1
Work in Progress/Tests / Re: iridescent shader
« on: 2020-07-01, 10:19:29 »
No I don't think it is, he is comparing two options
2025-06-20, 00:36:10
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2
Work in Progress/Tests / Re: iridescent shader
« on: 2020-06-25, 10:55:12 »
How did you achieve this effect?
3
[Max] General Discussion / Re: Correct Macbeth / X-rite Color checker albedo values in Corona
« on: 2020-06-24, 11:18:06 »
Not one reply! I even posted links to this thread in various facebook user groups...
Aside from the color checker, I would just like to know how corona is calculating the rgb > reflectance values.
In the images attached you can see the behaviour of the corona color picker.
You can see that rgb 243 is around rgb 224 in linear color space (88% reflective?), so why is that still considered too bright?
Is corona actually using the linear value internally or the sRGB value?
I ran the same test in Octane and unlike Corona, the Linear values were used so there were no problems using the color checker to calibrate the images.
I'd really love to get to the bottom of this...
Thanks!
Aside from the color checker, I would just like to know how corona is calculating the rgb > reflectance values.
In the images attached you can see the behaviour of the corona color picker.
You can see that rgb 243 is around rgb 224 in linear color space (88% reflective?), so why is that still considered too bright?
Is corona actually using the linear value internally or the sRGB value?
I ran the same test in Octane and unlike Corona, the Linear values were used so there were no problems using the color checker to calibrate the images.
I'd really love to get to the bottom of this...
Thanks!
4
[Max] General Discussion / Re: Correct Macbeth / X-rite Color checker albedo values in Corona
« on: 2020-06-18, 19:29:38 »
I had done some more tests.
Assuming again that the actual 'reflectance' values are measured in linear colour space, I have based the exposure value for the color checker on an aparrently known reflectance value of the large grey swatch (according to this article: https://www.chromaxion.com/information/ColorChecker_Passport_Technical_Report.pdf ) which has 60% reflectance. I have attached the results.
At this level of exposure the calibration result yeilds more believable reflectance values (although I still find it hard to believe that some of swatches ar actually 100% saturated)
But for this to behave accurately it would still require:
A: The color checker to calibrate the images such that any camera response curves were flattened (aside from the 2.2 gamma curve of the image format)
B: That corona also removed the SAME gamma curve of the image format before rendering in linear space.
C: And that The SAME gamma curve was re-applied in the VFB if exporting in 8 or 16 bit...
I'm still yet to find anything conclusive about color and exposure calibration of image textures for use in physically accurate render engines.
I'd really love to hear some thoughts on this.
Cheers!
Assuming again that the actual 'reflectance' values are measured in linear colour space, I have based the exposure value for the color checker on an aparrently known reflectance value of the large grey swatch (according to this article: https://www.chromaxion.com/information/ColorChecker_Passport_Technical_Report.pdf ) which has 60% reflectance. I have attached the results.
At this level of exposure the calibration result yeilds more believable reflectance values (although I still find it hard to believe that some of swatches ar actually 100% saturated)
But for this to behave accurately it would still require:
A: The color checker to calibrate the images such that any camera response curves were flattened (aside from the 2.2 gamma curve of the image format)
B: That corona also removed the SAME gamma curve of the image format before rendering in linear space.
C: And that The SAME gamma curve was re-applied in the VFB if exporting in 8 or 16 bit...
I'm still yet to find anything conclusive about color and exposure calibration of image textures for use in physically accurate render engines.
I'd really love to hear some thoughts on this.
Cheers!
5
[Max] General Discussion / Correct Macbeth / X-rite Color checker albedo values in Corona
« on: 2020-06-18, 15:34:18 »
Hi All,
I just wanted to open a discussion about something that has been bothering me for years now.
I would like to know how to accurately calibrate photographed texture maps for use in Corona, so that texture behaves physically accurately, as well as just looking correct.
I have been using a color checker to calibrate photographed textures, this works but I have always felt that the colours are maybe not true to life when looking at the rgb values (see image attatched).
The white is 243 or 95.3% reflective, which sounds far too reflective, and most of the coloured swatches are 100% saturation, which is far greater than with the default camera profile.
