How to get original watermark having any images with it?

Question

Watermark

Found the formula
Rmix = R1*(1-alpha) + R2 * alpha
Gmix = G1*(1-alpha) + G2 * alpha
Bmix = B1*(1-alpha) + B2 * alpha
Where Rmix is ​​the color (red channel) obtained as a result. R1 is the color of the original out. and R2 is the color of the watermark. Knowing the value of transparency with which the watermark was applied (alpha), you can calculate all its colors. As far as I understand.
I tried watermarking on black and white backgrounds. And using this formula to calculate the desired color.
I started solving this problem jokingly. And I have already spent several hours to no avail ... Now it does not go out of my head