Author Topic: HOW TO: Make a Calibrated Material Scene  (Read 21534 times)

2017-10-06, 02:05:35

dubcat

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If you are new to CG, stuff like reflectance / albedo / sRGB (Gamma 2.2) / RGB (Gamma 1.0 / Linear) can be confusing.
In this post we will try to demystify these therms and show you how make a calibrated material scene.

There are two approaches to get the same end result.
# Use a fixed light intensity and adjust the camera exposure.
# Use 0 EV camera settings and adjust the light intensity.

We will use the second approach, because it's more practical. We can swap HDRI maps and nothing will break.

--= Sphere =--

We need a sphere to calibrate our scene.

Make a 100x100x100cm box, scans are usually 1m.



Apply a TurboSmooth modifier and use a high Iteration amount, I used 6 here.



Apply a Spherify modifier



The sphere has shrunk to 83.966cm, if you used the same settings as me.
To correct this, open the scale tool and input 119.096 into the "Offset:World %" box.
The sphere is now back to 100cm



The sphere is now hovering about 9cm above the pivot point.
This step is not essential, but stuff like this is really irritating!
Select our sphere, right click somewhere in the scene and click "Convert to:" > "Convert to Editable Poly"



Click on this wrench icon "Utility"
Click on "MAXScript"
Paste this code into the editor

Code: [Select]
for i in $ do(
i.pivot = [i.center.x,i.center.y,i.min.z]
)



Now CTRL + A the code, and drag it onto your Toolbar to make a Macro Button.
Select your sphere and click the macro button.
The pivot point should now be in the center of the sphere at the bottom.

Open the Move Transform tool and reset everything to 0,0,0.



--= 18% Gray Material =--

Gray cards are usually 18% reflectance. ColorChecker Passport "Neutral 5" is around 19.7%.
You might think, 18% what ? RGB ? sRGB ?

We are talking about 18% linear/RGB.
Create a "Corona Color" map



Click on the color preview to open "Corona Color Picker"
Uncheck "sRGB" and go into the "0-100%" tab.
Input 18, 18, 18 here and click "OK".
Do not input 18 into "Value", for whatever reason "Value" is always sRGB.



If people are talking about 90% white, they are talking about 90% linear/RGB.
Here is an overview of the average ColorChecker Passport swatches.



When you are capturing textures in real life, try to get "Neutral 5" as close to 122 sRGB as possible in camera (tethering is a huge help here). And then adjust your photo to match 100% in post.
I've noticed that on lower/medium end DSLRs you will get a better result by shooting for "Neutral 8", that is 201 sRGB.

Create a "CoronaMtl" and hook our 18% gray map into "diffuse color".
Leave Reflection at 0 while we calibrate.
Apply the material to our sphere



--= Render Settings =--

I usually use "Image Aspect" of 1.0, but do whatever you want.



Go into Performance
Set "Secondary solver:" to "Path Tracing"



I usually enable these render elements, but do whatever you want.



--= Calibrating Our HDRi =--

I will use "Apartment Livingroom 2015 – Interior" from mastering cgi in this example, because everyone and their mom has this HDRi.

Hit 8 on your keyboard and drag the HDRi into "Environment Map", this will auto change the mapping of the HDRi to "Spherical Environment".
3dsMax projects HDRi maps from the outside, this will flip our map. We have to counter this with -1 U Tiling. I wish Corona could auto apply this like "Spherical Environment".
Set Blur to 0.01



Hit "U" to go into "Orthographic" view.
Select your sphere in the view port and hit Z, this will lock your camera to the center of the sphere.
You can now hold ALT and middle mouse button to rotate around the sphere.

Fire up Interactive Render
Inside the VFB set "Saturation" to -1. We want even RGB values.
Our goal is to align the camera to the brightest spot in our HDRi. In my case that is the window above the sofa.
Rotate around and right click in the center of the sphere until you find the highest "Tonemapped sRGB" value in the center of the sphere.



