problem making a picture background transparent

[Csaba]

I want to make a picture's background transparent in order to replace it with different colors. My goal is to easily change only the background while keeping the main image intact.
From this  to (red BG)  or (green BG) ...
 

Here is my workflow:

1. Opening the image.
2. Adding a new layer.
3. Setting the layer's opacity to 255 and the blend mode to "Normal".
4. Selecting the new layer.
5. Using the Gradient Tool (in radial mode).

About the colors: For both the foreground and background, I set the opacity to Alpha 0, as described here. 

 

  and 
for the mode I use Transparency mode 

And drawing the gradient, nothing happens. 

I can't see the desired background transparency squares in the image.
Switching back to color mode, I expect to see the RGB part of the gradient (the blue I selected for the foreground), but nothing appears.

The interesting thing is that yesterday I was able to perform this process successfully. Now I'm disappointed because I can't figure out what I'm missing.

Even after finishing the gradient and flattening the layers, still nothing. I exported the file in PNG 32-bit, so I'm confident the format is correct.

Please give me an idea of what I might be missing here. Thanks.

Edited September 12 by Csaba

[frio]

I think you're mixing up two modes of operation here.

 

If you draw a transparency mode gradient, the colors must be opaque (the opacity is the "strength of the transparency gradient" as it were) and it must be drawn on the layer you want to make transparent, not a separate one.

 

Layers + radial gradient with a transparent middle. Note that you wouldn't even strictly need a layer to draw a semi-transparent gradient on something as long as the blend mode of the tool isn't set to overwrite, but it will make doing adjustments easier:

[Ego Eram Reputo]

Quote

I want to make a picture's background transparent in order to replace it with different colors. My goal is to easily change only the background while keeping the main image intact.

 

You'll need two layers. Arrange them like this....

 

Put your foreground objects on their own transparent layer.

Drag the foreground layer higher than the Background layer.

Put whatever gradient or color on the Background layer.

 

 

Change or replace the contents of the Background layer as many times as you wish.