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Topics - Ondra

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we would like to fix the black passes in DR problem before 1.6 is out. To do this, we ask all users who experienced this problem to answer these questions:

1) How often does the problem happen? Every DR render, most renders, occasionally, rarely, ...?
2) Do all slaves contribute to the problem, or just some? Is the problem always localized to some specific computers, or is it random?
3) Can you send us logs from DR server from the faulty slave computer?
4) are there any errors or warning displayed when it happens?
5) Can you use the "retain EXR" feature and send us the EXRs from the faulty slave?

This would really help us nail down the problem, thanks!

Chaos Corona for Blender / New standalone build
« on: 2017-01-17, 14:55:13 »
we automated the build process for standalone, so I made the first build that involves both legacy/fullspeed version, and release/assert versions. It is posted in the dropbox daily builds folder:

[Max] Tutorials & Guides / Corona Smart Tips
« on: 2016-12-12, 14:13:40 »
Some random smart tips that are probably not obvious at first sight. Feel free to contribute ;)
  • You can change language of tooltips in Render Settings -> System -> System Settings. We provide English, French, German, Italian, Russian, Spanish, and Ukrainian translations.
  • You can set up autosave of all renders every 10 or so minutes, and on render end, in Render Settings -> System -> System Settings. You can use the autosaved EXRs directly, or resume the render from them. This prevents data losses during long rendering on crashes and power outages. Autosave settings is shared for all scenes - i.e. you need to set it up only once.
  • You can use same variable in autosave filename as in render settings - for example "%d %f %n %v" will output datel, filename, frame time, and camera name
  • you can use CoronaColor in "Solid HDR color" mode with negative values to produce more saturated colors than RGB color picker would allow. The change is noticeable when using moderately to strongly colored light sources.
  • CoronaColor is faster to render than other methods of producing solid color from maps, such as empty Output or ColorCorrect maps, or RGB tint/multiply
  • You can save current scene settings as defaults from Development/experimental rollout with "Save defaults..." button.
  • You can doubleclick the image in Corona VFB to fit the VFB to current render size
  • You can add render regions in Corona VFB by just holding down shift + dragging in the viewport
  • When using Corona Color Picker, you can insert web colors (e.g. #00FF11) directly, allowing you to copy&paste from photoshop in single step. You can also pick any color from the screen (not just from 3ds Max) with the "Pick" option

There is a lot of confusion about the sRGB checkbox in color picker lately and why the same numbers can represent different colors. I will try to explain it.

General intro

Q1: Why is 127 gray sometimes darker and sometimes brighter? Why is 0 240 0 green sometimes greener?
A: Because there are different color spaces, terms such as "red 240 120 50" can mean different actual colors in different color spaces - Adobe RGB, Wide RGB, XYZ, CIERGB, sRGB, ... The reason why we can usually get around by just using numbers without specifying color space is that the sRGB color space is widely adopted and was set as the default for web graphics, leading to wide adoption.

Q2: Why not just always use sRGB then?
A: Because sRGB is "narrow" and can express only a relatively small subset of all colors without using negative values. It is also non-linear - there is gamma curve involved - you cannot add two sRGB colors in rendering (i.e. from 2 lights in the scene) and expect correct result. You need a linear space for that - this is what the linear workflow is about.

Q3: Why even complicate things with gamma?
A: Because human vision is highly non-linear - roughly logarithmic. By applying a gamma, sRGB is roughly perceptually uniform - adding 1 to a dark or bright color results in roughly the same increase in brightness. Linear gradient from 0 to 255 in sRGB looks roughly uniform. In '90s nobody was doing rendering (which needs linear color space as opposed to 2D graphics), converting between color spaces would be too expensive, and memory was scarce, so the 8bit gamma-baked sRGB modelled to match '90s CRT monitors was created to give good visual resuls for 2D graphics. 8bit non-gamma format would produce bad results because all of its 255steps precision would be wasted in blacks, with no precision left for whites. Also appylying the gamma before sending the image to monitors would be too expensive.

Q4: Why is this a problem in 3ds Max?
A: Because 3ds Max is not color managed, and does not have the concept of color spaces. It internally uses just "RGB" with no information about which space it is - which is problem because that number can represent different colors, and renderers cannot just use sRGB, as explained previously. The biggest problem is that certain map slots need linear data (such as diffuse color) to work properly (linear workflow), while other slots need sRGB data (normal, bump, and displacement) to preserve what user intended in photoshop when he created the map and saved it as sRGB. 3ds Max has no way to specify which space is the input texmap in, or what space it returns results in, which puts the burden of checking this on user. We try to make it easier for users by showing warnings in normal maps, but that is not an ideal solution.

