Transparency when drawing two bitmap images


I am currently trying to display two bitmaps on the screen at the same time. My issue is one of the bitmaps is covering the other one. I want to create it so that you can see the image of the bubbles through the tank window.

Sorry I forgot to mention I have bmp images. I am not trying to use png ones. This is just for a reference.
Image 1 Tank

Image 2 Bubbles

Any help would be appreciated

You are not, I am almost certain, displaying two pngs simultaneously. Why would you then post them (incorrectly) in some other format?

You need to set the background color of the foreground image to transparent.

How to do that is NOT specific to using the bitmap file's contents on the Arduino.

Your display or library does not know how to deal with PNG files most likely

If you use 1 bit black and white images then it does not deal with transparency

You need another buffer where you will do bitwise operations to composite your "transparency" by doing operations at bit/pixel level to decide what's visible or not and then display that calculated buffer

For example initialise your buffer by copying the tank window, overlay one by one the pixels of the bubbles bitmap (possibly with translation if this has to be animated) but only turn on a black pixel in the target buffer if the bubble bitmap pixel is black - don't erase existing black pixels with the white ones from the bubble bitmap