Exporting pictures with a mask

It sounds like it’s still not understood, so I’ll try…

The masks in the Adobe parametric raw processors (Lightroom, Lightroom Classic, Camera Raw) are not applied at the file level. They’re applied at the edit level. You create a mask for a specific edit, so the mask is for that edit…part of that edit is transparent, where the mask is. But the image still has an opaque background. There is no mask that creates transparent areas for the image itself.

This is actually very similar to how masks work in Photoshop and other non-raw/non-parametric image editors, where a mask is always attached to a layer. If you have a Photoshop document with an opaque background, it doesn’t matter how many masks you add to the layers above it, you are not going to get a transparent background when you export.

If you are trying to use a mask to cut out a subject and export an image with a transparent background, what you’re looking for is an alpha channel on export — to include a mask that applies to an entire image so that its background is transparent in other applications. 

Unfortunately, there is no support for alpha channels in Lightroom/Lightroom Classic/Camera Raw. Every image exported from that software has an opaque rectangular background.

If you need to export transparency behind the subject of an image:

1. Open it in Photoshop. 

2. Select and remove the background. 

3. In the Layers panel, confirm that the bottom layer is not named “Background” with a lock icon. (If it is, then it’s an opaque background.)

4. Export to a file format that supports alpha channel transparency, such as PNG.

This is a common misunderstanding. A mask is not an edit. It is a way to visualise where certain edits (that you make with the sliders) will be applied and where they won't be applied. On export only those edits will show in the exported image, not the mask itself. That means that if you create a mask but do not apply any edits, your exported image will be the original non-masked image.

As a practical example: suppose you use the AI Select Sky mask. If you turn on the mask overlay, then the sky will be red. That does not mean you have now made the sky red, it means that Lightroom is telling you "what is shown in red is what I consider to be the sky". If you now lower the exposure slider of the mask, then that area will be darkened. The exported image will show the darkened sky, not a dark red sky,

Whatever is applied in the mask is an attribute that becomes part of the exported image. But the mask itself does not export. The attributes of the mask become part of the image but the mask is gone. The mask only exists in the master image.

A "Mask" is only a temporary visual indicator for where you make an editing adjustment (eg. Exposure).

A visible mask (the 'Overlay') does not alter or export with the image. Only the applied develop/edit adjustments (under the mask) get applied to the exported file.

Because a mask can be changed in color (Red > Green > Mono > White, etc) it can cause confusion thinking that an edit adjustment has been made.