I want to replace the black color in this image with transparency. This would also mean that the gradient in the center of the image would not fade to black but fade to transparency. How is this possible?
The general approach with a solid-color b/g:
For this to work your image must be RGB. If it isn't already make an RGB copy. If there are different shades of black in the background, you have to do this for each group of pixels that have a different RGB definition. In other words, it's easy with a solid-color background and increasingly time intensive depending on the number of RGB combos in the graphic's background.