Q5: Why do different textures need to be in different color spaces?
A: I will give an example: diffuse color vs. normal/displace map:
- Diffuse color is just a captured surface reflectance (assuming no reflections). The renderer internally has to multiply the diffuse color with incident radiance to produce bounced radiance when calculating GI/direct light. This multiplication will not work if done in sRGB color space, because it is not linear. When you created a photo of the wood/gravel/leaf, your camera added the gamma curve to the image when it was saved as .jpg - because that is what the standard requires. Renderer needs to remove the same gamma curve to get the true linear values.
- Normal map cannot be photographed in reality. It is drawn in photoshop, and the standard here (created in realtime graphics before linear workflow era) is that 127 127 255 saved in jpeg is "no change to normal". If we would remove the same gamma curve as from diffuse texture, then "no change to normal" color would become "huge change in normal", which would screw up look of the model because all normals would be way off. This is really easy to reproduce and I bet it happened to everyone at least once ;)
- When you draw a displacement map in photoshop and use linear gradient from black to white, you expect this to translate to linear slope on the surface. You save this gradient into JPG as linear progression from 0 to 255. If renderer would remove gamma from this and interpret the numbers as height then, the slope would no longer be linear, but gamma-curve shaped.
We would happily do these decisions for you on background, but that is not possible in 3ds Max - textures work as black boxes there, so we cannot determine how should each texture behave, when for example the same texture is instanced in different slots, reused in shader tree, ... Plus there is the issue of legacy workflows - people expect to load normal maps with gamma override - by not requiring gamma override we would break workflows people have because then overriding normal maps to 1.0 gamma would actually produce incorrect result.

Color pickers

Q6: Why is this an issue in color pickers?
A: Because there are exactly the same problems when picking color as when inputting a texture - you can think about color pickers as small 1*1 px textures ;) - you need to specify their color space the same way as for textures.

Q7: How does 3ds Max color picker work?
A: When gamma is set up properly in 3ds max, the color picker will show linear (no-gamma) sRGB numbers, show gradient which is linear in linear space, BUT show sRGB (color-mapped) colors on the monitor.

Q8: What is the problem with this?
A: We identified these problems:
- The color gradient on sliders progresses uniformly in the linear space, so it progresses non-linearly in sRGB, so it is perceptually non-uniform. You can see this - all blacks are cramped at the very top, half of the slider looks completely white.
- You cannot do direct input from photoshop/webpage/... Photoshop uses sRGB values. When you put them in the 3dsmax inputs, they get interpreted as linear values, resulting in brighter color. This leads to absurd situations where you would open a texture in photoshop, pick one if its pixels, write that color in 3dsmax, and get completely different results. Or putting 127 in color picker gives different result from putting 127 gray jpeg texture in the texture slot.
- Same goes the other way - if you pick color for material under white lighting, say 255 127 0, render, and copy the image to photoshop, the material will have much different green color value.

Q9: How does Corona color picker work?
A: With sRGB checkbox off, it works exactly like 3ds Max picker, with one exception: we made the sliders perceptually uniform - roughly half of the scale is dark colors, and half is light colors. When you enable the sRGB checkbox, then nothing changes (displayed color, sliders, ...) except for the numerical values - those are now in sRGB. This means that with sRGB checked, you can copy colors directly from photoshop/web/... with no brightness change.

Q10: Should the sRGB checkbox be on or off then?
A: There is no "correct" solution. Picking the colors visually works exactly the same in both cases. Only thing that changes are the numerical values. What is better depends on situation. Use sRGB=off for consistency with 3dsmax, sRGB=on when you need to match photoshop or web values.

Q11: This is confusing, but I want to use the new color picker because of temperature!
A: No problem, just leave sRGB=off to have the same behavior as 3ds Max color picker

"I cannot be bothered with technical details" version
When using Corona Color Picker, leave sRGB off. It will behave exactly the same as 3ds max color picker. When you copy RGB values between photoshop and 3ds Max and notice the result is not matching, turn sRGB on first, then copy the values. You can mentally rename the checkbox to "match numbers to photoshop instead of 3dsmax"

[Max] Daily Builds / Daily Builds 1.6
« on: 2016-10-10, 15:29:35 »
Let the new games begin! Major new feature in 1.6 will be new DR. We want to also do bugfixing, speed and memory optimizations.

One teaser to keep the hype going is attached

[Max] Daily Builds / 1.6 Daily builds changelog
« on: 2016-10-10, 15:27:35 »
Daily builds are available in the usual place:

So far just removing some dead code ;)

[Max] Daily Builds / New installer feedback
« on: 2016-09-28, 09:23:51 »
The latest daily shipped with new installer that features:
  •     Faster typical installation
  •     Installs required MSVC redistributables and specific windows updates automatically
  •     Can be uninstalled from program files
  •     Uninstaller more reliably cleans up all files, directories, and registry entries
  •     New pictures
Plese let us know if you find any problems or have any other comments about it!

We are thinking about removing/hiding this parameter as the denoising continues to work reliably without changing it in our tests. Is there anyone who changes its value?

