Huh, mine corrects itself. Not sure what yours is up to

If you want to blend two images equally (a 50/50 mix), then each image should contribute 50% opacity.

Image 1 opacity: 50%

Image 2 opacity: 50%

That way, when composited, each pixel in the result is exactly halfway between the corresponding pixels of the two source images.

One subtlety: If you simply stack one image over the other and lower the top layer’s opacity to 50%, you’ll effectively get 50% of the top image + 50% of the bottom image. But if you lower both to 50% and put them on separate layers without special blending, depending on the software, you might not actually get a true 50/50 blend — it could look faded.

The cleanest way (in Photoshop, GIMP, etc.) is to keep one image at 100%, put the other above it at 50% opacity. That produces a proper 50/50 blend.

Do you want me to walk through the math of why lowering both to 50% doesn’t give you a true 50/50?