Background Render Problem, etc.

[Anonymous]

Ok, I feel a little silly asking this because obviously I'm doing something so simple so wrong.

1st question:
When I select a background image to render over, the model renders "behind?" the background - what setting am I missing?

2nd question:
It's been a while since I've rendered over backgrounds within ArchiCAD. In the past you were able to save your renderings as tif files and have the modeled portion save with an alpha mask. I don't see this option any more. Did it go away???

Thanks,
Dan K

[Anonymous]

Dan wrote:
1st question:
When I select a background image to render over, the model renders "behind?" the background - what setting am I missing?

2nd question:
It's been a while since I've rendered over backgrounds within ArchiCAD. In the past you were able to save your renderings as tif files and have the modeled portion save with an alpha mask. I don't see this option any more. Did it go away???

Oops! i'm going to answer one of my own questions - I should've searched a little more before I posted the question.

Regarding the background question, I found the answer here:
http://archicad-talk.graphisoft.com/viewtopic.php?p=25953&highlight=alpha+channel#25953
This is most definitiely a bug - I wonder if it will be fixed befor version 10. Anyone know of any upcoming maintenance releases?

Regarding the alpha mask question:
This function was last useable in ArchiCAD 7.0. It no longer worked as of 8.0. I'm not sure why they took it away - it was very usefule for quickly swapping backgrounds during post image editing. Where and/or who can we request that it be put back in?

Thanks,
Dan K

[Anonymous]

dan

1 - i don't think it's a bug exactly. the image you're using is a jpeg so no alpha channel. like the thread said unticking the 'use alpha...' checkbox will give the result you want. i suppose ac is just 'guessing' that the non-existent alpha is totally opaque

2 - works fine for me (ac8). seems to output the alpha channel automatically. have you checked the tiff file in photoshop or similar?

bill

[Anonymous]

bill wrote:
1 - i don't think it's a bug exactly. the image you're using is a jpeg so no alpha channel. like the thread said unticking the 'use alpha...' checkbox will give the result you want. i suppose ac is just 'guessing' that the non-existent alpha is totally opaque

Bill,
you're right... its not exactly a bug if your background image is a .tif file. It is a bug ,however, if your background image is a .jpg file. I guess you just have to know (one of those undocumented req's) to be sure and leave "Use Alpha channel for Transparency" unchecked when you are using .jpg background images. Kinda' funny that all of the Background images in the standard library are jpg's and this requirement is not documented.

bill wrote:
2 - works fine for me (ac8). seems to output the alpha channel automatically. have you checked the tiff file in photoshop or similar?

Yes, I had previously opened the images in photoshop and there was no selection to load. Strangely enough, however, they now seem to work. They actually started working after I had loaded my first background image as a .tif file...maybe the file was somehow "blessed" after I tried the first .tif background. I would be curious to know if other users who have never loaded a .tif file background have experienced the same issue.

Thanks,
Dan K

[Anonymous]

dan

1 - the most logical solution would be for the 'use alpha...' checkbox to be greyed out if the background has no alpha. maybe someone at gs could fix that

2 - worked with a jpeg for me. dunno why it didn't work for you

bill