Preserved Topic: Two quick rambles

Some time ago I went on two rambles over at PSG. Finally getting off my lazy ass and posting them here. Besides, it's been awhile since I went on a ramble in these parts.

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Upping Opacity

I love using Edit > Fill with Mode: Behind.
101 Uses

But it doesn't always work. Like on photos when you need to bring the opacity of individual pixels in a layer up to 100% while mantaining the colour data.

Grab a photo. Grab Eraser tool, make it big and soft, and give the photo a few strokes. You know have some partial transparency in the photo.

Now, the pixels in the photo's layer have two different types of data: colour and opacity. Let's say you want to get those partially transparent pixel's opacity back up to 100% with their original colours. Well, Fill Behind just won't work because it uses a solid colour. Doh!

The fix? Simple enough.

Copy the layer
Merge down (ctrl + e)
Rinse
Repeat

The lowest % opacity pixel will basically tell you how many times to copy. Or you could just eyeball it, which is no big deal.

This trick has saved my posterior a few times.

The down side:
When a pixel reaches Opacity: 0 (Transparency: 100%), the colour information is tossed. That has Suck Factor: 115%.

The complete fix?
Use a Layer Mask! Some people don't, and dealing with it can be a pain. Hopefully you'll never have to deal with it. In case you do, the above trick should fix things (with the exception of 100% transparent pixels, which is another story all-together).

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If you *must* be destructive

I remember when Extract and the New & Improved Eraser Tools were introduced. People running all over the place shouting nothing but good things.

They are good, but they are destructive. Once a chunk of a subject is gone, it's gone.

Ah, but the Eraser Tools allow you to do some pretty creative extraction things that aren't really available else where in PS. They are good for some things.

The Fix Part 1:
Use the Eraser tools or Extract on a copy. Most people I know already do this, but I have seen some "mundanes" out there. Not pretty. Of course, Undo (ctrl + z) is a good friend when you don't quite have the hang of the various parameters. History palette is always a life saver.

The Fix Part 2:
Use a Layer Mask anyways.
What?!
Follow me:
1) Copy.
2) Extract using Extract or Eraser Tools.
3) Load the selection (ctrl + click).
4) Back to original copy.
5) Add Layer Mask.
6) Trashing destructed layer optional.

Best of both worlds. You can use the fancy-smancy tools and remain non-destructive.

I've suggested this several times and I usually get one of two reactions:
1) Duh! as in, "That's sooo obvious. If you can't figure this out, exit PS and return your computer."
2) Doh! as in, "Why didn't I think of that? If I had known sooner, I could have saved myself a headache or two."

play.fiddle.learn

If Photoshop merely accepted the fact that transparency is a channel just like red, green, and blue are, then this would be incredibly easy: just go edit the transparency channel. It's ridiculous how Photoshop hides the fact that transparency and color channels are exactly the same type of information.

[This message has been edited by Slime (edited 01-10-2003).]

i think that's quite a valid point there slime.

...and thanks for sharing, wj.

but what's this extract stuff? i my knowledge of ps has some pretty big chunks missing, methinks.

reitsma: It should be Image -> Extract.

Not sure though. I'm probably way off, as it's been a while since I used the command

[This message has been edited by Raptor (edited 01-10-2003).]

Slime, maybe write a wee message to the good people at adobe. Theres a place on their site that lets you post feed back and recommendations. I sent them a few about two years ago , one of which I wrote they should make an image browser, and they did. I doubt it was my suggestion that sparked that off, but making the transparency function the same as R,G+B is a very good idea.

oh and warjournal thanks for the tips of course !!

Thanks to warjournals general permission to put his writings into the faq (give yours today),
I put it into the faq:

:FAQ:

:FAQ:

thank you,
warjournal.

So long,

Tyberius Prime

[Emp edit: Sorry couldn't resist the tempatation to turn them into FAQ pointers ]

[This message has been edited by Emperor (edited 01-10-2003).]

1) Duh.

If it's not asking too much can I see a picture of before and after to see what kinda effect is happening here. Everytime I try it I get a visual mess. I don't think I understand what is going on with this one.
Thanks

A wise man once said;
"I don't know!?!?"

MFS, there really aren't any before and after pics. These are ways of working and/or ways to save your ass.

Slime, I've been thinking about what you said. However, I don't think it's implementable. If it can be done, and I'm sure it can, how would it work?

Let's say I wanted to erase something and paint over it. How would that work?

With the thought that I've put into it, it sounds like more work than the Eraser and Layer Mask as they are right now. Know what I mean?

I'll admit that I'm a tad lost on this, so it might actually be easier than what I'm imagining.

"Slime, I've been thinking about what you said. However, I don't think it's implementable. If it can be done, and I'm sure it can, how would it work?"

Ideally, the alpha channel would appear just below the "blue" channel in the channels box. A layer would be constructed visually by pulling out the red, green, and blue color information, and then averaging that with whatever's below the layer with a weight defined by the alpha channel.

"Let's say I wanted to erase something and paint over it. How would that work?"

The eraser is a tool that only affects the alpha channel. As you erased, the alpha channel would change. The colors would *not* change (unless this was a Background layer or something silly like that). Wherever you dragged the eraser would have the same effect as drawing with a black airbrush on the alpha channel. It makes things transparent, but the color remains the same.

The paintbrush/airbrush is a tool that affects all channels. When it's applied to part of the image, it (a) makes pixels around it less transparent (makes that part of the alpha channel closer to white), and (b) changes the colors around it to be closer to the color you're painting. How much it changes each pixel is a complicated function of the radius and of the current color (red,green,blue,alpha) of each given pixel.

This is actually how it is already internally implemented. They just hide the alpha channel as though it's some magical thing, so you always have to deal with it separately. The eraser and layer masks would certainly stay; layer masks are actually nothing more than an extra channel which is multiplied by the alpha channel to create a new alpha channel, and erasers are a shortcut for painting only on the alpha channel. They're very useful. But there are times when you just can't beat 100% direct access to the channel you're working with.

While we're talking about problems with Photoshop, I'd also like to complain about the lack of an "additive" blend mode. Addition is found *everywhere* in nature. Fire, reflections, highlights, everything - it's all the addition of separate colors of light. Amazing things could be done with an additive blend mode. Sigh.

Of course, while they're at it, I'd also like division and subtraction (not their silly "absolute value of the subtraction" thing they've got called "difference"). Then you could have some *real* power. (However, for these to really be effective, you'd need to be working in at least 16 bits, and have the ability to have negative values, the former of which isn't well integrated yet and the latter of which probably never will be implemented at all.)

But that's just me as a mathematician =)