How to properly merge a low-quality color image with a high-quality B/W image?

[ATP]

To be sure, I won't include the actual copyrighted material, but I've included examples below to clarify my question. I have a high-resolution map of an area in black and white, and then a color version in lower resolution. I want to merge the two images, to get a more detailed map combined with color information.

Figure 1 and 2 are the two sample images, and figure 3 is when merging them with the color blend mode. It does not give a proper result, with missing and washed out colors. Examples would be the orange roads completely disappearing and lines in the Wellington Barracks area disappearing, in addition to a generally washed-out image. No other blend modes give a good result either, but I might be missing something important.

Figure 1:

Figure 2:

Figure 3 (merged BW + color):

[PaulEC]

It's a bit difficult, without the actual images to play with! But you could try this:

Put the black and white image at the top, with the colour image below. Make sure they align exactly. (Check by temporarily reducing the opacity of the top image.)

Duplicate the lower (colour) layer.

Set the top two layers to Multiply.

Adjust the opacity of the middle layer (colour) if you want to lighten the colour. To darken the text etc you can duplicate the top (b&w) layer.

[ATP]

Thank you for the help.

Multiply results in an image which is too dark, and white text becomes black. No other blend mode gives the right result either with your proposed layer layout.

Without knowing how blend modes work in a technical way, it just seems like something that should be possible. It however might not be the case?

[Ron P.]

10 hours ago, ATP said:

Without knowing how blend modes work in a technical way, it just seems like something that should be possible.

Ok, here you go, some video tutorials explaining how Blend Modes Work in Affinity Photo

YouTube Blend Modes

Also I've played around with your samples. Not really knowing what the result is to look like, I think just working with maybe a Curves Adjustment to increase contrast? It also makes a difference when using Blend Modes, which one is being blended into the other. If you tried with the B&W image on top, then flip them, put the color on top and experiment with the blend modes.

You might also have a look at the Blend Ranges which helps tweak them. It's a very powerful tool.

[ATP]

13 hours ago, PaulEC said:

It's a bit difficult, without the actual images to play with!

1 hour ago, Ron P. said:

...Not really knowing what the result is to look like...

Sorry I forgot to address this. It should look like Figure 2, but with more detail merged from Figure 1. In my mind it's just overlaying low resolution color information on top of a black and white image.

[David in Яuislip]

Resized the colour map to match the bw, nearest neighbour
Colour on top, blend mode darker colour. Experiment with clarity live adjustment layer, increase contrast to taste

[ATP]

46 minutes ago, David in Яuislip said:

Resized the colour map to match the bw, nearest neighbour
Colour on top, blend mode darker colour. Experiment with clarity live adjustment layer, increase contrast to taste

Thank you! That seems to have done it, but I see my example has a big flaw. The graphic I'm trying to merge has text, which on the BW image is black, and on the color image is white. Do you know of an easy way to allow the text to become white, or would manual touch ups be the way? I guess the blend mode does something with complete white that just allows the layer below through.

Added example. The text on the merge picture should be white be becomes black like the BW layer:

 

[David in Яuislip]

I don't understand what you're trying to achieve here, does this screenshot help?

[ATP]

Thanks to everyone for the help, I've gotten very close to what I had in mind. The best solution ended up being the blend mode 'Darker Color' combined with some masking. I couldn't get blend ranges to give a clean enough result.