Projection map slot in Corona Light

[Jpjapers]

Corona Lights would benefit from the ability to apply (edit: and focus!) a projection map.
Ive found myself doing alot of stage lighting work recently and needing to simulate things like gobos.
Currently i cant see a way to achieve a gobo with a corona light. It can be faked with standard and photometric. But neither of them provide a full solution.

I can use photometric lights, however the intensity settings are completely incorrect when using corona shadows in a photometric light (i had to crank the photometric light to 450,000 lumens to match the 3000 lumens of the corona light with the same IES).
They also require an IES profile to appear in volumetric materials and passes.

Whilst i understand that a projection map is a 'fake'. If the only way to achieve the desired result of a gobo filter, is to use a photometric light, with corona shadows and a projection map.
Then you also have to eyeball the light intensity, surely corona can provide a better solution than that natively because at that point its compounding three or four fakes to achieve a shaped volumetric ray which could be achieved in corona by allowing users to adjust focus of the texture you can currently apply to corona lights.

It would need to work in conjunction with the IES profile for it to be fully featured.

I have attached a quick render demonstrating why none of the currently available methods we have are fully featured and arent suitable for achieving physically based gobo effects with IES and volumetrics. Something that is fairly important in the stage lighting space.

[Aram Avetisyan]

Few notes:
• Even if there is projection slot in Corona light (note that Corona light can be textured, which is the analogous effect of it, but giving far from "expected" results, as the further away from surface the light source is, more blurred the projection is), the volumetric effect would still need to be achieved. The way to do it with Corona light is to use volumetric materials (do it physically accurate), which will still be long to render. And even longer with many lights.

• As the result/effect is a fake, there is no point to care about physically accurate units and intensities I believe. Of course it would be nice to mimic as close as possible the effect of a, say, 3000 lumen/lux light, but in CG it is almost always about making things looks nice than making things look like they have correct setup.

• Standard light with volume light effect and CoronaShadows does "filter GI rays" from the projection map. You need to have the light color set to white and the rays will be colored as the projection map, see the attached image.

So, remember that Corona is targeted for physically accurate rendering, while keeping things as fast as possible.
Projection functionality in Corona Light will bring what you want to achieve closer, but in fact push it further from usability, because impractically long render times because of volumetric material used with Corona Lights, which should produce ultimately volumetric effect, and little to no illumination.

The compromise is acceptable I think - use standard lights with volume light effect, which (+) Render fast, (+) have GI rays from projection map, (-) unfortunately no IES support, but pretty neat hotbeam and falloff control, and (-+) with no physically accurate units, which are not quite needed.

I will gather all this information and create a feature requests, to see what is feasible to do in this direction, and we will use this thread for the updates, but please keep in mind that this has a low priority.

[TomG]

And great results are possible with this current workflow :)

https://forum.corona-renderer.com/index.php?topic=39730

Cheers!

[Beanzvision]

Very cool indeed! :)

[Jpjapers]

• As the result/effect is a fake, there is no point to care about physically accurate units and intensities I believe. Of course it would be nice to mimic as close as possible the effect of a, say, 3000 lumen/lux light, but in CG it is almost always about making things looks nice than making things look like they have correct setup.

A gobo infront of a light is a real thing that happens in reality in basically every stage production. The result might be fake currently, but thats only because corona light implements it that way. Light shining through a mask still has an intensity associated with it. If you put in a black and white gobo mask, the light in the unmasked areas should still be the desired intensity. There absolutely is a point in using physical units for this.


"in CG it is almost always about making things looks nice than making things look like they have correct setup"

This is a fairly ignorant position to take from an employee of a rendering company that gained its success from physically based rendering without compromise. Ive been doing this for a decade and advocating for corona since beta 0.7 because of the fact that from day 1 it was focussed on accuracy and physically correct rendering and not tweaking dozens of settings to create fakes to make things 'look nice'. Looking nice in large parts of the industry is a by-product of being physically correct and photorealistic. They are not separate end goals. Why would you as a company be so concerned with keeping things physically based and 'unbiased' if you think that as CG artists we only want to make things "look nice". There are amazingly well known and talented artists out there who push their physically correct workflows to the nth degree with as few compromises as possible. The entire design visualisation process is about showing clients what the thing they're building/designing actually looks like as best you can. Not showing them an idealised version of what they want to see. If youre using CG as an iterative design tool as many of us do, then making things look correct rather than look nice is the ONLY requirement.

• Standard light with volume light effect and CoronaShadows does "filter GI rays" from the projection map. You need to have the light color set to white and the rays will be colored as the projection map, see the attached image.

