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How to Edit the Alpha Channel

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8 hours ago, protoloss said:

And by the way: All the 2D illustration and painting packages I have used so far (except for PS) work similar to AP. If you want to create a mask or transparency in other packages, you have to erase in the mask. Photoshop is the only software that allows you to use black and white directly in the alpha channel. I think, when they started designing AP/AD they went with what everyone else outside of Photoshop does: Erase and paint in the alpha channel.

Maybe that is one of the reasons Photoshop is so much better than any other application to work with Alphas.

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11 hours ago, protoloss said:

All the 2D illustration and painting packages I have used so far (except for PS) work similar to AP. If you want to create a mask or transparency in other packages, you have to erase in the mask. Photoshop is the only software that allows you to use black and white directly in the alpha channel.

Corel PhotoPaint has a mode where you can paint in greyscale (black, white, or in between) on a mask or channel layer.

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30 minutes ago, sfriedberg said:

Corel PhotoPaint has a mode where you can paint in greyscale (black, white, or in between) on a mask or channel layer.

So do the Affinity apps.


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On 6/26/2020 at 8:49 PM, rui_mac said:

Please, someone tell me what are the advantages of having "achromatic (colorless)" alphas instead of grayscale alphas.

None - grayscale and achromatic are synonymous, so I don't know why R C-R made such a distinction.

Some people (not you), get confused between the visualisation of data and the actual data itself.

(As you already realise) a single-channel raster image, one of the colour channels of a multi-channel raster image, an alpha channel, a "spare channel", a pixel mask and a pixel selection are all the same - a 2D matrix of numbers - and there is no intrinsic reason that they cannot be manipulated with the same tools and functions when a software developer chooses to facilitate that capability.

 

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47 minutes ago, anon2 said:

None - grayscale and achromatic are synonymous, so I don't know why R C-R made such a distinction.

Not to put too fine a point on it but they are not entirely synonymous. At least as defined here, an achromatic color is one that lacks hue. Achromatic colors, a.k.a. "achromatic grays" (IOW, blacks, whites, & greys) can exist in any color space, including RGB & LAB. Grayscale is a color space that contains only intensity, not hue.


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22 minutes ago, R C-R said:

Not to put too fine a point on it but they are not entirely synonymous. At least as defined here, an achromatic color is one that lacks hue. Achromatic colors, a.k.a. "achromatic grays" (IOW, blacks, whites, & greys) can exist in any color space, including RGB & LAB. Grayscale is a color space that contains only intensity, not hue.

LOL! Here we ago with the your usual attempt at obfuscating the fact that you wrote nonsense earlier.

Your cherry-picked distinctions are meaningless in the context of an alpha channel. An alpha channel can be visualised as a greyscale/achromatic image, but that's not what it is.

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Just now, anon2 said:

Your cherry-picked definitions are meaningless in the context of an alpha channel.

How so? As you said, Affinity only supports alpha transparency channels. Isn't that the context we are discussing here?


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It doesn't matter really what you call them, masks and each R G B and A channels or whatever other channel should really be treated the same IMO and you could be able to edit them all on an individual basis with the regular tools in the application. Make selections, paint from black to white and anything in between, copy/paste etc. and the process of exporting should be maybe more open ended for the users to choose how things are exported. I understand each file format has very unique features though but editing the basic RGBA shouldn't be complicated, difficult or confusing.

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2 hours ago, anon2 said:

Now you are confused about who wrote what:

@rui_mac wrote "Alphas ARE greyscale images." Alpha transparency channels are not greyscale images. They do not have a grey or any other color component. If a transparency mask is painted on there is no grey or any other shade of paint being applied to it. "Grey" refers to a range of colors, those with no hue, sometimes referred to as achromatic in the literature. It does not refer to the opacity of anything. That would be absurd, like saying that a pair of light grey pants are mostly transparent.


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7 minutes ago, R C-R said:

@rui_mac wrote "Alphas ARE greyscale images." Alpha transparency channels are not greyscale images. They do not have a grey or any other color component. If a transparency mask is painted on there is no grey or any other shade of paint being applied to it. "Grey" refers to a range of colors, those with no hue, sometimes referred to as achromatic in the literature. It does not refer to the opacity of anything. That would be absurd, like saying that a pair of light grey pants are mostly transparent.

Look, stop these infantile games! You said that I wrote a specific phrase, when you were the one who actually wrote it. I posted proof of that and now you are responding with a quote of someone else's words. Be an adult and accept that you made a mistake. If your bizarre states of confusion in forum threads is a health problem, please accept my apologies for being so harsh.

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1 minute ago, anon2 said:

You said that I wrote a specific phrase, when you were the one who actually wrote it.

I did not mention any specific phrase written by you, only that like I thought you were trying to say, that Affinity only supports alpha transparency channels -- IOW, that this alpha channel is spatially a 2 dimensional array of numeric values that is single valued at any point in that array, in the same way that R, G, or B channels are in an RGBA image.

I think making this distinction is important because I agree with everyone that it would be better if Affinity allowed us to treat these arrays as if they were greyscale images (even though they are not) so we could edit them with all the same tools we can use with real greyscale images.


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1 hour ago, R C-R said:

@rui_mac wrote "Alphas ARE greyscale images." Alpha transparency channels are not greyscale images. They do not have a grey or any other color component. If a transparency mask is painted on there is no grey or any other shade of paint being applied to it. "Grey" refers to a range of colors, those with no hue, sometimes referred to as achromatic in the literature. It does not refer to the opacity of anything. That would be absurd, like saying that a pair of light grey pants are mostly transparent.

If the nomenclature is so important, then...