The following stagement: "The code value of 118 in an 8-bit system corresponds to 18% of the maximum final output for sRGB." suggests that the correct value for 'mid grey card' which reflects 18% of the light hitting it would be rgb 118,118,118, instead of rgb 46,46,46 because of the gamma curve.
I'm assuming Corona offsets the gamma curve, converting textures to linear color space before path tracing.
If this it the case, then a value of 128 in gamma 2.2 would result in rgb 47, or 18% reflectivity (sounds about right...) and a value of 243 in gamma 2.2 would result in rgb 225, or 88% reflectivity, which also sounds.. correct.
This suggests that the X-rite calibration values are in fact accurate to physical reflectance values, when converted to Linear colourspace / Gamma 1.
The question is, if this is correct, why have I been hearing for so many years from almost every source that a white value of 243 would be far too high, and that 225 should be a maximum.
It seems all the references of albedo to rgb value conversions have not been taking the gamma curve into account?
I'd really love to hear peoples thoughts on this because it is something that has never sat well with me.
I just wanted to open a discussion about something that has been bothering me for years now.
I would like to know how to accurately calibrate photographed texture maps for use in Corona, so that texture behaves physically accurately, as well as just looking correct.
I have been using a color checker to calibrate photographed textures, this works but I have always felt that the colours are maybe not true to life when looking at the rgb values (see image attatched).
The white is 243 or 95.3% reflective, which sounds far too reflective, and most of the coloured swatches are 100% saturation, which is far greater than with the default camera profile.
The following stagement: "The code value of 118 in an 8-bit system corresponds to 18% of the maximum final output for sRGB." suggests that the correct value for 'mid grey card' which reflects 18% of the light hitting it would be rgb 118,118,118, instead of rgb 46,46,46 because of the gamma curve.
I'm assuming Corona offsets the gamma curve, converting textures to linear color space before path tracing.
If this it the case, then a value of 128 in gamma 2.2 would result in rgb 47, or 18% reflectivity (sounds about right...) and a value of 243 in gamma 2.2 would result in rgb 225, or 88% reflectivity, which also sounds.. correct.
This suggests that the X-rite calibration values are in fact accurate to physical reflectance values, when converted to Linear colourspace / Gamma 1.
The question is, if this is correct, why have I been hearing for so many years from almost every source that a white value of 243 would be far too high, and that 225 should be a maximum.
It seems all the references of albedo to rgb value conversions have not been taking the gamma curve into account?
I'd really love to hear peoples thoughts on this because it is something that has never sat well with me.
6
[Max] I need help! / Re: UHD Cache settings for animation?
« on: 2015-07-09, 11:26:07 »
Thanks, I'm much clearer on that now. I'll try to upload a simplified scene where the flickering is present when I have a few minutes spare.
7
[Max] I need help! / Re: UHD Cache settings for animation?
« on: 2015-07-09, 01:25:44 »
Thanks for the advice. Yes that was the page I was referring to. The scene I was working on had some dark corners which would have required many indirect bounces to illuminate, even with precision set at 3 there was pretty bad flickering (not noise). In the end I added some other lights and the flickering cleared up.
I can see the documentation is fairly clear but I just struggled to understand exactly what 'load and try to append' was actually doing and when it should be used. If the cache is 'appended' each time what benefit do you gain over calculating from scratch each time?
If during the animation a new area is exposed (e.g moving passing a doorway into another room), would the single pre-loaded cache not fail to calculate the lighting in that area?
I would normally just run several tests but in these circumstances it can be extremely time consuming, and doesn't necessarily improve my understanding of the processes that determine the result.
Thanks again.
I can see the documentation is fairly clear but I just struggled to understand exactly what 'load and try to append' was actually doing and when it should be used. If the cache is 'appended' each time what benefit do you gain over calculating from scratch each time?
If during the animation a new area is exposed (e.g moving passing a doorway into another room), would the single pre-loaded cache not fail to calculate the lighting in that area?
I would normally just run several tests but in these circumstances it can be extremely time consuming, and doesn't necessarily improve my understanding of the processes that determine the result.
Thanks again.
8
[Max] I need help! / Re: UHD Cache settings for animation?