This isnt what i was saying. The volume light effect being a post process effect provides no GI into the scene FROM the volume rays because it is not scattering light through an actual volume. Its not about making it a colour. I dont know where the "filter GI rays" quote is from but Its about getting that indirect lighting from the volumetric rays into the scene that actually light the atmospheric haze within the space.

So, remember that Corona is targeted for physically accurate rendering, while keeping things as fast as possible.
Projection functionality in Corona Light will bring what you want to achieve closer, but in fact push it further from usability, because impractically long render times because of volumetric material used with Corona Lights, which should produce ultimately volumetric effect, and little to no illumination.

The projection map feature may be a fake as it currently stands. But having a masked light via a gobo disc is very normal across all of stage and theater.

The issue that we face with the currently available workflows is that none of them are actually providing the features or level of control needed. With corona lights specifically, without producing the full 100% perfect glass lens setup, and using full caustics. We cannot currently do any gobo-based stage lighting setups in Corona because it doesnt allow for masking of the light shape + IES. Placing a plane with a texture on infront doesnt do this either. Its because of the lens array demonstrated in the diagram attached. Whilst applying a texmap and setting directionality to 1 does show a map if you put the light really close to a wall, i cant see a use for this feature in actually masking the light shape.

In reality, stage lights have a focal length at which the gobo filter is placed, and then a diverging lens corrects for the focal length which expands the light cone into the specific coverage we see in the IES (which is why the IES is so important in the process). If corona lights had a better implementation of the texmap whereby it actually fully masked the light at the source (which would make that feature immeasurably more useful) then this wouldn't be an issue that needs a separate slot and i think could be a great addition. As it stands, even with a texmap and 100
% directionality and no IES, the texmap is not focussed correctly.

Render times are only impractical if you aren't planning for them to be long. I know that if i want to show a client their lighting setup in the space they have designed with the desired level of atmospherics i will need to render for a long time and thats just part and parcel of the process.

Keeping the renderer as fast as possible is your job sure. What we do with it as users isn't really for you to worry about. Ive been using corona basically every working day for a decade and know at this point how long things take to render and I know that if I want to show proper volumetrics in a space I need to set aside far more time to render just like we all do for caustics. Not only that, but volumetrics aside theres still no workflow to project a gobo with physically correct intensity AND use an IES.

The compromise is acceptable I think - use standard lights with volume light effect, which (+) Render fast, (+) have GI rays from projection map, (-) unfortunately no IES support, but pretty neat hotbeam and falloff control, and (-+) with no physically accurate units, which are not quite needed.

Hard disagree im afraid. Not only is IES a major requirement for stage lighting (every manufacturer provides dozens of IES for basically every fixture because of the lenses they feature), Physically correct units are also needed because you need to limit lights to their spec sheet data so you know how bright it can be. It also does not allow for a lit volume haze in the space as would exist in reality.  As many others have requested over the last ten years, its a feature that would be very useful in stage and theater visualisations. The workaround isnt suitable for that use case at all and i dont think its your place to tell us as users what is and isnt needed in our workflows either.

TL:DR

To be able to create ANY masked light (Gobo) effect currently, there are no options that provide the full feature set required outside of building a full lens array with caustics. None of the available options provide the ability to use physical light units, a projection map (or gobo light filter) and an IES file together and none of the proposed 'compromises' address the actual feature request or provide the required end result. Putting a plane over a corona light with an assigned IES does not create the correct result because of the issue around the focal plane.

In an ideal scenario, the corona light would have the ability to apply a mask to the light that can be focussed and blurred independently and allow it to mask the projected IES shape. This would allow stage and theatre lighting to be correctly reproduced essentially across the board as well as other helpful workflow tools such as applying animated tree shadows or fake caustics.

See attached examples showing how a gobo light works and the exact effect that i think would be a great addition to the tools corona has to offer.

[Jpjapers]

And great results are possible with this current workflow :)

https://forum.corona-renderer.com/index.php?topic=39730

Cheers!

Yeah thats very cool and the renders look really nice but chances are the deliverables aren't the same as mine in this instance. Nor are they likely to be an accurate representation. They look like really great marketing visuals. What I'm looking to achieve from a design visualisation perspective is to show as accurate a representation of my clients specs as possible and because of the current limitations in all available lighting methods, thats not possible for a stage lighting setup. I don't see any gobos in those renders though that may be down to their design not including them. I just see volumetric rays and an IES.

