Paint.NET question

[d000hg]

Just in case anyone here knows...

I have a greyscale BMP image, basically black text on white background white but with some anti-aliasing introducing more shades of grey. In Paint.NET I want to save this as a PNG, with transparency based on the whiteness... e.g black is opaque, white is fully transparent, so I can place this image on top of other things and the antialiased text blends properly.

I'm sure it can be done but I can't figure out the right way.

[doodab]

What you want is an alpha channel.

Alpha compositing - Wikipedia, the free encyclopedia

[d000hg]

I know. I want to know how to do it specifically in Paint.net, to use the black/white channel for alpha. Or alternatively how to do some clever fill using transparent colour that will respect the grey-scale .

[London75]

I haven't got Paint.NET at the mo but I think you need to do black text on a transparent background rather than white background for the effect you require. The white is blending so you're getting a black to white palette and what you want is a black to transparent palette.

Hope that makes sense.

[doodab]

Ah right.

I think if you:

change the background opacity to 0 in layer properties

create a layer with the blending mode set to "multiply" and opacity set to 255

Place the text on that using the text tool

save as png, in the dialog make sure you select 32 bit

That should do the trick.

[d000hg]

Unfortunately it's not text I can retype... I have a BMP. I basically want to add an alpha layer manually, using the source colour data to control the per-pixel alpha.

It seems like a fairly common thing - take an image and try to make the background colour transparent.

[Spacecadet]

Unfortunately it's not text I can retype... I have a BMP. I basically want to add an alpha layer manually, using the source colour data to control the per-pixel alpha.

It seems like a fairly common thing - take an image and try to make the background colour transparent.

Do you want to add the text to the other image in paint.net or is to be overlayed else where?

step by step

1. add layer with text
2. add image layer
3. ensure that text layer is above image layer in the layers toolbox
4. double click text layer and change blending mode to multiply

[Spacecadet]

There is also a plugin here which will give you the effect you want, i.e. a .png with a graded transparency for the anti aliasing:

Make Transparent plugin - Paint.NET Forum

download the .dll and copy to the Effects folder:
C:\Program Files\Paint.NET\Effects