Saving a bitmap with alpha channel

[Josh]

I'm trying to convert this PNG image into a bitmap and retain the alpha channel, and nothing is working. Does anyone know how to do this?:

http://a2.mzstatic.com/us/r30/Purple6/v4/45/99/be/4599beb5-9f5b-820b-c0b4-7936727f6949/icon256.png

[martyj]

What are you using to convert it?

 

I only have GIMP at work.

http://martyj.phpdev.gurutech.ws/images/icon256.bmp

[macklebee]

I only have GIMP at work.

http://martyj.phpdev.gurutech.ws/images/icon256.bmp

What options did you use to save? Just wondering because the alpha is there but it removed the color from the non-alpha parts when brought into the Editor as shown in the picture on the left.

When I saved Josh's png using Gimp as a 32-bit A8 R8 G8 B8 bitmap, it looks like the one on the right when brought into the Editor.

icon256_32bit.bmp

[Josh]

The bitmap you posted above has a black background shown in Windows Explorer, and when the Windows API loads it.

 

I am doing OS graphics stuff, not Leadwerks textures.

[tjheldna]

Try this. It's saved as a 32bit with a calculated alpha channel.

 

icon256.bmp

[Josh]

Dude, just look at the image icon on your desktop. If it's not transparent, it;'s not working.

[gamecreator]

They are all transparent, even if the desktop icons don't represent them correctly. Open them in a free program like XnView which lets you change the background, set it to something obvious like orange and you'll see. macklebee's version seems to preserve the shadow at the bottom correctly too.

 

You can change the background color in XnView by going to Tools, Options, View (on the left), Background Color. You may have to restart the application to display the images correctly.

[knocks]

A bmp would need to be converted to an ico file to show a transparent preview on the desktop.

[gamecreator]

Josh's original PNG also shows transparency correctly as an icon but apparently BMPs don't, at least on some OSes.

 

The BMPs also load differently in Photoshop - they come with a separate Alpha channel layer. The PNG doesn't and yet it has transparency as well.

[martyj]

My Bitmap does have transparency. I loaded it in a web browser changing the background color to whatever I wanted.

 

http://martyj.phpdev.gurutech.ws/images/icon256.html

 

Windows might not show the color right in explorer.exe. But the color is right.

 

Here is the options for exporting.

 

What are you trying to do in win32? Set an icon for a button?

[Josh]

Hmmmm, it looks like Windows doesn't support bitmaps with alpha channels?

[Athos]

-Deleted-

[Josh]

Okay, thank you all for your suggestions.

 

It turns out GDI+ has a nicer image drawing function and it supports PNG files.

[Bolt]

Just some extra info if anybody is interested.

 

PNG files support transparency, but they don't utilize it as an alpha channel, like you might find in 32-bit TGA or BMP files. If you load this PNG file into Photoshop, you will see transparency, but no alpha channel. Which may seem a bit confusing.

 

In Photoshop, you can convert transparency to an alpha channel, by Ctrl+clicking on the layer icon, then open the Channels window, and click on the "Save selection as channel" button, to create a new alpha channel. This can then be saved as a 32-bit TGA or BMP file.

[gamecreator]

Good info Bolt. Thanks.