18% gray is 0.459 sRGB float / 117 sRGB. We need to calibrate our HDRi until the brightest spot on our sphere is 0.459 sRGB float / 117 sRGB.
Go back into the HDRi map and adjust the "RGB Level" until the brightest value is 0.459 sRGB float / 117 sRGB.
I usually make a desaturated version of the HDRi to remove all color cast, then I plug the colored HDRi into "Environment overrides".





Calibrated HDRi



It's time to hit P to go back into Perspective mode.
Set "Saturation" back to 0 in the VFB.

Hide the sphere and import a real model. A little tip, always create materials on the actual object it's meant for, and not on a fancy shader ball!

--= Notes =--

Materials with proper ColorChecker values will look very flat and boring. This is how it should look.
Linear raw photos are just as boring.

You can toggle one of my photographic LUTs to see how the material will look in a final render.

3% black sphere with photographic LUT enabled


These are the official ColorCehcker Passport sRGB values.
If you capture your textures with a properly lit Checker and use this scene. Your materials will stay consistent and correct.

« Last Edit: 2017-10-13, 05:34:48 by dubcat »
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2017-10-06, 10:44:15
Reply #1

Fluss

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Awesome stuff as always! Thank you for sharing your knowledge! 👍

2017-10-06, 12:11:20
Reply #2

johan belmans

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2017-10-06, 13:24:04
Reply #3

nkilar

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Dude, you are something else... Thanks! :)

2017-10-06, 13:57:33
Reply #4

Juraj Talcik

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Straight into PBR Bible :- )
talcikdemovicova.com  Website and blog
be.net/jurajtalcik   Our studio Behance portfolio
Instagram   Our studio Instagram, managed by Veronika

2017-10-09, 09:33:22
Reply #5

srikken

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Super, Thank you!



The ColorCehcker Passport, would it be better to just use it as a bitmap or make an individual material for each color and model a simple ColorCehcker Passport?

2017-10-09, 13:22:33
Reply #6

Alexp

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18% grey or 13%?

I found a nice document to explain the difereces. In perfect spanish. And Im a bit confused.
https://blog.foto24.com/carta-gris-que-es-como-usarla-exponer-correctamente/#

2017-10-09, 13:55:01
Reply #7

burnin

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^ Google Translation to English > Gray card: what it is and how to use it to expose correctly

Confused about?
18, 13 or 12% - Is your choice, as you see it acceptable...

Quote
This value each photographer must decide whether it is acceptable or not.
« Last Edit: 2017-10-09, 14:02:01 by burnin »

2017-10-09, 13:59:58
Reply #8

Alexp

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^ Google Translation to English > Gray card: what it is and how to use it to expose correctly

Confused about?
It's your choice, as you see it acceptable...

If we need to take reference from 18% grey or 13%

2017-10-09, 14:04:10
Reply #9

burnin

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Updated the previous post.

Personally, i always deviate a bit... it's a personal style, preference.
As long as you know what you're doing.
;)

2017-10-10, 13:02:46
Reply #10

dubcat

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Hey guys

The important thing is to have a properly lit color reference next to whatever you want to capture. Capture the color reference as close as possible to the specified value. Adjust the raw image in post until the values match 100% to the specified value.

Once you have calibrated your HDRi inside Corona. It doesn't matter what diffuse color the sphere has, because the sphere will always be correct. If you change the color from 18% to 90%. The brightest part of the sphere should be 243 sRGB in VFB.

Since we are using 0 glossiness the white will dim a little. I'll remove the reflection/glossiness part from the main post later, so it dosn't add any confusion.
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2017-10-12, 16:58:43
Reply #11

romullus

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Materials with proper ColorChecker values will look very flat and boring. This is how it should look.
Linear raw photos are just as boring.

You can toggle one of my photographic LUTs to see how the material will look in a final render.

