I have spent more time than I can to admit trying to come up with a solution that doesn't require bringing the layers into Photoshop or the GIMP (which would take an insane amount of RAM/swap space to work on this).
Here's the setup: Using QGIS 2.8.1 on Ubuntu. 2 layers imported, both have srs and align properly.
Layer 1: Low resolution color imagery for the entire planet Layer 2: Higher resolution B&W imagery for an entire planet
I'm using the color information from Layer 1 and overlaying it on the higher resolution B&W imagery of layer 2. To do this, I use the following:
Layer one: Properties: Color rendering: Blending mode: Hard Light Layer two: Properties: Band rendering: Contrast Enhancement: No enhancement Layer two: Properties: Color rendering: Contrast: -15
After setting these values, the resultant two datasets look very good over one another.
Now, my issues as I see them:
- I need to merge the two layers into one
- I need to export the resultant merged layer into a geotiff
I can figure out #2 okay using layer: Save As: Output mode: Rendered Image, etc
But, what I cannot figure out is #1.