Blend modes work great between layers but can I blend to the canvas?

For example, take this image:

enter image description here

It has an orange square on the left and transparent canvas on the right. I then placed a black-to-white gradient in the middle and set it to the multiply blend mode. On the left (over the orange) we can see the gradient essentially fading from fully opaque black to fully transparent, but on the right (over the canvas) we see no change in opacity or blending, it's still the plain black-to-white gradient.

Is there a way to make the right side blend with the canvas so that it's fully opaque black at the top and fully transparent at the bottom?

I know that I could use the gradient tool to solve the issue for this simple example, but often I have more complex artwork to deal with and having the ability to make blacks solid and whites transparent over the canvas would be fantastic! I think of this as blending to the canvas but perhaps there's another name or tool for this?

Fireworks had a filter called convert to alpha which would get the result I'm after. It would convert your later to gresycale, then anything black would become 100% opaque, anything white became 0% opaque, and all shades of grey would fall somewehere inbetween. I'm looking for an eiquivelant feature in Photoshop!

  • I don't know how to answer this without knowing one of these more complex scenarios where a black to transparent gradient wouldn't work.
    – Ryan
    Commented Nov 8, 2016 at 22:23
  • @Ryan The most recent example I've struck is that a complex shape had an outer glow on to white but now needs to be a drop-shadow onto transparent (so we can dynamically change the colour under the glow). I'm working with legacy artwork so have no source files, if I "blend with the canvas" as described above it would save recreating the shapes from scratch.
    – Andrew
    Commented Nov 8, 2016 at 23:19
  • @Ryan Here's a specific example: This shape is a JPG designed to be on a white background of a website. However the website is having a background colour change so I need to convert this image to a PNG and make the glow fade to transparent instead of fading to white. I could re-draw the artwork and apply a new shadow but it'll be a lot of work as there are a lot of instances.
    – Andrew
    Commented Nov 8, 2016 at 23:25
  • See what I closed it as a duplicate of, I believe the answer with the most votes (not marked the answer) is what you're after. You can also see these two questions which use the same technique for other purposes: graphicdesign.stackexchange.com/questions/12658/… ---- graphicdesign.stackexchange.com/questions/13073/…
    – Ryan
    Commented Nov 9, 2016 at 0:35