So should i do authoring of materials without tonemapping and only occasionaly turn tonemapping on, to see how final result will look? Also, the thing is that whenever i use one of your photographic luts, i feel that i always need to turn down exposure by 2/3-1 stop. Normally that isn't a problem, because i turn lut on, turn exposure down and continue working on other settings, but if i'd have to constantly fiddle with lut and exposure settings just to check how material will look with proper tonemapping, that would be very tedious. Or maybe i completely misunderstood workflow?
I'm not Corona Team member. Everything i say, is my personal opinion only.

2017-10-12, 19:58:17
Reply #12

dubcat

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Or maybe i completely misunderstood workflow?

Hey man!

You are spot on. The main objective is to calibrate the light source, so you know the brightest part on the object is the actual albedo.

Like you said, you have to be in full linear default mode to see the real values, but use tone mapping and LUTs to see the final result. I usually save both settings and just hit load in VFB.
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2017-10-12, 20:10:35
Reply #13

romullus

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Save/load might be good idea, i'll give it a try. Thanks!
I'm not Corona Team member. Everything i say, is my personal opinion only.

2017-10-13, 16:07:07
Reply #14

johan belmans

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Hi Dubcat,

Can you explain me why it is important to desaturate the HDRI with a color correction node together with desaturating the VFB.
Because to me it seems illogical too desaturate twice.
Although I noticed you get different sRGB values.

2017-10-13, 16:39:58
Reply #15

arqrenderz

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Me and my mom doesn´t  have that hdri :( were can we find it??


2017-10-13, 20:24:07
Reply #17

dubcat

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Can you explain me why it is important to desaturate the HDRI with a color correction node together with desaturating the VFB.

It's just in case people don't desaturate the HDRi :)
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2017-10-26, 08:57:26
Reply #18

James Vella

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Thanks Dubcat, this made a big difference to some of the balancing issues I was having!

2017-10-29, 03:52:03
Reply #19

shortcirkuit

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so correct me if I am wrong, this exercise is to get the lighting vs albedo on textures correct?   By putting the DE SATURATED HDRI in the environment slot, the grey 18% will be consistent across the scene and all colors should be quiet accurate.  You must also used the normal HDRI in color and put them in all of the overrides (reflection, refraction + direct visibility).  Correct?

Also, in terms of the process, the way i understood is to put the sphere in the middle of the rendering viewport and ensure the brightest part (lets assume a sunny exterior HDRI from peter guthrie) is right in the middle of the sphere.  SO if you were to change the grey 18% material temporarily to a CHROME reflective ball, the sun should be right in the centre of it and that is where you sample your values from (but ensuring you change it back to grey 18% of course).
Is this all correct?

Thanks

2017-10-31, 15:39:48
Reply #20

dubcat

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Hey

Quote
Correct?

Spot on.

Quote
temporarily to a CHROME reflective ball

Smart idea!

Quote
Is this all correct?

Yes.
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2017-10-31, 23:39:52
Reply #21

shortcirkuit

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awesome thanks for clarifying - very much appreciate your efforts and knowledge mate!

2017-11-24, 20:13:48
Reply #22

dj_buckley

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I genuinely don't get the point of this?  Can someone explain why you would do this?

I keep seeing 'turn on a LUT' to see the final rendering.  Isn't whatever is in the frame buffer the final rendering?

I am having an issue with images generally looking quite flat in Corona frame buffer, maybe this is what I'm missing?

Apologies for the basic level of understanding

2017-11-24, 23:16:08
Reply #23

dubcat

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When we use real world albedo values stuff will look flat. Real camera raw files look just as flat. So we have to enable a LUT or crank the contrast slider to get a processed image look :)
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2017-11-25, 00:15:21
Reply #24

dj_buckley

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Makes sense, i think i’ve been using a mix of albedo maps and standard textures which could be the cause of my headaches.  I guess as soon as you go down the albedo route, all your textures/colours need to be in line, otherwise you’ll have some very oddresults as i did recently

2017-11-25, 00:23:15
Reply #25

dubcat

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Here is a Photoshop script I made to convert non albedo maps over to albedo. It uses "Apply Image" to make a 1:1 split, and the "highpass" layer keep all the hue variation. You just have to change the albedo color to a proper color, and maybe reduce the contrast on the highpass layer, if the original map is way off.

