Convert grayscale image to transparency

[Jonathan D]

I have got a number of picture border files in JPG format I need to convert to transparency in PNG format.

I need pure black to become fully opaque, pure white to become 100% transparent and various shades of grey to become various amounts of transparency.

Some of the files are just pure black and pure white. These are easy to convert: Flood select tool on the white, press delete and instant 100% transparency, then export. It's the various shades of grey I am struggling with. Any help gratefully received.

Jonathan

[Greyfox]

14 hours ago, Jonathan D said:

I need pure black to become fully opaque, pure white to become 100% transparent and various shades of grey to become various amounts of transparency.

Perhaps see if this post helps

 

[walt.farrell]

On 11/3/2019 at 6:05 AM, Jonathan D said:

I need pure black to become fully opaque, pure white to become 100% transparent and various shades of grey to become various amounts of transparency.

If you're using Affinity Photo, you might try the following:

1. Have your image at the bottom of the layer stack, and make sure it's a (Pixel) layer (rasterize it if it isn't).
2. Place a pure black Fill layer below your image.
3. Click on the image in the Layers panel, and invert it (Ctrl/Cmd+I (Windows/Mac)).
4. Right-click on the image in the Layers panel and Rasterize to Mask.
5. Optional: Then drag it to the mask position of the fill layer, or right-click and Mask to Below.

 

[v_kyr]

See ...

• Greyscale to Transparency : how to ?

• Converting grayscale shades into alpha channel

For bulk processing (many images) a tool like ImageMagick might be handy here, assuming an image is a greyscale PNG file then ...

Quote

convert greyscale.png -alpha off -alpha copy -type truecolormatte PNG32:greyscale_alpha.png

... see for ImageMagick and the control of image transparency this here.

[thriva]

Walt.farrell, you're a star. I have been looking all over for the answer to this question.

Many thanks!

[walt.farrell]

Glad to have helped, @thriva, and welcome to the forums.