[Basshunter]

This is a fairly ignorant position to take from an employee of a rendering company that gained its success from physically based rendering without compromise. Ive been doing this for a decade and advocating for corona since beta 0.7 because of the fact that from day 1 it was focussed on accuracy and physically correct rendering and not tweaking dozens of settings to create fakes to make things 'look nice'. Looking nice in large parts of the industry is a by-product of being physically correct and photorealistic. They are not separate end goals. Why would you as a company be so concerned with keeping things physically based and 'unbiased' if you think that as CG artists we only want to make things "look nice". There are amazingly well known and talented artists out there who push their physically correct workflows to the nth degree with as few compromises as possible. The entire design visualisation process is about showing clients what the thing they're building/designing actually looks like as best you can. Not showing them an idealised version of what they want to see. If youre using CG as an iterative design tool as many of us do, then making things look correct rather than look nice is the ONLY requirement.

Amen to every word you said. Can't agree more.

Yeah thats very cool and the renders look really nice but chances are the deliverables aren't the same as mine in this instance. Nor are they likely to be an accurate representation. They look like really great marketing visuals. What I'm looking to achieve from a design visualisation perspective is to show as accurate a representation of my clients specs as possible and because of the current limitations in all available lighting methods, thats not possible for a stage lighting setup. I don't see any gobos in those renders though that may be down to their design not including them rather than a limitation.

Same case here. Result in that video might look "good" but it's not accurate at all. Also, I could never use this workflow where so many things need to be composed and faked to look good for one angle only. My job usually require me to use interactive render to show my clients different angles in real time as they send their inputs until lights are setup correctly. So I need lights to look as they should straight from the IR, no time for post.

As I've mentioned in other posts, it's not even possible to recreate an accurate Moving head beam effect with current Corona Lights. not even a simple gobo. And trust me, that "trick" of using real geometry with light material on it to recreate lasers or other types of stage lights like moving heads with fog will fall apart pretty easy as soon as you change the angle or need to show how that light beam hits a surface. Not to mention that it will produce inaccurate results making the room look way too bright.

[Juraj]

I would be also fan of this. I currently use two approaches for this, though neither is exactly the same as written above. For soft-boxes, I use texture-slot in CoronaLight. There is no focusing of course.
For distance focused Gobo, I use Parent-linked opacity textured place in front of CoronaLight. Kind of flexible but somewhat hassle as well.

[maru]

Hi guys, as far as I understand, this is what you would like to request:

- a Corona-native feature (e.g. in a Corona Light)
- ability to apply a projector texture to a light
- the projector texture would not get blurred as it gets farther away from the light source, like with the "keep sharp pattern" option for IES (or this behavior could be optional so we could decide if we prefer blurring or always staying sharp)
- additionally, IES option would be still available and IES would interact with the projector (the projector mask would block the IES pattern)

The goal is to simulate a gobo effect, which currently would have to be simulated using glass lenses and caustics, which is not a viable workaround.

Is the above description more or less correct?

[Jpjapers]

Hi guys, as far as I understand, this is what you would like to request:

- a Corona-native feature (e.g. in a Corona Light)
- ability to apply a projector texture to a light
- the projector texture would not get blurred as it gets farther away from the light source, like with the "keep sharp pattern" option for IES (or this behavior could be optional so we could decide if we prefer blurring or always staying sharp)
- additionally, IES option would be still available and IES would interact with the projector (the projector mask would block the IES pattern)

The goal is to simulate a gobo effect, which currently would have to be simulated using glass lenses and caustics, which is not a viable workaround.

Is the above description more or less correct?

Hey Maru,

Just a slight correction on one point. The projector texture would ideally have a blur parameter so it can be focussed and defocussed. With gobos for things like mottled effects its often the case that the clients will want to defocus them to remove the harsh edges from whatever pattern theyre projecting. The images ive attached show the initial manufacturer gobo image, then a gobo blurred in photoshop and then assigned to a photometric light shining through a Corona folume fog material. Obviously without the IES masking. Ideally the blur would be driven by a parameter rather than needing to produce a different texture.

Other than that, yes the projector map should interact with the IES and block it. As far as i can tell, stage lighting IES represent the shape of the cone as defined by the lens that is fitted into the fixture rather than the shape of the light output at source. The light would have been masked by the gobo prior to hitting the lens.

It may also be useful to have left/right/top/bottom 'barn doors' which would just be straight lines to crop the light as required though this could be achieved with a texture applied in the map slot if necessary.

Due to the nature of how stage lights are constructed with the different lenses and with the light being masked prior to the cone being defined, the current method to achieve this in a physically correct manner would be to build an actual lens array which is of course impractical and insanely technical. Or to fake it with one of the numerous methods above but none of them allow you to mask the IES itself.

If you do ever get round to developing this, ROSCO are a major manufacturer of gobos and for my purposes i often image trace their product images in illustrator to get a higher res image. Source 4 are a stage lighting manufacturer and they provide all of their IES files for their fixtures. The series 3 being a major one in stage and theater. So the testing data would be there for you. I would also be more than happy to give feedback via the dailies if this ever makes its way there.

Thanks

[Aram Avetisyan]

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