I have a nice grid-like image I want to use to create an alpha (If alpha is what I need!) to use as a transparency jpg for use in rendering - so I can see under the floor! (through the grid)

Okay, I've selected what I want to use, saved the selection, created an alpha channel, only....

Is this the right way to do it?  is the selection the right way instead? (i.e. quickest) 

I have a totally different image for the floor already, I was planning on layering this image with that floor to give it a grid-like appearance - and the transparency would just punch the holes out to reveal what's beneath the floor.

The transparency needs to be black and white, that I do know.

I'm sure I must have done this before but my mind's a blank.

I just realised that I didn't make clear that I have already created an alpha channel (I called it "Matting") and I have saved selections of the holes and the inverse of the holes...

I'm just not sure how to actually get a jpg that looks like the black N white alpha channel, top left of the posted image.

That's what I need to do in the simplest manner - only how???

I been trying to figure this one out for a long time myself   This definitely a thread I will be following.

Good question  thanks for posting

I just hoped that there was a short cut of some sort.

I mean I can see that there's a way to do it with the selections, but it took me a while just getting selections of both the holes and of the inverse of the holes, without having a nasty gap between them - which involved a combination of expanding the selection of the holes, then expanding the selection of the inverse before I had selections of both that could be put together again without the fuzzy gap between them.

And that was such a trail and error process that I couldn't be sure of repeating it exactly... which made me wonder if there might be an easier way, to a) get the holes selected and b) create a black N white image of them.

You look at the alpha channel, and it LOOKS like the BlackNWhite image I need, but it isn't.

Which is agravating.

I just hope someone knows the answer.

 I hope this helps and I'm understanding just what your trying to do..

 Schurby

Well yes, partly Schurby, and thanks for replying.

Yes, I'm with you as far as your 3rd image above, but I need a jpg that looks like your 1st image - the black and white one - I need this as well as getting to your 3rd image because I need that blackN white image to drive the transparency in Bryce.

So how can I save that alpha image as a blackNWhite jpg?

(By the way, did you make that grid or is it from a photo? - if you made it, how did you make it?)

Go to your channels tab, and click on the eye to the left of all channels but the alpha channel you created. With your alpha now visible, do a ctrl-A, ctrl-C to copy the alpha.

Go to your layers tab, create a new layer, and ctrl-V to paste the copied alpha into a layer. You can now just do a save as... and select jpg.  Don't worry about hurting your current layers -- photoshop will return to the layers as soon as the jpg is saved. You now have the alpha saved as a jpg and you can delete the copied layer in your document if you no longer need it.

Don't forget to turn your alpha channel off and make sure your color channels are turned back on after you are done.

I see now what you want, the alpha map itself for Bryce or any other 3d program. The above explanation is exactly how I would do it. I wasn't sure at what you were trying to achieve, but I use fivecat's method all the time for alpha maps.

  Schurby

Quote - There are several ways to do this, but I will tell you one that I think is easiest to describe and for you to understand.

Go to your channels tab, and click on the eye to the left of all channels but the alpha channel you created. With your alpha now visible, do a ctrl-A, ctrl-C to copy the alpha.

Go to your layers tab, create a new layer, and ctrl-V to paste the copied alpha into a layer. You can now just do a save as... and select jpg.  Don't worry about hurting your current layers -- photoshop will return to the layers as soon as the jpg is saved. You now have the alpha saved as a jpg and you can delete the copied layer in your document if you no longer need it.

Don't forget to turn your alpha channel off and make sure your color channels are turned back on after you are done.

Ah thanks. It was ctrl A that I was missing - I usually do that by using the rectangular selection tool and draw the box around the entire canvas - that's just the method I've used up to now, but if I can only remember it, ctrl A is certainly quicker.

However I notice that this method gives me black hole areas that are slightly smaller than I need - ( I did this myself by using the stored selection of holes that I had already expanded by 1 pixel (and fiddling with reducing feathering etc etc, so not quick) and using the fill bucket tool to flood fill the holes with black - adding a layer beneath the holes layer, filled with white and then merging these 2 layers gave me the jpg result - black holes on a white ground)

But that's a bit long winded and I was too tired last night to have that fully in my head, I had an inkling but my brain wasn't working too well. Lol!

I'm not sure... maybe the alpha method you describe would in fact be good enough, since you probably wouldn't be looking too closely at the grid... or would you?  Hmmm I'll have to think about that.

Well now I have both I guess the thing to do would be to try both as transmaps in Bryce.

I guess that means I need to go do that.

Quote - I see now what you want, the alpha map itself for Bryce or any other 3d program. The above explanation is exactly how I would do it. I wasn't sure at what you were trying to achieve, but I use fivecat's method all the time for alpha maps.

  Schurby

Yes, probably my fault, as I can get a bit involved when trying to explain what I'm trying to achieve, especially when you aren't sure if you actually need what you think you do to get to the end point.

I think I have a problem with this simply because when I used the save selection method (without adjusting the selection first) I found that I had a nasty ghostly gap between selections and that worried me:

See image:

This shows the difference between the selection of the holes and the selection of the inverse of the holes (I flooded both with black to show the gap between the two selections - not very accurate I thought, looked like some sort of feathering of the selection I thought, so I was trying to solve that with the expanding of the selections so as to close that gap between the two.

Is there some way to turn feathering off on selections?  Maybe if there is, that would help?

S'okay, I found out how to turn off feathering.

And I've now got the grid correctly mapped with the correct alpha, in this case I'm using a .png to drive the alpha channel.  And I've managed a nice little demo animation - just to see what the model looks like with the grid opening.

Thanks for all the help on this.

Another option that works well for me is using "Selet/Color Range", there you can adjust the fuzziness of the selection manually. If there are still artifacts, I hit the quick mask button at the bottom of the tool panel, zoom in, brush out what I don't want with a NEG(black brush), click back on the Quickmask button and voila, the selection is precise.

Rod,

Hmmm, I've used select colour range often myself, but you seem to have an added dimension there with the zoom in, zoom out, NEG Black brush and so on that maybe you should make a little video tut for this sort of stuff.  Could be useful!

When my selection isn't precise (usually!) I just use the freehand selection tool to remove and add to the selection until it is precise.  I sit with my wacom pen in one hand and my other hand hovers over the Shift and Alt keys - for adding and removing as I draw around (most recently) a lily.

Although I often find that it's quicker to draw roughly around the lily and then zoom in for precision, rather than starting with the colour select option.

Colour select sometimes selects an awful lot of teany tiny dots scattered all over the image - which can be a mess to sort out.

If I may chime in on Rod’s suggestion…the Quickmask is easily accessible by simply pressing the “Q” keyboard key. And by having your foreground and background colors set to the default Black & White which is easily attainable by simply pressing the “D” keyboard key one can alternate between adding to the quickmask selection or subtracting from it by pressing the “X” keyboard key to alternate between the foreground and background colors. Just a quick tip.

Also, you can select the RGB channels which offer different degrees of contrast (the red channel often having the most contrast) to select portions of your image. And these can be further refined by using different filters such as High Pass or from Image Adjustments Threshold to increase contrast.

Yes, I've used channels before, but I hadn't thought of using them to select more of a single colour like that for brushes... I'll have to try that.

Haven't used HighPass filter before, but I've been reading about it recently in a book I got from the library on PhotoShop CS4.  Never even heard of Image Adjustments Threshold, apart from just seeing it under the Image Adjustments list.