How to Emboss GeoTIFFs in QGIS

[PecuTheGreat]

Or maybe another way to phrase it is how to add the % height values of one .TIFF file over another?. Or how to merge two .TIFF files but only a percentage of the value of one and the full value of another.

So essentially, a friend embossed 1/3rd the transparency of the height map of glacial Europe on a map of modern geography, to produce this map below. How can I do the same but with a .TIFF file on QGIS?.

Europe_Iso.png

[waldronate]

The hardest part of most searches is getting the correct terms.
https://www.google.com/search?q=how+...t+maps+in+qgis might get you started (I haven't used qgis much or at all in about ten years).