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Alpha Control

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QueJet
Alpha Control
on May 23, 2007 at 9:41:45 am

Are there any plugins, or really anything, that would give me more control over the alpha channel of layers in photoshop? As it stands it is very difficult to adjust this. The best solution I've come up with is to duplicate the layer on top of itself and merge down, and that can be problematic at times.

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Darby Edelen (wuzelwazel)
Re: Alpha Control
on May 23, 2007 at 3:08:23 pm

[QueJet] "Are there any plugins, or really anything, that would give me more control over the alpha channel of layers in photoshop?"

What kind of control are you looking for? You can access Alpha Channels in the layers pallete's "Channels" tab.

Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA


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QueJet
Re: Alpha Control
on May 23, 2007 at 5:52:49 pm

[Darby Edelen (wuzelwazel)] "What kind of control are you looking for? You can access Alpha Channels in the layers pallete's "Channels" tab."

wow you had me worried there. I thought I missed something amazingly obvious.

OK to better explain what I want I feel I should clarify terms (whether these terms are technically right isn't important, it's just so were on the same page). I have some 24 bit PNG images. They are in these formats because PNG-24 offers lossless compression with 4 channels. (and i think full 8 bit). The images have RGB channels and an ALPHA channel. (oh these are strait images, not pre-multiplied) Now I could take this image into after effects, and I have several options where I could raise the alpha channels values.

Now what if i import this layer into photoshop. Now i have the image, alpha channel and all in the layer, but what if i want to raise that alpha channel, or make the alpha channel for that layer to be 255 or 0? As it stands the only way I know of modifying this channel in this sense is to duplicate the layer on top of itself, if thats not enough i'll duplicate several times, merge down, then duplicate several more times.

This is not a good approach by any stretch of the imagination. Ive even seen my color data start to freak out when I've done this enough times before. And for 32 bit HDR images on a 2048*2048 canvas? I don't have NEARLY the processor strength to make that road worth travelling down. As far as I know, photoshop has no native tools to modify the alpha channel of a layer. So are there any plugins or anything I can use to overcome this?

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Darby Edelen (wuzelwazel)
Re: Alpha Control
on May 23, 2007 at 8:17:00 pm

[QueJet] "Now what if i import this layer into photoshop. Now i have the image, alpha channel and all in the layer, but what if i want to raise that alpha channel, or make the alpha channel for that layer to be 255 or 0? As it stands the only way I know of modifying this channel in this sense is to duplicate the layer on top of itself, if thats not enough i'll duplicate several times, merge down, then duplicate several more times."

You can edit the Alpha Channel just like any other grayscale layer in Photoshop in the "Channels" tab I mentioned earlier. You can apply Levels adjustments, blurs, spatter, noise, or anything else you can do in grayscale. Just select the alpha channel, make it visible and do what you want to do =)

I think the problem is your use of PNG. I can't seem to find anyway to save a PNG out of Photoshop with RGB + Alpha. PNG-24 can be saved from the Save for Web option, but I still can't seem to get it to preserve an alpha channel. It looks to me as though PNG-24 doesn't save an alpha channel but does save transparency. Note: If you are seeing transparency in the RGB channels of Photoshop then you are actually not dealing with an Alpha Channel. Photoshop does not translate alpha channels directly into transparency information as After Effects does.

You can use a number of common formats that support an alpha channel, including: TIFF, PICT, TGA, BMP and PSD. I wouldn't recommend using PNG. You can save losslessly with any of the aforementioned formats (most of them even have lossless compression).

Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA


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QueJet
Re: Alpha Control
on May 23, 2007 at 9:27:02 pm

ugh. I'm doing my very best to communicate the problem. Let me be clear: When i say alpha. I don't mean go into the channels tab and hit new channel. That channel isn't ACTUALLY ALPHA!
[Darby Edelen (wuzelwazel)] "Photoshop does not translate alpha channels directly into transparency information as After Effects does."
See this is where the confusion is coming from. This is the root.
Photoshop DOES! But you have no control over it.

I don't think you believe me though, so I direct you to this wiki page that explains the alpha channel and its use in images in more detail.
http://en.wikipedia.org/wiki/RGBA_color_space
Also: Alpha compositing:
alpha compositing is the process of combining an image with a background to create the appearance of partial transparency. It is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image in a process called compositing.
~ wiki

When your clicking the new channel button in the channels tab, your only making a spare channel, which is later interpreted as the alpha channel when you save in some image formats. That's not actually alpha
What I'm looking for is control over my images alpha, while I'm alpha compositing.

Remember: I'm not opening the images directly. I'm creating a new canvase, and then pasting these images over.
Here is an example of a 24 bit

as you can clearly see, this image has an alpha channel! Your browser (if you have it up to date) Is compositing this image on the background of this website, in this case white, but if you were to load this image into photoshop, you wouldn't get a white background!

neet huh?




