[brodie_geers]

I've been having an issue with the alpha's generated from maxwell lately, where they're leaving a thin black line around the objects.

Here's my process.
1. Open MXI in Photoshop
2. Copy Alpha
3. Create layer mask for render
4. Paste Alpha into layer mask

Below is the result (I added a green background for to emphasize the black silhouette).



If I do a Layer->Matting->Remove Black Matte it results in a white silhouette.



Or if I do a 1px defringe it can screw up the edge pixels a bit (particularly on areas like the handrail in the lower left)



So is there another way to apply the alpha, or am I otherwise doing something wrong?

-Brodie

[tom]

When you open Alpha, convert it to Greyscale document prior to start appying it. Because, when you copy paste the RGB Alpha, Photoshop cannot use it properly.

[brodie_geers]

Hrm. Not sure I understand. So when I bring the MXI into photoshop it opens everything in the same file. If I convert that file to grayscale, of course, I'll lose the color in my rendering. So are you're saying copy the Alpha, paste it into a new drawing, convert new drawing to Grayscale, Copy alpha again, and paste back into the original file? Or is there some other way?

-Brodie

[tom]

So are you're saying copy the Alpha, paste it into a new drawing, convert new drawing to Grayscale, Copy alpha again, and paste back into the original file? Or is there some other way?

Yes, I'm exactly saying this. Although, current plugin has a small gamma issue with alpha layer and it will be fixed in the next update. Until then you can do this:
1) Open MXI
2) Detele Alpha layer
3) Duplicate "Background Mask" layer and invert it (now you have the correct alpha)
4) Copy paste this new alpha into a greyscale document
5) Copy greyscale alpha and use it as layer mask
6) Apply mask and remove black matte

[brodie_geers]

I ran 4 tests. The first was through the method you describe, 2nd was w/o converting to grayscale, 3rd was using alpha instead of background mask converted to grayscale, 4th alpha kept as RGB.

Flipping between the 4 I can't spot any difference at all. I'm using CS5. Could that be an issue?

Background Mask Inverted Grayscale


Background Mask Inverted RGB


Alpha Mask Grayscale


Alpha Mask RGB


-Brodie

[tom]

Could you please open the MXI in Maxwell and save the channels separately as render and alpha, then try again or send me so I can check?

[brodie_geers]

Still no change with separate exports from Maxwell.

Here's a separate problem I've had with my latest batch of renders, which I bring up as perhaps it's related (or perhaps not).

I've had a couple alphas turn out like the render below.



They odd area on the right side is showing some incorrect alphas from some palm trees that are in the model. The palms were from 1.7 and it's entirely possible that the alpha on the leaves aren't very good. However what's behind the trees is solid building so the areas should still be all white.

A closeup of the object ID focused on that the palms (you'll notice that these aren't clipped properly either, but again that part is probably my fault).



-Brodie

[tom]

OK, the plants have problem with MXM setup (or the material id has problems with layer opacity) and you should check "opaque" option for alpha. For edges issue, I need a pair of images; the render and it's alpha saved from Maxwell.

Here's a successful example:

[brodie_geers]

Uploaded the full res .png versions to my dropbox. The zip file is like 19 megs.

http://dl.dropbox.com/u/384281/Raw%20Ou ... Images.zip

-Brodie

[tom]

Here it works nicely so, one question... Do you apply Layer Mask before calling Removal of Black Matte? (Layer / Layer Mask / Apply OR right-click on layer mask itself and Apply)

[brodie_geers]

Here are the steps...

1. Open MXI
2. Copy Alpha
3. Apply layer mask to Render (creates a blank why layer mask)
4. Alt+click layer mask to enter the layer mask
5. Paste Alpha

Typically I would just stop here, but since I need to get rid of the black outline...

6. Click layer mask -> Apply layer mask
7. Layer -> Matte -> Defringe or Remove Black Matte

-Brodie

[tom]

As I explained above, avoid using Alpha coming from MXI until it's fixed. Save out alpha from Maxwell directly OR use inverted version of "Background Mask" layer created by the PS plugin. Here, "Defringe" is not the correct option so you should use "Remove Black Matte". More here:
http://think.maxwellrender.com/maxwell_ ... n-110.html

[brodie_geers]

Ya, sorry, didn't explain right. Let me revise for the method which applies to the image above...

1. Open MXI - Save Render and Alpha
2. Open Render and Alpha in PS
3. Change Alpha to Grayscale
4. Copy Alpha
5. Apply layer mask to Render (creates a blank why layer mask)
5. Alt+click layer mask to enter the layer mask
6. Paste Alpha

Typically I would just stop here, but since I need to get rid of the black outline...

6. Click layer mask -> Apply layer mask
7. Layer -> Matte -> Remove Black Matte

I think the Above image is better than I was getting before an probably acceptable although I'm still seeing a bit of white halo, particularly along the aliasing in the upper left portion of this image.

-Brodie

[tom]

I think the Above image is better than I was getting before an probably acceptable although I'm still seeing a bit of white halo, particularly along the aliasing in the upper left portion of this image.

I see but I'm unable to reproduce this with another scene I have. Please, test with a simple setup when you have time. I'm not sure why in your pair it happens. Which platform are you using? OSX? What gamma does this render use?

[brodie_geers]

Windows 7. No special gamma, 2.2 I guess? I'm not at my work computer anymore.

-Brodie