Creating a mask from a black pixel selection/pixel layer (with alpha) - I found an Inconsistency

[oliver_fuchs]

Hi,

First of all, congratulations on the new version 2.3 - again very successful!

There are different ways to create a mask! But the way to create a mask has some inconsistency:

1) I do a selection from a pixel-layer. Then I choose refine. For the output I choose Mask (Mask — applies the refinement to the selection as a mask). OK - and the Refine Selection is doing it right if the selected part was pure black - it creates an inverted mask (because otherwise it would be black in black - so it turns the black-selection into white - and the rest into black).

2) If you have a black pixel layer (with alpha) and then do in the layers panel Rasterize to a Mask - the black part will be black and you end up with a complete "black mask" - this step is not doing the conversion like it is done in the refine selection. You first have to invert the black pixel layer - then you get a mask - that you have to invert again.

3) The third way to do it right would be to select the pixel layer and choose Edit - Matte. Then you can rasterize the Matte to a mask!

mask_layer.afphoto

[NotMyFault]

1 hour ago, oliver_fuchs said:

2) If you have a black pixel layer (with alpha) and then do in the layers panel Rasterize to a Mask - the black part will be black and you end up with a complete "black mask" - this step is not doing the conversion like it is done in the refine selection. You first have to invert the black pixel layer - then you get a mask - that you have to invert again.

When you use rasterize to mask, only the color of pixels will be used.

transparent areas will be counted as black color, despite transparency is shown as white by default (transparent canvas setting off).

You can see the actual color by using channels panel, and choose one color channel to be visible (but not alpha).

 

[oliver_fuchs]

Hi,

ok ... document is set to transparent background - the object of desire (the thing that should get a mask) is pure evil black. Then the three methods of creating a mask are handling the black object different!

The problem was that I had this black picture and wanted to turn that layer into a mask with rasterizing the layer to a mask - and the result was a pure black screen! Until I realized that the "rasterize to mask" is not inverting a black object before rasterizing while the selection-refine-output mask will do this!

 

Oliver

 

 

 

[NotMyFault]

25 minutes ago, oliver_fuchs said:

Then the three methods of creating a mask are handling the black object different!

Yes, intentionally.

You can create a mask based on either color values, or transparency values. 

[oliver_fuchs]

Hi,

 

ok ... let me see that I understand it correct ... so that means that "rasterize to a mask" grounds on color values. Ah - now I see your point. BUT - in that case the program is producing a wrong result ... it keeps the black and then cannot make the difference anymore between what is black as a color and what is black form the generated mask ... am I right or am I wrong? So you cannot build a mask on a black object when using the rasterize a mask option? Ah - they should change this or add something like in the painting mode "protect alpha" but as "protect black objects"!!!

Thanks

Oliver

[NotMyFault]

I don’t fully get what problem you see.

if you rasterize a pixel layer to mask, black is treated as black, no matter if it comes from from the pixel layer colors or implicitly from background.

the color values are transformed into alpha values. Areas already transparent in the source layer stay transparent in the mask. It is irrelevant what color the canvas, background or any layers below show.

[NotMyFault]

12 minutes ago, oliver_fuchs said:

So you cannot build a mask on a black object when using the rasterize a mask option?

A black object will create a mask where nothing is visible when using rasterize to mask.

[NotMyFault]

It seem you are still mixing 2 ways of creating a mask:

• selection from layer: will use only the alpha channel to create a selection, and ignore color values. When creating a mask while this selection is active, you essentially copy the alpha channel.
• rasterize to mask: converts the color values into alpha values. Ignores the alpha channel, except when alpha is zero colors will be forced zero, too.

https://affinity.help/photo2/en-US.lproj/pages/Selections/selections_fromlayers.html

[oliver_fuchs]

Hi,

ok. ... I do understand this. What was missleading here is the definition of rasterise in the manual: If you rasterise a shape it becomes a pixel layer. It has a clear form ... it has an inside and and outside part. So you also rasterise the shape to a mask ... and I always thought that the main result of this mask is the pure shape - I need a circle maks to hide round parts in my image (or to show them). And I understood the manual in that way that you use " rasterise to a mask" only for shapes! So I thought Affinity takes the black pixel layer like in the example above and rastrises it to a shape equal to the shape of my pixel layer! I thought the result would be the same as in  building a mask from a selection - pure black and white mask! But it dos not. That was my problem! I was missreading the manual!

 

Oliver