« on: 2015-07-07, 13:32:22 »
I just wanted to add that I have read the UHD Cache info page but don't fully understand it.
9
[Max] I need help! / UHD Cache settings for animation?
« on: 2015-07-07, 12:56:55 »
Hi,
I have a animation to render and wondered if someone could give me advise on the best uhd cache settings?
The shot is fairly simple, it's just a camera moving down a corridor with white walls either side, and a glossy concrete floor. The shot is about 200 frames long.
What would be the best approach for the HD Cache? Should I be using load and try to append? If so how would I go about this? Am I right in thinking I would render out 10th or 20th with settings: calulate from scratch - save to file, then render out every frame using settings: try to load and append - save to file?
I'm still a little confused about how try to load and append actually differs to load from file.
Thanks
Jules
I have a animation to render and wondered if someone could give me advise on the best uhd cache settings?
The shot is fairly simple, it's just a camera moving down a corridor with white walls either side, and a glossy concrete floor. The shot is about 200 frames long.
What would be the best approach for the HD Cache? Should I be using load and try to append? If so how would I go about this? Am I right in thinking I would render out 10th or 20th with settings: calulate from scratch - save to file, then render out every frame using settings: try to load and append - save to file?
I'm still a little confused about how try to load and append actually differs to load from file.
Thanks
Jules
10
[Max] General Discussion / Re: Volumetric/SSS rendering playground
« on: 2015-06-18, 16:43:33 »
With receptivity as one it is much better I must admit: 
When I posted material snip I was using version 1.00.02.
I have always used Maxwell render for sss so these artifacts are new to me. Thanks for the help!
When I posted material snip I was using version 1.00.02.
I have always used Maxwell render for sss so these artifacts are new to me. Thanks for the help!
11
[Max] General Discussion / Re: Volumetric/SSS rendering playground
« on: 2015-06-18, 16:32:36 »
One more: 
Render settings default, standard cube 40x40x40mm, white scene environment, same material as before.
I cant help but feeling it is down to the fact that there is no coefficient parameter. when I remove the scattering effect the cube renders pure black because of the very shallow attenuation.
Render settings default, standard cube 40x40x40mm, white scene environment, same material as before.
I cant help but feeling it is down to the fact that there is no coefficient parameter. when I remove the scattering effect the cube renders pure black because of the very shallow attenuation.
12
[Max] General Discussion / Re: Volumetric/SSS rendering playground
« on: 2015-06-18, 16:14:48 »
All render settings default, Corona version: 1.01.00 3dsMax 2015
13
[Max] General Discussion / Re: Volumetric/SSS rendering playground
« on: 2015-06-18, 14:39:41 »
Sorry. Yes I mean the dark outer edges. In all of my tests I have not been able to get rid of this.
This material has 2mm attenuation, 128 gray attenuation color and 128 gray scattering color. The box is just a newly generated box, the other geometry was re-smoothed using 'auto-smooth'
This effect remains even when the corners have been chamfered, it seems like the problem is consistent with sharp corners in general
This material has 2mm attenuation, 128 gray attenuation color and 128 gray scattering color. The box is just a newly generated box, the other geometry was re-smoothed using 'auto-smooth'
This effect remains even when the corners have been chamfered, it seems like the problem is consistent with sharp corners in general
14
[Max] General Discussion / Re: Volumetric/SSS rendering playground
« on: 2015-06-18, 13:23:13 »
Has anyone else had problems like this? 
some Metals also seem to also have a wierd dark edge but presumably for different reasons. I cant seem to get rid of it unless I make the attenuation colour very dark.
Thanks
Jules
some Metals also seem to also have a wierd dark edge but presumably for different reasons. I cant seem to get rid of it unless I make the attenuation colour very dark.
Thanks
Jules
15
[Max] I need help! / Re: Bucket Mode settings in depth?
« on: 2014-10-04, 18:04:39 »
Thanks Maru,
Sorry, I had a look on the forums but maybe not hard enough.
That makes far more sense to me now, thanks for taking the time!
Sorry, I had a look on the forums but maybe not hard enough.
That makes far more sense to me now, thanks for taking the time!