32 Bit PNG's won't save as png?

Question

Just for some background knowledge. I am absolutely terrible with graphics, but I attempt anyway. I am trying to create a dead simple graphic for my Android APplication while trying to follow the guidlines set by Google. (http://developer.android.com/guide/practices/ui_guidelines/icon_design_action_bar.html)

They state: Action Bar icons should be 32-bit PNGs with an alpha channel for transparency

I tried to set that type of project up in photoshop, but now it won't let me save as a PNG.

Just as an addition to this, they state that ActionBar icons should be 32x32dp. How can I make an icon using those guidelines?

Answer 1

32bit refers to 8 bits per channel for red, green, blue and alpha. In Photoshop, that's called 8 bit mode. 32 bit mode in Photoshop refers to 32 bits per channel, meaning 128 bits in total (32each for red, green, blue and alpha).

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32×32dp (display points) works out to be 32×32 pixels for mdpi, 48×48 for hdpi, and 64×64 pixels for xhdpi. Those are the pixel sizes you'll need for a the icon you're after when building a modern Android app.

So, just to clarify, you're after 3 final icon sizes.

• 32×32 pixels at 8 bit per channel for medium DPI.
• 48×48 pixels at 8 bit per channel for high DPI.
• 64×64 pixels at 8 bit per channel for extra high DPI.

Once you've created your Photoshop document and icon, you can use Save For Web to save the image.

Answer 2

This isn't my speciality but if you look at the example icon they give, it is 256x256px, 8bit. Perhaps the miscummunicatio here is 8 bit per channel = 32bit?

Either way, they also supply templates for Photoshop here: http://developer.android.com/guide/practices/ui_guidelines/icon_design.html#templatespack

Hope that helps