Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: astudio on 2016-11-12, 17:03:07
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Please in simple words if possible.
There is no glossy in my test. IOR=1
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Umm, sorry, but can you explain what is this?
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Left and right corona color wit RGB 0,0,0 and 43,43,43
Middle bitmap with same values
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Are you asking why you need anything other than black to dark grey for the diffuse channel?
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There is a lot of tutorials that we need to use albedo in this range 43-240. Why?
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Because that's the range observed empirically in real life. Coal is regarded as the darkest (common) material on earth and has a approx measured albedo value of 43. Snow is regarded as the brightest and has an approx measured albedo value of 243 (sRGB). Even if today, we have made some spectacular materials like the well-named Vantablack.
Edit : For the curious : http://petapixel.com/2016/03/07/the-darkest-material-on-earth-is-now-even-darker-than-before/
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It's right usually for common materials. But I need now black paint with LRV 6%. So I need RGB 15,15,15. Is it OK in terms of PBR? Because 43,43,43 is just grey near it.
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Be carefull, [43,240] is the sRGB range which translates into [8,230] RGB.
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I know. And this things confuse me.
I made bitmap for my test in photoshop (it means sRGB) and load it into diffuse as automatic. (it means gamma 2.2) .
And for another cubes I used CoronaColor instead of diffuse color.
So I really tested sRGB value, isn't it?
My question is: Is it possible that in my case CoronaColor 15,15,15 would be physically correct?
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yes, with "Input values are in linear color space" checkbox checked. Which translates into [70,70,70] sRGB.
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No. I input a hex color here, wich I take in photoshop picker.
I see in bottom color rectangle sRGB 43,43,43.
Is a reason for 43 just color of charcoal or there is any mathematics reason?
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@astudio: have you seen this: https://forum.corona-renderer.com/index.php/topic,13833.0.html
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Yes, I read. And install Corona picker. So I sure that I use sRGB.
Offtopic. As I understand hex number of color is a function of color model, not color space. When I put hex number, "insert value in RGB" checkbox is not active, and you see real sRGB value in the bottom rectangle.
By same reason for calibrating albedo value I check lightness value in Photoshop in Lab mode. You deal with color model, not color space, so you don't need to think about RGB-sRGB. You free from hue and saturation.
To the thread. Is it ok to use color darker then 43,43,43 sRGB or there are some mathematical restriction? Or may be a range 43-240 is RGB range and not sRGB?
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OK now i see what you try to acheive. You confuse Lightness from Lab color space and LRV (Light reflectance value). LAB is a way to describe colors and LRV is a measure of light that is reflected from a surface when illuminated by a light source. So 4% LRV does not mean you have to put 4% lightness in LAB color space and get the corresponding sRGB value. That's not the way it works. You can see this link, from a coating manufacturer, where you can find some LRV - RGB correspondence (They say RGB but i assume it is sRGB in reality) :
http://www.duluxpowdercoatings.co.nz/wp/wp-content/uploads/2013/11/Copy-of-RGB-References2.pdf
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I don't try to connect LRV and Lab of course. There are two different things, as green and warm.
I use Lab when I need to use known albedo value from reference book. Unfortunately there is not a lot of information :(
For example I know that albedo(sRGB) of red brick is 148. In this case I guess that I need adjust my texture in Lab mode till I get lightness 148. If I work in RGB mode (sRGB of course), all parameters are depending. You may change luminosity in 3 ways by changing hue, saturation and lightness. It always confuse me lightness, brightness, luminosity :). In Lab mode there is only one way.
I don't know what does it mean Albedo (sRGB) = 148 and why they give monochrome information. But I guess that green or blue bricks will have same lightness in Lab mode. Correct me if I wrong. In RGB mode lightness depends from color.
EDIT: Tests show that something wrong in this workflow. I don't delete it from here. Show me please my mistake. Have you an idea how to use monochrome albedo (sRGB) Values?
In my particular case I guess that paint is black and if LRV is low - I need low glossy, low IOR material. (IOR is another long story for another thread which I'll open for sure after understanding albedo). But the question is how much black. With low LRV I can imagine that it is darker then charcoal. So my question is if we have some restrictions to use RGB less then 43?
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I too would like come clarification on the subject. It's not too long ago since BBB3 and others convinced (or rather shed information to their own workflow) that you shouldn't go over RGB range 160-180 for white and this new method skyrockets way above this.
And yes the new suggested dark coal material looks washed out at default so I guess it's a matter of lowering ISO to get the whites to an accectable range, while at the same time the new proposed max blackish value of RGB 43,43,43 would in turn actually look pretty black? I haven't had the time to test this yet but I'm super critical about the whole idea so please if anyone has done any actual tests even with an empty room (but a closed space nevertheless so the light just doesn't bounce in to space the first second) sized with the to extreme values in form of white walls and blacks repsesened with teapot/boxes or realt furniture to show how shadows look and having it look like natural white and black values without Photoshop post processing I would be eager to see your results.
This is a confusing area because the rules seem to change every too years. And to follow up with a closing question, if I have wall painted with a really white paint, say RGB 210, with the light bouncin' around more and the "new black" being RGB 43, wouldn't this kill all the contrast from shadows because of the significantly whiter diffuse/albedo, thus light bouncing way too must in the corners and other shadowed aras? Just a straight up question to which I'm hoping the solution is not to increase contrast in Photoshop since that is not the way I need to manipulate my images when shooting with a DSLR camera.
I hope I made myself clear, just woke up and had me first coffee :)
Thanks if anyone could shed more info on this!
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well you should read this : http://viscorbel.com/vray-materials-part-1-diffuse/
By using real world values, you know that light bounces and energy behave like in real world. What you obtain in the end can be regarded as a RAW image taken with a DSLR. When you first look at it, it looks dull but once graded it looks like what you are used to :
https://www.slrlounge.com/wp-content/uploads/2010/10/03-raw-vs-jpeg-contrast-blacks-brightness.jpg
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Thank you
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well you should read this : http://viscorbel.com/vray-materials-part-1-diffuse/
By using real world values, you know that light bounces and energy behave like in real world. What you obtain in the end can be regarded as a RAW image taken with a DSLR. When you first look at it, it looks dull but once graded it looks like what you are used to :
https://www.slrlounge.com/wp-content/uploads/2010/10/03-raw-vs-jpeg-contrast-blacks-brightness.jpg
Thanks for the link, I've read it before but I'll give it more tought his time around. I'm still doubtful because I've been around long enough to see the "correct" workflow been found time and time again, until the next wave comes around :D But yes at the end of the day I want energy behavior like in the real world, so it's worth a shot if it gets the contrast between light and shadow more correct.