I use this method all the time to fix old foliage to megascans.

You can do this in corona too, like this.
This should be an official corona map if you ask me! It's so good on glossiness maps.

« Last Edit: 2017-11-25, 01:58:34 by dubcat »
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2017-11-25, 16:28:47
Reply #26

dj_buckley

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Ok, so that just leaves me to ask - what's the point in all of this?  Is it purely to suit other workflows?

It seems to me that all we're ultimately doing is removing contrast, just to add it back in?  Take a nice contrasty texture, flatten it, render it, add contrast back in using the frame buffer?

What have we been doing up until this point?

Also I have another question regarding the frame buffer, was/is VFB the same as CFB, I never seemed to have to as much 'post work' in the frame buffer with VRAY to get a nicer looking result, but that could be because I was using textures that i'd already edited to look good in the frame buffer.

It just feels like a bit of a convoluted workflow just to aid the pursuit of 'physical correction' something the end client probably isn't going to notice or appreciate right?

2017-11-25, 19:51:25
Reply #27

Juraj Talcik

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Are you commenting on the last post purely ?

That doesn't concern contrast outside of correction if needed. It gives you the flexibility to real-time adjust albedo(color) of any texture. Highpassing separates "Color" and "Detail" into two separate parts. I do this in Photoshop, with map like above, it could be done automatically.

Regarding Corona buffer and Vray buffer, yes, they are very much identical. Their tonemapping are actually exact copies of basic Reinhard just with different control (Vray inverted/remapped 1-99 into 0-1 range).
Both renderers benefit (or require) the same kind of post-production for different look.

If you are satisfied with how your renders look in framebuffer than I don't see what is your problem with.
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2017-11-25, 23:47:34
Reply #28

dj_buckley

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No apologies - i was querying the use of These flat Albedo textures in general as opposed to just using internet/camera sourced diffuse maps as we have done for years.

What’s the end goal? Ultimate control?  To get as true a raw image as possible when compared to how a camera/our eyes work?

I just wrapping my head round the whole PBR thing

2017-11-26, 08:07:27
Reply #29

James Vella

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Correct me if Im wrong, I have been following this with great interest and as for my understanding dj_buckley, the point is to have a color managed workflow. For example - if you have followed the above and calibrated your HDRI correctly, then straight into the frame buffer your Dulux colours should match 1:1 in the lit areas of your scene (I certainly get asked repeatedly by clients is this the EXACT hue/value, it looks about 5% darker than it should be?). Since following this I have had to do no additional post work to correct for this slight difference.

Im still wrapping my head around this part (separating the albedo) but Im guessing it ties into the first part of this tutorial, you can then place the exact colour of timber (in this case) on your boards that your client has requested and know that its going to be the exact colour they have requested. You are then free to use the textures you always have however change the colour on the fly, I can already think of other instances where this would be useful but just that alone is enough to sell me on the idea - not to mention I love workflows that incrementally make my life a lot easier.

Thanks again dubcat, your constant research has inspired me to keep digging and learning the finer parts of what I have ignored in the past due to my ignorance of - "well it looks pretty close" and then working my ass off on that last 5% in post anyway.
« Last Edit: 2017-11-26, 09:26:43 by James Vella »

2017-11-26, 09:43:19
Reply #30

dj_buckley

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Yep - thanks James, I should probably have started another thread, questioning the use of Albedo over normal diffuse maps rather than confuse it with the original post - which I get.

