There should be many online tools to test images (or screenshot of pdf) and simulate how they look for various colour blindness impairments. With a quick google search I found this:
There may be different conversions from rgb to grayscale but the differences are minimal. If you take a light ...
You can do this:
Find a common part of the image. Make measures, in my case I've picked the height in pixels. The right dimension image part has 50px height, the wrong one has 70px height.
I just divided the right height by the wrong one then multiplied by 100.
This way I found the right percentage I must reduce the wrong image.
Now I can scale it using that ...