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If i use the sketchup plugin i often use the groundplane options. Do these exist in studio or do i have to import a primitive ? I am trying to render a car with hdri. I would like the shadows under the car but not the plane showing. I have tried searching the forums but i expect i do not understand the correct terminology. Is this something which can only be done in post processing & compositing ? Many thanks in advance.

Simon

A primitive 1x1 plane can be used (if you don't intend to use any displacement) which I then scale as large as needed (sometimes 1000 x 1000).

You can render the shadow pass and composite in post but you can't composite directly in Maxwell... it seems like alot of work but really once you get the process down you can do it very quickly.

In the Sketchup to Maxwell series I:

1) set up the shadow catching material and object options.
2) set the render options for both the render and shadow channel.
3) rendered to SL 10.
4) composite the render and shadow channel in Photoshop (showing 2 different methods).

All in real time, in less than 7 minutes -- and that was while I was taking the time to explain how to do each step...

Best,
Jason.

Thanks Jason.Which chapter is this workflow in ?

Okay i got it now Jason, however i am left with a small gap between the 2 layers i noticed you had this as well.



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There is a "half pixel gap" issue that sometimes will show up (in Maxwell 2.5.1) like this.

The explanation as I understand it is:

This happens when you have the shadow pass cut off exactly where the alpha is (as in HDR backgrounds) so there isn't a good match (due to the Anti-Aliasing of the edges) -- This issue would be more visible when the shadow is composited against a light-valued background.

See this topic: http://www.maxwellrender.com/forum/view ... 13#p342513

In some ways this is could also be related to this issue http://www.maxwellrender.com/forum/view ... 80#p330080 (and it's resolution).

Hopefully this issue will be resolved/fixed in the next patch.

Best,
Jason.

Okay, thanks again the car i found over at sketchucation in this thread if anyone is interested:

http://forums.sketchucation.com/viewtop ... 81&t=37831

I had somehow guessed it was anti-alias connected as the result was a lot better at double the resolution. I look forward to the next patch.

Simon

Chedda, separate issue, but you may have a gamma issue with that hdri background. I had this same issue with some Dosch backgrounds I'd bought awhile back where they had a baked in gamma of 2.2 rather than just leaving them at 1.0 where they should be. As I recall, opening them up in photoshop, applying a gamma of .45 and resaving solved this issue. Might give that a shot and see if the coloring on that background doesn't look less washed out.

-Brodie

Thanks for the advice Brodie i think your right it does look washed out.Do you use CS5 ? I opened the hdri then image,adjustments,hdr toning. It seems p-shop recognized the embedded gamma and set it back to 1.0 it instantly looked better. I suppose you calculated that .45 by eye ? Or was this mathmatical to get 2.2 back to 1 ?

I do use CS5. I still get quite confused about all the gamma talk. I look forward to the day when there's a more universal cohesive solution...a sort of unified theory that's adapted by all. Maxwell, thank God, takes out many of the complications a 3ds Max/Vray workflow inexplicably introduces, but you still get these issues occasionally, from HDR creators who can further complicate issues.

At this point, I typically know that a gamma is either going to be 1.0 or 2.2 and can usually tell the difference, particularly if it's a photo, and I adjust accordingly. In your case HDR's should be 1.0 because Maxwell will give it a 2.2 curve. If for some reason it already had a 2.2 curve, when Maxwell does it's thing, it means you'll have a gamma of 4.4 (I'm sure that's not actually how the math works out but you get my point - the gamma is too high giving it the washed out look). From what I recall PS will also apply a 2.2 gamma to a 32 bit image. So if it looks right in PS it should look right in maxwell.

The .45 is a mathematical thing. I think it's actually like .445 or something like that, maybe someone can help me out there. Basically 1.0 is a straight line, 2.2 is a curve that goes up a bit in the middle and .45 is the opposite (it goes down a bit in the middle by an equal amount). So applying a gamma of .45 to something with a gamma of 2.2 will straighten it back out to a line (gamma 1.0).