I'd get so frustrated being told by manufacturers things were wrong when their own product would look wildly different when held under different lighting conditions

2017-11-26, 09:47:01
Reply #31

James Vella

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I'd get so frustrated being told by manufacturers things were wrong when their own product would look wildly different when held under different lighting conditions

Hah, I know right! This method solved most of those issues once I calibrate each HDRI and keep them desaturated for lighting purposes, however I still have to explain to them in shadow areas it will appear darker (duh!)

Dubcat, I have setup the material as you have above and it come out completely white - until I unchecked "Perform mixing in sRGB space" on all the CoronaMix Texmaps - is this correct?
Also, is the last operation "Dynamic Texture" in overlay mode?

Cheers

Edit:
This is when I set up the material as you have it with "Perform mixing in sRGB space" switched off - which made the blacks too milky


I adjusted the second last node "Compiled" with a gamma of 0.45 which brought back all value as I would expect


Then I switched "Perform mixing in sRGB space" back on for the CoronaMix nodes, and removed the Gamma 2.2 (since a 0.45 at the end is reversing this anyway) and I got closer to what I was looking for... Do we really need to add the Gamma in and then remove it or can we take that step out as I have below? Or did I miss something here


If thats the case, could we simplify it once more to something like this?


edit: My blacks are not even close, Im definitely missing something here

« Last Edit: 2017-11-26, 10:39:25 by James Vella »

2017-11-26, 11:03:53
Reply #32

romullus

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Guys, can we at least settle down on terminology? I get impression, that some are talking about albedo as texture map with removed ambient shadowing and others treat it as colour separated from details component. It's so darn confusing...

Anyways, huge thanks to dubcat for his invaluable effort!
I'm not Corona Team member. Everything i say, is my personal opinion only.

2017-11-26, 11:13:35
Reply #33

dj_buckley

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Probably the reason I'm so confused

2017-12-01, 16:23:50
Reply #34

dubcat

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Hey guys, been afk from the forums this week.

the point is to have a color managed workflow.

This pretty much answers all the questions.

is this correct?

Have you tried to render the material ? The material preview has some kind of bug, I reported it on mantis a week ago or so.
Add and Divide has to be done in linear.

It's so darn confusing

The original post is about calibrating you HDRis, so the brightest part of the sphere is the actual albedo color.

The texture splitting stuff is irrelevant to the original post, it's about taking control over the actual texture albedo.
I use it all the time for glossiness too, you keep all the details but you can change the glossiness value, so good.
« Last Edit: 2017-12-01, 16:33:36 by dubcat »
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2017-12-02, 20:40:29
Reply #35

James Vella

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Ok Brilliant, so that must mean the last node (Dynamic Texture) is on Multiply mode - correct?

Thanks!

2017-12-07, 19:51:20
Reply #36

dubcat

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Ahh sorry I didn't tag the last one. It's "Linear Light" :)
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2018-03-18, 16:16:52
Reply #37

joeperry54

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Thank you!
« Last Edit: 2018-03-20, 00:45:55 by joeperry54 »

2018-11-12, 00:46:15
Reply #38

amrelshipli

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Awesome ! u are genius ! can u upload the hdri plz ! i cannot find it anywhere plz !

2018-11-18, 23:29:06
Reply #39

Xntric

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I'm in the process of making a shaderball scene for Lookdev.
And I want the scene to be lit up by HDRI.

I think that when you're creating and testing new shaders, it's important that you do it in a properly white balanced and colour-calibrated scene, or am I wrong?

I have followed the guide in this thread and adjusted the hdri to match 18% grey.

So far so good.
My question is, should I also use a colour checker and adjust the hdri to match that?
And if so, how would I do that?

2019-01-15, 02:43:13
Reply #40

springate

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Does the Exposure Control rollout (shortcut 8) make any difference using this process? Should i set it at "no exposure control"?

2019-01-24, 02:16:04
Reply #41

dubcat

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Awesome ! u are genius ! can u upload the hdri plz ! i cannot find it anywhere plz !

https://gumroad.com/jorgenhdri

My question is, should I also use a colour checker and adjust the hdri to match that?

