Add an image button with transparent background

Question

I want to add image buttons on my main app screen that have a transparent background. I have created the images in GIMP and saved them with transparent backgrounds in png format but when I add them to my android app in Eclipse they appear with a white background. How do I remove this in my code?

Answer 1

Try using null for the background for your image button in the xml layout.

android:background="@null"

Answer 2

A transparent background generally works when used in photoshop, if it is not, you have to set the alpha bits of the pixels around the border of your image

use alpha-masking( subset of alpha blending, google them to know more).

A little theory: depending on the alpha bits for each pixel in your Bitmap (the translucency bits), the extent of blending of that pixel with over-written pixel is determined. Considering extremes, if alpha is 255, overwriting pixel is used instead of the over-written one (fully opaque, in regular terms); if alpha is 0, overwriting pixel is just ignored (transparent). For other alphas in between: there is blending.

In your case you would have to make the alpha of the border zero, to achieve complete blend. Outlining all the steps in geral:.

1. The drawable to be used can't be a JPEG( JPEG doesn't store alpha values per pixel). Go for PNGs

   2.You will need to create and keep your bitmap drawable in that way beforehand(use google for alpha blending PNGs) such that the borders have zero alpha value ( use softwares like Paint.NET for ex).

2. If images are being created dynamically, you would need to use a blending equation ( for details read materials by Porter and Duff).

   For ex, this is PNG image with transparent pixels having alpha 0 other than the alphabet itself
   .

Above is the alpha blended PNG on colored background of an Activity. I hope this is what you really want to achieve.