[Photo] How to draw directly in Alpha-channel?

[Friksel]

Hi,

I'd like to draw directly into the Alpha channel of a layer. I did this in the past in Photoshop and I'm positive this must be possible in Affinity too as there are switchable channels per layer with an edit button behind each channel.

But for some reason it's not painting inside the channel with a paint brush tool (it seems to paint in the R/G/B channels still.

How can we paint black/white/grayscale directly into the Alpha channel (not in the r/g/b channels) in Photo?

[Lisbon]

Hi Friksel

See if this workaround works for you.

Rasterise to mask a white pixel layer Add a mask and drag it to the top. Paint on the mask.

If you want to see only the alpha channel, turn off the visibility of the RGB channels.

At the end you can merge the mask (Ctrl+E) (destructive)

[Friksel]

34 minutes ago, Lisbon said:

See if this workaround works for you.

You mean you think it's not possible to draw directly on the Alpha channel? Than what is the channels tab for?

I'm pretty sure those edit-icons (the pencil icon) aren't there by accident, right?

 

This is what the Photo manual says about channels, so I would definitely expect the Alpha channel to be drawable:

[joe_l]

1 hour ago, Friksel said:

it's not painting inside the channel with a paint brush tool

You can "paint" with the Erase Brush Tool ... if this is what you are looking for?

[Friksel]

15 minutes ago, joe_l said:

You can "paint" with the Erase Brush Tool ... if this is what you are looking for?

Sorry, that's not what I want. I want complete paint-control over the grayscale Alpha channel.

I see now that the alpha channel is working completely different than in Photoshop. Affinity Photo doesn't let us paint directly into a channel, but let us paint in a LAYER and let us turn off channels to paint on. So we always seem to be painting on the RGB channels and the alpha channel got created automatically, instead of letting us paint on the alpha channel.

So we can indeed use the eraser to erase pixels from the RGB channels, which automatically erases the same pixels in the alpha channel, but I need semi transparent painting of pixels directly into the alpha channel and that's not possible this way. Beats me why Affinity created this totally different workflow compared to Photoshop.

BTW it seems like the info in the help doc isn't completely right either; it tells us FOR EACH CHANNEL we can fill the CHANNEL information. But that doesn't seem to be true?!

Guess painting into the alpha channel is just impossible in Affinity. Which makes me a little sad.

Will try the workaround as mentioned by @Lisbon now. Thanks @Lisbon.

Just found this thread on the forum with more people having complaints about it:

 

[Lisbon]

28 minutes ago, Friksel said:

I'm pretty sure those edit-icons (the pencil icon) aren't there by accident, right?

Right.
There must be many examples but try to invert (Ctrl+I) just the red channel. You will need those edit buttons.

[Lisbon]

8 minutes ago, Friksel said:

I want complete paint-control over the grayscale Alpha channel.

I would like that too.

Maybe 2.0 will make it possible.

8 minutes ago, Friksel said:

Will try the workaround as mentioned by @Lisbon now. Thanks @Lisbon.

Youre welcome Friksel.

[Friksel]

@LisbonIt can be done even easier:

Just add a mask layer to the layer and paint inside that mask layer (select the layer and hit the 'mask layer' button)! No need to merge layers. And semi transparancy is working fine too! 😀

On second thought that's perhaps even nicer to use than drawing on the alpha channel! (although being able to draw directly on the alpha channel is still a great intuitive thing to have, especially when coming from photoshop and perhaps for reasons I'm missing now... [edit] ah, I found one: when you want to work directly into the channel and don't want the hastle to create a mask from an existing channel wich already has alpha. So the mask-workaround is not ideal either...) 

 

[Lisbon]

12 minutes ago, Friksel said:

@LisbonIt can be done even easier:

Just add a mask layer to the layer and paint inside that mask layer! No need to merge layers.

On second thought that's perhaps even better than drawing on the alpha channel!

Your right.

I suggested merging the mask to replicate the workflow related to your question as closely as possible.

 

(To preview the mask you can press Alt + Mouse click on the mask thumbnail)

[Friksel]

28 minutes ago, Lisbon said:

I suggested merging the mask to replicate the workflow related to your question as closely as possible.

I know. And it's probably a great workaround. Thank you for your help!