You should use that HDRi as a HDRi. And then go into the Corona settings and switch from EV to Camera settings, and input the same ISO, Shutter and Aperture values you used when you captured one of you photos. Create a Linear profile for you Camera with 3DLUTCreator. Open your photo in Lightroom and apply the linear camera profile. Save it as sRGB 16 Tif, and open it in Photoshop. Recompile your HDRi with the linear tifs.. Sample a place in your linear photo, and adjust the values of your HDRi with a color correction to match this value, while you have the proper corona camera settings.

Does the Exposure Control rollout (shortcut 8) make any difference using this process? Should i set it at "no exposure control"?

I never use Physical Camera, because it gets affected by the tonemapper in "8". Use Corona Camera and its camera settings instead.
« Last Edit: 2019-01-24, 03:03:28 by dubcat »
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2019-04-11, 07:50:38
Reply #42

cjwidd

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Firstly, thank you *so* much for this post, it is tremendously helpful. Second, in Corona version: 4 (DailyBuild Feb 18 2019) the color picker in the Corona Color texmap does not show options for sRGB, 0-255, 0-1, 0-100 are not visible.

- Has this [very useful] feature been removed or can it be enabled elsewhere in the UI?

You calibrated neutral gray as 18% linear/RGB, which is something like 117, 117, 117 sRGB.

- How does 128, 128, 128 compare to these values? Is 128, 128, 128 not a neutral grey?

Regarding ColorChecker Passport swatches. In the far right of the image (p.1), black is indicated as 3.1% linear/RGB. In another post I have seen black calibrated differently, e.g. "artistic" [30-240] sRGB; "strict" [50-240] sRGB.

- How does one make sense of these different interpretations in terms of best practices?

« Last Edit: 2019-04-11, 09:02:13 by cjwidd »

2019-04-11, 10:18:19
Reply #43

romullus

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Firstly, thank you *so* much for this post, it is tremendously helpful. Second, in Corona version: 4 (DailyBuild Feb 18 2019) the color picker in the Corona Color texmap does not show options for sRGB, 0-255, 0-1, 0-100 are not visible.

- Has this [very useful] feature been removed or can it be enabled elsewhere in the UI?

No, it hasn't been removed, but you have to enabled it first. Go to customize>preferences>general and choose color selector -> Corona improved picker.

Regarding ColorChecker Passport swatches. In the far right of the image (p.1), black is indicated as 3.1% linear/RGB. In another post I have seen black calibrated differently, e.g. "artistic" [30-240] sRGB; "strict" [50-240] sRGB.


- How does one make sense of these different interpretations in terms of best practices

3.1% RGB <-> 8 8 8 RGB <-> 53 53 53 sRGB As you can see there isn't different interpretations here.
I'm not Corona Team member. Everything i say, is my personal opinion only.

2019-04-11, 10:47:27
Reply #44

cjwidd

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Ah, yes, the Corona Improved Picker makes interpreting the different values *much* easier, thank you for pointing that out.

You are correct, there is not a difference of interpretation, which I can see now thanks to the Corona Improved Picker.

My only other question pertains the sRGB 128, 128, 128 "grey". I had some naive opinion that sRGB 128, 128, 128 is somehow neutral grey, although I cannot account for where / how I acquired that opinion; perhaps because 128 is in between 0-255.

Nevertheless, the point is that sRGB 128, 128, 128 color is not of any particular import as it pertains to calibrating exposure, correct? I apologize if these questions are offensively basic, but I just want to be clear about the interpretation of RGB and sRGB going forward.

2019-05-12, 23:24:46
Reply #45

claudyo

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I use it all the time for glossiness too, you keep all the details but you can change the glossiness value, so good.

Hi Dubcat,

What did you mean by this? I've tried that method and indeed does a really good job at taking control over albedo, but after I've read this I've got confused about generating glossiness from it. Do you care to explain a bit?

Ta