 34, 17 became 73, 28 became 93, etc..
How could this be? How are the images values increasing if the luts are not suppose to effect the image values?

Thanks,
Lou

[mr_tsoi]

Hello,
Very strange findings...
I created a test pattern chart in photoshop. It had 10 vertical bars with rgb values 0, 4, 17 ,28, etc.

I sampled the "4" bar and nuke correctly showed "4" (using 8 bit scale)
Ok here is where it gets strange,

When I changed the read node to "raw Data" or "linear" and set the viewer to "none" the values increased.
4 became 34, 17 became 73, 28 became 93, etc..
How could this be? How are the images values increasing if the luts are not suppose to effect the image values?

Thanks,
Lou

http://thefoundry.co.uk/pkg_examples...E-C198B0171453

download 4 parts of color menegment. There is quit clear description

[lou4uandme]

Ok, I think color M 03 explains more, CM04 seems to be workflow examples.
Although he explains how the viewer & read nodes display different color shades, He doesn't show why the "values" change.
Also, I thought the "LUTS" are not suppose to change the rgb values of the image, it's just for viewing purposes.

What am I misssing?

I thought that if you create an image in photoshop with a rgb vaule of 60, and then add it to nuke, the rgb value should still be 60. It is, if I set it to sRGB to both. However, If I choose to bypass the IP, and set it to "raw & none, although it looks correct, that 60 rgb value is much higher.
Why is that? Why, why why??? ahrrr... my mind is overloading...!!

[radders]

The read node will change values becasue it has to take the image and convert it from whatever colour space it is in into linear colour space. Most images have a LUT baked in when they are saved and Nuke applies the inverse to get it back to a linear space.

When you set the LUT in the read node you are telling Nuke what colour space the source image has been saved in. If you leave it set to default Nuke will guess, depending on the file type.

The viewer LUT should not change the values, just how they are displayed.

[lou4uandme]

AH, I see.
I thought that "raw" or Linear, did nothing to the image.
That's why I'm so confused, I'm thinking if I bring in an image and select Raw or Linear, nuke would not change any values .
when I see that the only way I get the correct values is to select sRGB, I get confused.
Thanks again.
lou

[schmoby]

I think it's because Nuke auto-detects what you're loading. Load a JPG and Nuke will apply a gamma to it right away. If you then change it to 'linear' you'll see it change again.

[lou4uandme]

Yeah, sometimes I think it's better for me not to think too much..
But when I see things that I can't explain, it haunts the crap out of me. (LOL)
For example, look at my post http://www.vfxtalk.com/forum/day-4-n...ma-t23641.html
A clear example of my mind in overdrive.