[fv]

I was wondering if someone can explain the alpha render channels and what is meant by "embedded".

I would like to render the full image with background and a seperate render with only the alpha channel. Now as I understand I have to render the image twice, once for the complete rendering and once for the alpha.
Now when I check the apha channel my rendering comes up with a black background and when I check embedded the Maxwell gives me the message that the render format does not support embedding an alpha.

Someone who knows more about this could help me out a lot, the manual is not very clear on this matter.
Francois

[Richard]

Mate you may have to select tiff or tga for the output format rather than jpg?

You are right - when you enable alpha you get a black background and need to render the scene twice to get a full sky option! Would be nice if this could be an embedded feature. A work around is to export the material or object ID along with the full render and select your sky mask from that with a one or two pixel expansion to erase the pixel bleeding at the silhouette!

[brodie_geers]

I ran a couple tests with the demo version. Basically Maxwell will embed the Alpha into the main image which should save you a step in post processing. Some formats, like .jpg's that Richard mentioned, don't support alpha channels though. When I saved my image as a .tif it saved the alpha as a separate channel within the image which makes it a bit easier to delete the background in Photoshop ( for instructions see http://graphicssoft.about.com/od/photos ... _2fwks.htm ). If you save as a .png though it'll save you an extra step by automagically getting rid of the background for you (giving you a nice transparent background to work with). PNG's also tend to be smaller than .tif's and are lossless making them my format of choice

-Brodie

[Richard]

Brodes? Does the sky though still come out black?

[stefan_kaplan]

Just be aware that the alpha channel might seem fully white in areas with non-transparent objects - as it should be.
But if you run Levels on the alpha-image in Photoshop, it sometimes needs a little more contrast to get completely white (depends on render time I guess).
When you render a .png with an embedded alpha, the render-channel and alpha-channel are automatically put togeather and your rendering might be a little tiny bit transparent.

If you have the same render twice, put on two layers in Photoshop you can see the difference by turning one of them on and off

Therefore I always render alpha seperate from the render it self.

When using alpha for clipping I love the "Remove Black Matte"-option in Photoshop:
1. Open your render-image and your alpha-image in Photoshop.
2. Go to the alpha-image and select all (Ctrl+A) and copy (Ctrl+C).
3. Go to the render-image. Double-click the "Background"-layer and press Enter (in order to release the layer from being a background).
4. Click the "Add Vector Mask"-button below the layers ()
5. Alt-click the new white layer-mask that has been added (in order to see the mask)
6. Paste (Ctrl+V) the alpha-image onto the layer-mask.
7. Right-click the layer mask and choose "Apply Layer Mask".
8. Go to Layer>Matting>Remove Black Matte (in order to remove any black at the edges). This only works when nothing is selected (deselect with Ctrl+D).
Good luck.

A work around is to export the material or object ID along with the full render

Never underestimate the power of Material ID and Object ID channels!

/ Stefan

[brodie_geers]

Richard,

Yeah, unfortunately the background still comes out black. I never have understood the idea behind that.

The advantage, I think, to the alpha over the MaterialID is that the alpha will "perfectly" blur the transition between your object and the background. That is, there are typically some pixels on that edge that are transparent. You can fake that with feathering but it doesn't look quite as good to me typically. Sometimes I'll run the render and then run the alpha separate, which by itself goes very fast.

-Brodie

[Richard]

Mate I've started doing most of my material id maps and the alpha at the same time direct from SU, works better for me as the Material ID from maxwell 50% of the time comes out grey scale, which is generally bloody useless!

I just delete the textures from the SU materials and then make them very distinguishable primary like colours, export a high res image and then close the scene without saving! The result is SO much better!

[fv]

Big thanks for all the info on this matter. Saves me a lot of trial and error time.

Its a pity the Maxwell manual is actually useless, no info on for example "embedded" channel or what tje results are like when you use the channels or what the actuall rendertimes will be like when using channels.

Good thing there is a forum and participating members...

[brodie_geers]

Richard. Interesting. The SU camera matches the Maxwell camera that much eh? I always assumed they were a bit different since SU isn't really using physical characteristics. Do you use the film/stage plugin w/ SU?

-Brodie

[Richard]

Richard. Interesting. The SU camera matches the Maxwell camera that much eh? I always assumed they were a bit different since SU isn't really using physical characteristics. Do you use the film/stage plugin w/ SU?

-Brodie

Mate the camera matches perfectly now, no I just use SU's normal camera.

I thought about your method of running the alpha separately and remember comments by Tom that the alpha gives an exact edge when used in combination with the black background. I find rendering with the black background a real pain for getting lighting correct. My workaround is to render with the normal sky then from either the Material or Object ID or that I generate from SU - I select the sky, delete it from the render and then expand the selection 1-2 pixels and do a subtle gaussan blur. If you leave the edge sharp it looks very cut in!

[Mihai]

Yeah, unfortunately the background still comes out black. I never have understood the idea behind that.

Why it has to premultiply the render with black in order for the alpha cutout to work correctly has been covered to death on this forum
http://www.maxwellrender.com/forum/view ... =3&t=24020

It seems to me you are making an overly complicated workflow. Not being able to see the brightness of the sky to get the right lighting on your building/objects doesn't seem an issue to me because what is important is getting the exposure right on the building itself, not the sky.

Mate I've started doing most of my material id maps and the alpha at the same time direct from SU, works better for me as the Material ID from maxwell 50% of the time comes out grey scale, which is generally bloody useless!

I just delete the textures from the SU materials and then make them very distinguishable primary like colours, export a high res image and then close the scene without saving! The result is SO much better!

This is an unecessary step in V2, you can set custom matID/objectID colors now from the material properties/object properties. I don't know if you can set this through the plugin yet, but if you use standalone mxm files, I guess you would set the material ID color in the mxm file itself, through mxed.

Sorry about the manual, it really wasn't time to get into a bit more detail about some options. It will be revised. As mentioned the embedded option will simply embed the alpha channel in the formats that support it, like tif, instead of rendering out a separate file. In the case of png, which doesn't support an alpha channel but does support transparency, your render will already be "cut out". You have a compositing example showing also the different channels on pages 73-74 of the manual.

[fv]

Tx Mihia,
its all clear to me now. Indeed the manual needs a little firther work.

I hope my question about the SU plugin stalling with autoMXM checked will be solved as well.
Francois

[Richard]

Hey Mihai

Thanks for the eyes up on the ability to set the material Id for each material!! What a BRILLIANT inclusion! Thanks NL!!!

This will be a dream now as once the ID is opened in PS you can use an action to generate masks for all materials which will certainly speed post editing!

[brodie_geers]

Great idea about the action Richard! I'd never thought of that. Can't wait to give it a shot as that would speed my workflow considerably!

-Brodie

[Richard]

Great idea about the action Richard! I'd never thought of that. Can't wait to give it a shot as that would speed my workflow considerably!

-Brodie

It would be great if you could create a schedule of ID colours that any render would use by default on any materials running from first in scene to say 50 or 100 materials. That way you could be sure that your colours are broken up enough, as the problem will occur when using an action if a colour used by any of your materials in library are too close!