So, to your situation, if it looks right in PS, there may be some other issue. Is your background composed of a 32 bit .hdr image put into the Background slot of the IBL channel?

-Brodie

Here's a quick check i did, I bumped up the exposure by something like 2.5 and then isolated the background and applied the .45 gamma adjustment. I think it looks a lot better. There's certainly a gamma issue in there somehwhere.

-Brodie

Yes it's a 32 bit hdr image used as an ibl. No it doesn't look right in photoshop. However as soon as i open the hdr toning dialog it looks perfect as it is set as 1 by default.Thanks for the heads up Brodie. This is very confusing for me too especially as we have burn & gamma controls in the maxwell app as well. I have left them here as default HDTV 0.8 burn 2.2 gamma. Even though my monitor and colour space is apple srgb ?

I just double checked the PDF that shipped with the images they are not alike i presume i can rely on the image in the pdf ? I also suppose that these images can be tweaked to my liking and this is non destructive, or should i make duplicates.This thread has covered many topics already perhaps i should open a new one concerning gamma & hdri ?

Please note all these parameters can be set at any time and you can easily render once and output many combinations of file types/bit depths and any variations of the following settings (as well as Simulens effects)... an MXI file exists in spectral colorspace and as such is extremely flexible.

For tone mapping:

Colorspace will be largely dependent upon what you are doing with the images (eg print, web, or video/animation). For print (destination offset or sheetfed CYMK) I prefer to work with either Adobe RGB 1998 or Bruce RGB. For web use sRGB is the most appropriate. For video/animation output the PAL or NTSC options will be typically your best bet depending on where in the world you live (although sRGB can be appropriate in certain circumstances as well).

Burn is OK in a range between .5 and 1 -- the idea here is effect the blow-out of the highlights, higher values means more "blown-out" highlights.

Gamma for Apple is normal at 1.8 (2.2 is PC standard) -- the idea here is to control the midtones, higher values means brighter midtones.

If you are outputting HDR,TIF,PNG, etc. at high bit-depth (32-bit) then these setting will have less importance(none in the case of colorspace) as you can do all of them and more in Photoshop (with the exception of Simulens). Likewise if you are using the Photoshop plugin for Maxwell those settings will have less relevance because of the high bit-depth available to the tools in Photoshop in that workflow.

These tools really only have alot of relevance if you are working in 16-bit or 8-bit output and do not intend to do any post.

On the topic of IBL -- Any HDR/EXR IBL should have an gamma of 1 to give the proper information to Maxwell for rendering... any other value will skew the results of the Maxwell rendering process.

Best,
Jason.

Thanks a lot again Jason ! My only confusion is the presets within CS5. I open the washed out hdr, at default the gamma is set at 1 it looks good (not quite the same as the PDF image) Where does the .45 adjustment come into it ? Does CS5 recognize that the image already has 2.2 gamma somewhere in it's metadata ? I can confirm after reading Brodie's other thread that it is a dosch product also. Can you recommend any other sources for hdri ? I am aware that some cameras now have this feature built in (without bracketing) is this authentic ?

Where did the HDRI come from?

In my case, getting the images from Dosch, the PDF showed the correct gamma however the actual image file they gave me was wrong. Perhaps there's some program out there that benefits from having an hdr with a gamma of 2.2 baked into it, but I don't know what program that is. I set up a batch process in photoshop and changed all of the images I'd be using to gamma 1.0 and saved them over the originals. I'm not sure whether it's destructive or not, but if it is, it would be very minimally so and having the original file will only cause issues later on so I'd get rid of it. If you ever need to reapply a gamma of 2.2 down the road for some reason, you'll be able to do it in PS and won't notice the difference between it and the original file you deleted.

-Brodie

Here are a couple of my threads relating to these Dosch issues.

http://www.maxwellrender.com/forum/view ... 97&t=35639
http://www.maxwellrender.com/forum/view ... 97&t=35331

When you say, "at default the gamma is set at 1" what do you mean. How are you checking this?

-Brodie