Greyscale images, alpha channels, color component channels, transparency maps, etc, ARE ALL A MATRIX OF VALUES, as in... a long list of 8 bit or 16 bit numbers.
So, all operations that can be done with one, should be possible with all others.
Are you telling me that a transparency map is not a list of values?

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9 minutes ago, rui_mac said:

Are you telling me that a transparency map is not a list of values?

No, of course not. I'm just pointing out that alpha channels & images (greyscale or otherwise) are not the same thing.


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5 minutes ago, R C-R said:

No, of course not. I'm just pointing out that alpha channels & images (greyscale or otherwise) are not the same thing.

Internally, aren't they the same? Just a list of values!
If they are (and they are), there is no reason for us to not be able to manipulate an alpha channel as a greyscale image.

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 I think we all agree on that channel editing needs to improve in Affinity. Just image you could select a b/w layer and then copy paste it into all channels! This thread non existing because it just works! No hate, no nitpicking! Just love and happy accidents in the alpha channel.... Have a nice weekend guys!

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4 hours ago, rui_mac said:

Internally, aren't they the same? Just a list of values!

I do not know how they are stored internally in the native Affinity file format but as I understand it channels consist of a list of single values (the A channel values) while greyscale images consist of a list of value pairs (one for intensity & the other for alpha transparency).

I believe this is why in Affinity Photo, for a Gray/8 or Gray/16 document, the Procedural Texture filter equations can be applied only to two channels (& why it is considered a bug that in the live version of that filter there are 4 channels).


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16 hours ago, R C-R said:

I do not know how they are stored internally in the native Affinity file format but as I understand it channels consist of a list of single values (the A channel values) while greyscale images consist of a list of value pairs (one for intensity & the other for alpha transparency).

I believe this is why in Affinity Photo, for a Gray/8 or Gray/16 document, the Procedural Texture filter equations can be applied only to two channels (& why it is considered a bug that in the live version of that filter there are 4 channels).

The greyscale values are just a single list of values.
A "greyscale LAYER" includes the greyscale list of values and a n opacity list of values.
All layers include an additional list of values for the opacity.

So, a greyscale LAYER is simple a set of two "greyscale" lists.
And an RGB LAYER is a set of four greyscale lists, one for Red, one for Green, one for Blue and one for opacity.

Once again, there is no excuse for the opacity list (call it alpha, or key, or mask, or opacity map, or whatever) that is merely a list of values just like a greyscale image or any of the composite channels of an RGB or CMYK image, to be treated differently.
In a nutshell, an alpha channel is exactly the same as a greyscale image and should be treated the same way, allowing all tools and operation that a greyscale image allows.

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On 6/27/2020 at 10:17 AM, R C-R said:

Not to put too fine a point on it but they are not entirely synonymous. At least as defined here, an achromatic color is one that lacks hue. Achromatic colors, a.k.a. "achromatic grays" (IOW, blacks, whites, & greys) can exist in any color space, including RGB & LAB. Grayscale is a color space that contains only intensity, not hue.

If you pay so much attention to definition details, what would you say that the individual channels of an RGB image are? Chromatic? Or achromatic?
Because each individual channel has no color information. It just contains a list of values that define the intensity of each individual component.
Just like a greyscale image is just a list of values that define the intensity of light of each pixel.
Just like an alpha is just a list of values that define the opacity of each pixel.
If they are all the same (and stored the same way, internally), why can't you perform on an alpha channel the same operations that we can perform on a greyscale?

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21 minutes ago, rui_mac said:

So, a greyscale LAYER is simple a set of two "greyscale" lists.

Nope. In a greyscale document, it is a single list of two paired channel values that together define the intensity & opacity of any point in that layer object.


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29 minutes ago, R C-R said:

Nope. In a greyscale document, it is a single list of two paired channel values that together define the intensity & opacity of any point in that layer object.

You've reverse-engineered the Affinity document structure? Or have you some other proof?

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53 minutes ago, R C-R said:

Nope. In a greyscale document, it is a single list of two paired channel values that together define the intensity & opacity of any point in that layer object.

Do you know how the data structure is stored? Is it a list [witdth, height, 2] matrix or two [width, height] matrixes?
And, no matter how they are stored, they are two matrixes with the same structure, containing the same data type values.
So, once again, there is no excuse for not being able to perform the same operations on a "opacity map" matrix that can be performed on a "greyscale" matrix.

I'm a coder and I know what I'm talking about. One of the last plugins I coded as a 3D vertex painting set of tools. It deals with RGB and, optionally, with an opacity map. The same set of code that is used for each of the R, G and B channels (that are, fundamentally, three greyscale channels), is the one I also use for the opacity map.
I even coded Dodge, Burn and Blur tools and they work the same at the RGB level as they work at the opacity level.

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On 6/27/2020 at 3:21 PM, R C-R said:

That would be absurd, like saying that a pair of light grey pants are mostly transparent.

That's the reason why in particular young people don't wear grey? 😅
Nevertheless an interesting comparison if you consider that a white fabric or paper occurs is more translucent than a black one. 😉


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5 hours ago, anon2 said:

You've reverse-engineered the Affinity document structure?

Nope. I already said that I do not know how they are stored in the native file format. As I also said, I am just going by what the Procedural Texture filter equations expose to the user.


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19 minutes ago, R C-R said:

Nope. I already said that I do not know how they are stored in the native file format.

Yes I know you don't know, LOL. So now try to explain why you told rui_mac that he was wrong? Oh wait! Let me guess. You read something in Wikipedia and jumped to a quite probably wrong conclusion because you are ignorant of other possibilities that would be known to anyone with a background in developing image processing software. There is a very high probability that rui_mac was correct, in case you haven't yet grasped that.

34 minutes ago, R C-R said:

As I also said, I am just going by what the Procedural Texture filter equations expose to the user.

But that provides no clue to the Affinity document structure.

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