Convert alpha channel (render pass) to spot channel

[Dmi3ryd]

Hello.

Once again I want to thank the Affinity Photo development team for amazing package for working with graphics.

I have a very simple question.

After rendering, I have an alpha channel as a separate file (render pass file).

Could you please tell me how to quickly convert an image (layer) into a channel for selection?

Most importantly, when converting an alpha image with to spot channel, there should be no loss in white gradation.

Or use this alpha image as a brightness mask, where white hides the image, black leaves.

Thanks.

[stokerg]

Hi Dmi3ryd,

Can't say i've much 3D work like this (i've just not had the need).  But i suspect if you see this tutorial it will help: https://affinity.serif.com/tutorials/photo/desktop/video/365275093/  

[James Ritson]

On 7/6/2020 at 11:43 AM, Dmi3ryd said:

Hello.

Once again I want to thank the Affinity Photo development team for amazing package for working with graphics.

I have a very simple question.

After rendering, I have an alpha channel as a separate file (render pass file).

Could you please tell me how to quickly convert an image (layer) into a channel for selection?

Most importantly, when converting an alpha image with to spot channel, there should be no loss in white gradation.

Or use this alpha image as a brightness mask, where white hides the image, black leaves.

Thanks.

Hi @Dmi3ryd, the video Gareth posted would help with making selections from Material/Object ID render passes (or Cryptomatte in its bitmap form). However, it sounds like you just want to convert a pixel/image layer to a mask, is that correct? If so, copy/paste or place your alpha image into your document, then go to Layer>Rasterise to Mask. Alternatively, you can right click the layer thumbnail and Rasterise to Mask will be on that menu too.

Once the layer is a mask, you can mask other layers with it (drag-drop over the layer thumbnail, not the label text), and you can CMD-click (Mac) / Ctrl-click (Windows) the mask layer to create a selection from it. Finally, with the mask layer selected, you can also go to the bottom of the channels panel and right click [Layer Name] Alpha then choose Create Spare Channel. This will create a channel from the mask which you can load into other masks or into your active selection.

PS if you want to invert a mask, just select it and use Layer>Invert, or CMD+I (Mac) / Ctrl+I (Windows).

One final note: if you need to multiply or divide alpha by the colour values, you need to flatten the mask into its parent pixel layer first. With a mask clipped to a layer, right click the parent layer and choose Rasterise. Now, on the Filters>Colours menu, you have Multiply by Alpha and Divide by Alpha. You can also do this non-destructively with a Live Procedural Texture filter, but that's for another day 😉

Hope that helps!

[Dmi3ryd]

Quote

However, it sounds like you just want to convert a pixel/image layer to a mask, is that correct? If so, copy/paste or place your alpha image into your document, then go to Layer>Rasterise to Mask. Alternatively, you can right click the layer thumbnail and Rasterise to Mask will be on that menu too.

Thank you very much! This is really what I need.

It's very sad that, a simple layer cannot be used as a mask.
For example, I have a separate source file with rgb alpha channel and I add it to the project as a smart object.
In order to use it as a mask, I need to rasterize it. But what if the mask is always updated?
Here it would be great to add the ability to use an ordinary layer as a mask with the ability to automatically update the content.
It would be very convenient.

Thanks again for you help!

[lepr]

3 hours ago, Dmi3ryd said:

It's very sad that, a simple layer cannot be used as a mask.
For example, I have a separate source file with rgb alpha channel and I add it to the project as a smart object.
In order to use it as a mask, I need to rasterize it. But what if the mask is always updated?
Here it would be great to add the ability to use an ordinary layer as a mask with the ability to automatically update the content.
It would be very convenient.

Any object can be non-destructively used as a mask.

To use the object's opacity as a mask, just mask-nest it in the object to be masked.

Using an object's luminosity as a mask is only a little more complicated. The trick is to non-destructively map the object's luminosity to alpha and mask-nest it in the object to be masked. Luminosity to alpha can be achieved with the Source Layer Ranges curve of the Blend Options of any object, or with a Channel Mixer Adjustment.

(This is how I overcome the current inability to use all pixel-editing tools on objects of type Mask - use a Pixel object with luminosity mapped to alpha.)

Also, to get a luminosity-based selection from any object, opt+cmd click its thumbnail.

Edited July 25, 2020 by anon2

[Alfred]

1 hour ago, anon2 said:

Also, to get a luminosity-based selection from any object, opt+cmd click its thumbnail.

On Windows, Alt+Ctrl-click.

[lepr]

Just now, Alfred said:

On Windows, Alt+Ctrl-click.

Windows is against my religion 

 

[Dmi3ryd]

Thank you guys so much! This is very useful information!
Sincerely.