How to find the alpha channel transparency value of a pixel in a png image?

Question

I have an image that has alpha channel transparency, something like the image below.

http://yfrog.com/86tagsp

I want to recreate the same background color with rgba values in CSS but I can not find the real color of the background pixels and their alpha channel value. if I use any sort of color picker it will give me the absolute value of the pixel color which is relevant to its background color.

do you know any trick to find out the real alpha channel value of a pixel?

Answer 1

use the absolute colour and adjust the transparency in photoshop until it looks right and then use that percentage as your value.

Answer 2

In Photoshop's Info panel, you can choose 'Opacity' as a readout mode, though it will show up as a percentage and not as a real alpha value.

To enable it, simply open the Info window, choose Panel Options and then set the Second Color Readout mode to Opacity.