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Darby Edelen (wuzelwazel)
Re: Alpha Control
on May 24, 2007 at 5:12:35 pm

[QueJet] "Let me be clear: When i say alpha. I don't mean go into the channels tab and hit new channel. That channel isn't ACTUALLY ALPHA!"

But that is where Alpha channels will appear when Photoshop reads them. If Photoshop isn't able to read the Alpha out of a PNG-24 as anything but transparency then that doesn't change the fact that you shouldn't be using a PNG-24 if you want control over Alpha in Photoshop.

I appreciate your desire to be perfectly clear, but you shouldn't be so stubborn as to ignore the fact that the semantics you're presenting here haven't changed the fact that Targas, TIFFs, PICTs, and PSDs will preserve the Alpha Channel when saved with the 'Alpha Channels' checkbox marked.

I can understand using a PNG-24 if you're working for the web, otherwise I can't understand why you want to use it.

Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA


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QueJet
Re: Alpha Control
on May 25, 2007 at 2:02:49 am

because i have no choice! This is the format the media I'm using outputs in, i can't convert it. But more importantly, its not about controlling the alpha of the output! Its about controlling the alpha of the input. I need that control... badly. I can't simply tell where I'm getting my media from to export in a different format. It's just not possible!

I know what the solution to my question is likely to be some kind of third party plugin that allows me to have more control over the transparency of my layers. This is what I'm asking for.
Really it's not stubbornness. It's necessity.

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Darby Edelen (wuzelwazel)
Re: Alpha Control
on May 25, 2007 at 4:51:40 pm

[QueJet] "I can't simply tell where I'm getting my media from to export in a different format."

So I'm guessing you're not working with an external program that's dumping PNGs but that you're actually getting them from a source entirely removed from yourself?

If you're forced to work with PNGs then I'd first look to see if what you want to accomplish is feasible in AE. I don't know the specifics of what you're trying to do, but there are definitely ways to get at the alpha and modify it in AE. Ranging from the simple (Channels > Alpha Levels) to the complex.

Otherwise you could export your PNG (or PNG sequence) out of AE to a different format with an alpha that Photoshop can edit. Try adding the sequence or image (use save frame as) to the render queue and setting it to Photoshop Sequence, or TIFF sequence, or Targa Sequence. Then in format options make it Straight (Unmatted) and export RGB+Alpha.

These files will look strange in Photoshop as the alpha won't be interpreted as transparency, but you'll have your editable alpha channel in the channels tab. If you want to preview the transparency as it will appear in another program (AE for example) you can make a selection based on the alpha (ctrl/cmd click) duplicate your background and use Layer > Layer Mask > Reveal Selection.

These are workarounds, ideally you wouldn't be limited to PNG-24. Remember your adjustments to the alpha will be limited by the amount of information in the RGB channels.

Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA


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QueJet
Re: Alpha Control
on May 23, 2007 at 9:36:26 pm

Wait hang on, I'd like to tag on one last image just to make sure everything crystal clear. Here is the same image in photoshop, with 3 layers using the very same alpha channel, the first layer had the brush strokes, the second layer has a black and a white gradient, and the third has a imported PNG file.


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ekim wahs
Re: Alpha Control
on May 23, 2007 at 3:58:48 pm

Are you looking to create straight(unmatted), or premultiplied alpha channels based on transparency? If so in CS3 you can use File/Export/Render Video to render still image formats that support transparency with Alpha options for Straight, Premultiplied with white, black, or a custom color.


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Victor Angry
Re: Alpha Control
on May 27, 2007 at 6:19:53 pm

Google for "photofreebies". There is a filter called "remove transparency" which will take every pixel in your layer/selection and make it fully opaque.

You could also use Telegraphics Filter Foundry (also free) and just use "a=255" as your script.

If you're on Mac you'll have to go the FF route as photofreebies as compiled for Windows only.


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Alejandro Martinez
Re: Alpha Control
on Oct 24, 2012 at 4:54:35 pm

(Reviving this mega-old thread)

It is just impossible, let alone communicate the problem :(...
For example, suppose you use a soft brush with white color, put some soft spots on the screen... but then later you want to boost it or contrast it with a "Levels..." adjustment layer (with ctrl+alt+g, so it only modifies the said layer with the soft spots).
It will do NOTHING because for the the layer it is modifying is fully white, the histogram only has one spike at the white section of the spectrum.
OF COURSE there is an alpha channel embedded in that layer, the layer is not 100% white, it's a bit transparent at some places and no, it won't appear ever on the Alpha Channel (at the Channels section).

After effects solves this by allowing a "Levels Adjusment" selector of what to modify (R,G,B, RGB, Alpha, etc).

Has anybody found a way around this? the solution is always about duplicating - merging, putting a black background - merging - adjusting that - using the result as a mask (!). What about modifying a bit once again? Well, repeat all that until the layer and colors and banding just makes it useless.

(Rant over, sorry for that)


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