Combine HSV node #52772

New Issue

M · 2017-09-15T23:29:44+02:00

M commented

2017-09-15 23:29:44 +02:00

Combine HSV node appears to produce inaccurate results.

Open a clean (incl. cache and configs) Blender instance.
Select Cycles Render
Select the cube in the scene and add a material
Use Emission shader as Surface instead of Diffuse (doesn't matter really)
Add Checker texture into color slot of Emission shader
Select color H: 0.750 S: 1.000 V:1.000 as Color 1 in Checker texture node
Add Combine HSV node, enter same values as above into Combine HSV node
Plug in Combine HSV node to Color 2 input of Checker texture
Preview/Render cube

Result: Checker texture appears as shades of purple/pink
Expected: Checker texture should not be visible, should be seen as solid purple color

Render Engine: Cycles
Feature Set: Supported
Device: CPU (where applicable) and GPU (where applicable)
Unexpected result in: Blender 2.71, 2.78c, 2.79 (the tested versions)
Expected result in: Blender 2.70

OS: Ubuntu 16.04

Might be related to: #41287

Combine HSV node appears to produce inaccurate results. 1) Open a clean (incl. cache and configs) Blender instance. 2) Select Cycles Render 3) Select the cube in the scene and add a material 4) Use Emission shader as Surface instead of Diffuse (doesn't matter really) 5) Add Checker texture into color slot of Emission shader 6) Select color H: 0.750 S: 1.000 V:1.000 as Color 1 in Checker texture node 7) Add Combine HSV node, enter same values as above into Combine HSV node 8) Plug in Combine HSV node to Color 2 input of Checker texture 9) Preview/Render cube Result: Checker texture appears as shades of purple/pink Expected: Checker texture should not be visible, should be seen as solid purple color Render Engine: Cycles Feature Set: Supported Device: CPU (where applicable) and GPU (where applicable) Unexpected result in: Blender 2.71, 2.78c, 2.79 (the tested versions) Expected result in: Blender 2.70 OS: Ubuntu 16.04 Might be related to: #41287

M commented

2017-09-15 23:29:44 +02:00

Changed status to: 'Open'

M commented

2017-09-15 23:29:44 +02:00

Added subscriber: @dlenber

M changed title from ~~Combine HSV~~ to Combine HSV node

2017-09-15 23:48:51 +02:00

Sergey Sharybin was assigned by Joshua Leung

2017-09-16 07:37:49 +02:00

Sergey Sharybin commented

2017-09-18 08:39:21 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2017-09-18 08:39:21 +02:00

Sergey Sharybin commented

2017-09-18 08:39:21 +02:00

Added subscriber: @brecht

Sergey Sharybin commented

2017-09-18 08:39:21 +02:00

This is in fact related on #42888, also 1549fea, c5927cd.

The issue here is that Blender interface considers HSV to be specified in linear space, which means typing (0.75, 1.0, 1.0) will convert color to linear space before storing it in shader. But Combine/Separate HSV operates in linear space, meaning there is no linearization involved when those nodes are converting HSV to RGB value.

This is just how Blender currently works, and there is no simple solution here without causing regressions. So thanks for the report, but it's not really a bug.

P.S. Maybe @brecht would love to revisit this at some rainy day tho :)

This is in fact related on #42888, also 1549fea, c5927cd. The issue here is that Blender interface considers HSV to be specified in linear space, which means typing (0.75, 1.0, 1.0) will convert color to linear space before storing it in shader. But Combine/Separate HSV operates in linear space, meaning there is no linearization involved when those nodes are converting HSV to RGB value. This is just how Blender currently works, and there is no simple solution here without causing regressions. So thanks for the report, but it's not really a bug. P.S. Maybe @brecht would love to revisit this at some rainy day tho :)

M commented

2017-09-18 09:34:02 +02:00

Hello Sergey!

Thank you for taking your time to address this issue! Also thank you, your colleagues, all contributors, the bug reporters, the wonderful community and of course the man that started it all, Ton. You guys have given us a tool to express our ideas.

As far as this non-bug goes, I have to say that I don't quite understand what you wrote. Might I suggest that the various HSV input types are renamed until this is addressed (HSV Linear/HSV Non-Linear) or even if it is not addressed at all? This way we, the users, could understand from the UI itself that different results will be obtained from different HSV input types.

However you choose to proceed, don't mistake my suggestion for any critique. Blender is awesome.

As a last request regarding this issue: is there a formula through which I can produce the expected results, ie. I input 0.750 into an input field and through the use of various math nodes I obtain the hue value which will produce the expected results? I'm asking because you seem to understand what this issue is and I still don't despite reading your comment multiple times.

Hello Sergey! Thank you for taking your time to address this issue! Also thank you, your colleagues, all contributors, the bug reporters, the wonderful community and of course the man that started it all, Ton. You guys have given us a tool to express our ideas. As far as this non-bug goes, I have to say that I don't quite understand what you wrote. Might I suggest that the various HSV input types are renamed until this is addressed (HSV Linear/HSV Non-Linear) or even if it is not addressed at all? This way we, the users, could understand from the UI itself that different results will be obtained from different HSV input types. However you choose to proceed, don't mistake my suggestion for any critique. Blender is awesome. As a last request regarding this issue: is there a formula through which I can produce the expected results, ie. I input 0.750 into an input field and through the use of various math nodes I obtain the hue value which will produce the expected results? I'm asking because you seem to understand what this issue is and I still don't despite reading your comment multiple times.

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Combine HSV node #52772