Color temparatures, sky color, ect. and COLOR SPACE

[pailhead]

Vlado? ....

[vlado]

Yes...?

Best regards,
Vlado

[pailhead]

Well, can you read my first post and give an opinion? When working with kelvins, the results tend to differ greatly.

[vlado]

In general, light colors should not be gamma corrected. This is because they are derived from physical observations or formulas - they do not start as user-input colors. The IES Kelvin color is derived from Plank's formula for the spectrum of black body radiation. The color of the sun is based on a table of the observed and measured illuminance spectrum of the sun. There is no gamma involved anywhere in this process.

Note however, that when using the IES lights or the sun/sky, it is recommended to use the VRayPhysicalCamera with the white balance set to D65 standard CIE illuminant - otherwise, the colors might tend to be too much on the blueish side.

Best regards,
Vlado

[pailhead]

But how am i supposed to use them in a gamma corrected workflow?

These are obviously different temperatures, one is much colder than the other, or one has more kelvins than the other.

But they are the same light, with the same amount of kelvins. This is where i get confused.





Note: The issue would be obvious with warm colors as well...

[vlado]

Hmm, maybe I don't understand something correctly here. The Kelvin temperature defines what light spectrum is emitted by a light source, not how warm or cold this light looks to you. It is an absolute measure rather than a subjective one. On the other hand, the "warmth" or "coldness" of colors is purely a subjective term without a particular physical meaning. Green is a warm color, but there is no blackbody spectrum for it (there is no Kelvin value that will produce green).

If you have a bulb that emits light at approximately 3200 Kelvin spectrum, you can take many different photos of this light, with different white balance settings - each of them will produce an image with different color tint, but that does not mean that the light source has somehow changed.

Best regards,
Vlado

[pailhead]

I was under the impression that all of the professionals who have anything to do with Kelvins refer to light as either warm or cold. Lower temperatures are referred to as warm, (red/orange/yellow) while higher temperatures are referred to as cold (blue).




Let me ask you this:


I notice that the color switcher changes depending on how many kelvins i choose. The color seen in the switcher corresponds to what the IES emits in a gamma uncorrected render. So, when i choose 8000K i get a blue, cold color. If i tick of the temperature parameter, i can actually read the color in RGB.


The bottom line is, gamma/LUT settings screw up everything, but while i can bring everything back by applying inverse gamma, vray sky and IES are out of reach.



How does this relate to the blackbody theory?


Take a look at the first to images in my post above (ones without GI), if i were to put a yellow filter on my lense in real life, the deep blue would shift towards neutral, but the neutral one would actually shift to a warm color.

[pailhead]

If you have a bulb that emits light at approximately 3200 Kelvin spectrum, you can take many different photos of this light, with different white balance settings - each of them will produce an image with different color tint, but that does not mean that the light source has somehow changed.

But i am not using any white balance settings. Even if i did, the problem would remain. While a white balance setting would shift my tint, gamma settings would still wash it out.

[vlado]

Yep, washing out is what gamma does - under the presumption that your monitor is calibrated and will revert this back to the original image when it is displayed.

Best regards,
Vlado

[victor.nsy]

From my understanding most photograph are taken with setting that is asthetically pleasing
to the eye. Setting that emulate moods or add to the atmosphere. Every little tweeking and
even darkroom post processing affects an image output. In science, lights color such as
8000K may not look right when rendered off a machine becos the human eye is a very advance
equipment it corrects color. For all you know, every image looks slidely different to everyone,
every sunlite environment as well. So there is an absolute number in science - in some cases
non, or at least we can draw graphs to read behaviors -, but in art there is non.

What looks right is right afirms this believe. In art we break some rules of nature making things
looks better than they really are. Or to emulate a mood.

I would say the blueish 8000k is the correct scientific render of the actual scientific colors.
However, a human standing in that same space using his eyes (not with a camera) would
see a less blueish environment. Hope it explains that nature of our biological part are really
advance.

More to colors and how it appear to be there are many factors, your monitor calibration,
your immediate environment (seating near a window) affects colors. Viewing angle of the
screen ... . Some graphics studio have their environment made to view images with D50
controlled light environment, then you are set to talk about correct color!

[pailhead]

Yep, washing out is what gamma does - under the presumption that your monitor is calibrated and will revert this back to the original image when it is displayed.

Best regards,
Vlado

Why do i have to modify my textures and colors then? By simply applying gamma, people complain that their images are washed out. But when applying gamma to textures and colors, everything works out fine.

[pailhead]

I guess i'm the only one who is confused here.


Do you see anything different between these two images?!?







I do. One is blue, the other one is not.


Possibilities:

1. Different lights. One is 8000k, the other one is 5500k. False
2. Different lights. They're both 5500k, but one of them has a filter. False
3. Different camera settings, either a filter has been applied to the lense or the white balance changed. False

What other explanation is there, how do you explain gamma in real world?


If someone showed me two photos like this, and told me that they were shot using the same camera, same film and same lense (with or without filters), i would say that the lights were different, either had a filter applied, or were different temps.

[pailhead]

128 gray without gamma changes



128 gray with gamma changes - it's washed out




on the left, there is a washed out texture, just like the above color is washed out, but when i set the input gamma in gamma/lut settings to 2.2 as well, this is corrected, and i see the image the way its supposed to be (right)





This is pretty self-explanatory.

[pailhead]

Yep, washing out is what gamma does - under the presumption that your monitor is calibrated and will revert this back to the original image when it is displayed.

Now, i'm confused with this statement.

• Why are there gamma input options when importing a bitmap into max?
• Why does color correct plugin feature a gamma parameter?
• Why is there a gamma parameter implemented into vray color.
• Why do all of the LWF tutorials (like this one) feature a quote similar to this (after having applied the 2.2 gamma curve to an image) "Now you probably think: "this image looks flat and washed out". This is because I didn't change anything to the material. The material in the gamma corrected image is in fact much brighter compared to the material used in the first image (the material is also gamma corrected, so it gets brighter)."

[victor.nsy]

There is no correct image, a correct image only exist in the mind of the beholder.
Do what looks right to you. It is possible to create a linear environment thru knowledge.
However our world is non-linear. And even if it's possible, then everyone will produce the
same work. If your work needs to be scienfical correct then ignore how it looks becos it's
accurate, since it's set according to scientific observation.

In concept what GI does is to give you light reflecting off the surface of matter. The maths
behind it is human input (digital) to emulate nature. And nature it's has no fomulas (analog).
The good news is that we are human a part of nature, so we can observe and create
freely, not bound by digital values.

Be free, my friend have an understanding of the technology behind it is important but dont
rely on it as an artist.