Creating alpha channel texture in Photoshop

[Scott Bulmer]

Can't seem to get this process to work. Must be doing something wrong. Can someone refresh my brain please?


1 In Photoshop, select the area that you want to be opaque, using the magic wand or any other selection method. Note: The area that was not selected in the alpha channel will be transparent when the texture is used in Archicad.
2 Then in the ‘Select’ menu, choose ‘Save Selection’, and choose ‘New Channel’ in the current document file. An alpha channel now exists and can be seen in the ‘Channels’ pallet.
3 Save the file as a TIF since JPG does not keep the alpha information.
4 In Archicad, load the file using Library Manager (note: you can add it individually or preferably place it in the project library and reload the library using the library manager.)
5 In Options>Element Attributes>Materials, assign that texture to a new material, keeping proportions. Make sure ‘Transparency’ is checked under ‘Alpha Channel Effects’.

What am I missing? Thanks

[Dwight]

What rendering engine?

If lightworks, you must "Match Internal" to employ the alpha channel.

[Scott Bulmer]

Thanks as always Dwight,

LW was set to 'Match Internal Engine'. As it turns out, the original file I was using to create the alpha channel had some unknown problem where it would either improperly create an alpha channel file, or not render as expected in LW. Other files seem to be working correctly.

Separately though, would you kindly have anything else to add (alternate steps or recommendations) to the Alpha Channel creation procedure outlined in my earlier post, that may be useful to others.

[Dwight]

You've covered the fundamentals.

Except that "Match Internal" is not a setting, it is a command. When using the internal engine dialog to build a material as you have done, LightWorks won't change from whatever it was reading until you click the button. And this must be done every time you edit the internal engine material.

What I've learned from doing my seminars is that users fail to understand:

1: that the alpha channel is useful for bumps (mainly as shadows from shingle or siding edges) and creating transparent knockouts (say in knocking-out the spaces between leaves in foliage)
2: That your method of selecting areas uses the underlying image - the alpha channel can be arbitrarily drawn in for bumpy patterns or knockouts unrelated to the underlying image.
3: LightWorks defers to images with alpha channel masks - if you have an internal engine material with an alpha channel and check an alpha channel effect, Lightworks willuse this channel if you "match internal."
However, LightWorks doesn't need an alpha channel to create a bump map. It can create any effect using the RED channel in the image. SO, if you have an image lacking an alpha channel in the internal engine mode and switch to LightWorks ( matching internal) it will make the shingle bumpy.
4: Light Works and most superior renderers don't rely on alpha channels at all. This alpha channel behavior is a hold-ver to maintain the usefulness of old Archicad texture. What modern application do is employ a totally separate file as a maks - Look in the LightWorks parameters and you'll see a oplace for this file. "Matching Internal" will simply force LightWorks to refer to the internal engine image in employing the bump or transparent effect.
5: You'll also see that LightWorks can map images to form mirror and special color overlay effects.

So let me plug my book because it explains all of this in bettter detail. The pile is getting quite small, now, so I do advise you to order soon to avoid disappointment.