[Max] Daily Builds / Scatter lister script
« on: 2016-09-19, 11:16:57 »
there is new script on the dropbox -

we want to bundle it with stable corona release, so give it a try and report all problems you find here!

After nearly 10 years I did a quick model/render just for fun - a 30 minute live demonstration of how 3D works to a friend. I was actually quite surprised how easy it is to make decent render in Corona with interactive, compared to what I remember 10 years ago :D. Though the model and materials are shit obviously ;).

News / Corona 1.4 hotfix1
« on: 2016-07-27, 10:23:51 »
We have just released hotfix 1 for Corona 1.4. It just fixes a single bug: decimal comma/point issues in 3ds max 2017. If you did not experience this issue, there is no need to update. Get it here:

[Max] General Discussion / Which 3ds Max version do you use?
« on: 2016-07-26, 16:10:04 »
Simple question ;). I am interested in this because I would like to remove support for 3ds Max 2011 and 2012 in the near future. It is getting to expensive to drag along the backwards compatibility... Also there are some improvements that we could do that would work only in the later 3ds max versions, and I would like to know what percentage of users would benefit from them

[Max] Daily Builds / 1.5 Daily builds changelog
« on: 2016-05-31, 18:38:08 »
First 1.5 daily, here we go!

  • CoronaBitmap open file dialog
  • Rayswitch mtl: displayed material in viewport changed by default to the directly visible slot, added option to change which one is displayed
  • Unchecking casts shadows in object properties now have more consistent effect - same as putting the material in rayswitcher in all but GI slots
  • Corona materials can now be displayed in viewport directly (max 2012+)
  • Non-color mapped render elements (world position, normals, velocity, …) are now saved linearly in EXR. This due to 3dsmax limitation also means that for proper saving to LDR the gamma has to be overriden to 1.0 in the file save dialog.
  • Embree memory usage is now printed into log
  • Added option to save current render settings as defaults
  • Better refraction lobe normalization: Making refraction glossy no longer darkens the material
  • Fixed rare crashes/unexpected behavior in VFB render history
  • Added filmic tone mapping and saturation controls
  • Added Corona proxy function for converting to mesh: CProxy.ProxyFp.duplicateToMesh

Hi all!
There were some bug reports on Corona scatter not behaving correctly in animation if the surface on which it scatters is animated - objects would randomly jump around. We fixed this by doing the scatter just in one frame and then deforming it in others - so all objects would "stick" when surface is animated

There are however some questions/issues:
  • If we scatter on a surface and then the surface stretches significantly, the distribution can become non-uniform. Is this OK?
  • What time should the scatter be done in? Always time 0? Or have a control (spinner) for it?
  • Should this mode be always on? Or should there be a checkbox to switch between the old and new way?
  • Avoid collisions: if the surface object moves, then 2 objects that did not colide in frame 0 can start colliding in frame 10. What should we do? If we reject one of the objects, then the "objects popping in/out" problem is back. if we let it happen, then "avoid collisions" can actually permit some collisions.

Let me know what you think, thanks!

[Max] Daily Builds / Daily Builds 1.5
« on: 2016-05-16, 21:00:15 »
Daily Builds Eligibility
  • Everyone with FairSaaS or Box with Subscription license now has access
  • No requests/applications necessary

How to Use Daily Builds

  • Get the Corona Universal Installer and install a regular version of Corona first, if you already havent done it already ( and activate the license.
  • Go to and download a daily build. They are located in folders named using the date they were created.
  • Select the appropriate version. You will need to pick a legacy version if the Corona Universal Installer displayed a warning that it will install a legacy version (this happens on most AMD and old Intel CPUs. All i7/i5/i3 can run the regular, faster version).
  • Copy over the 4 files (plugins/Corona201x.dlr, plugins/CoronaUtils201x.dlt,  CoronaLib_Release.dll, and Corona_Release.dll) to your 3ds Max root folder. Make sure that all 4 files overwrite the already present files.
If you want to have the Dropbox folder synchronized with your desktop dropbox app, instead of having to access it via web, send your dropbox email to

Daily Builds Changelog

There is a separate topic for that:,7238.0.html

Daily Builds Rules

  • USE AT YOUR OWN RISK. Daily builds may contain unfinished features and not be stable, may damage your scene, freeze your 3ds Max, make you miss your deadline. Reverting scenes from daily to stable builds might not always be possible! Always make backups of important projects. Use daily builds with caution and common sense.
  • NO OBVIOUS-BUG REPORTS IN THIS THREAD/SECTION. To report a bug, use the bug reporting forum section or Mantis bug tracker. Discussion "Is this a bug?" is fine, but if something is clearly broken, please use the appropriate channels.
  • NO REPOSTING UNFINISHED FEATURES. Although we do not require signing NDA beforehand, we ask you not to repost info/screenshots/videos on unfinished features outside of Corona website. It could make Corona look unfinished/unstable to outsiders. When in doubt, ask first before reposting.

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