Replace color on century-old halftone illustration

[GregL65]

I have an illustration from a century-old children's book. It's in color and it's a halftone, so the colors are all made from tiny dots. I want to remove the background colors (replace them with pure white) without making any changes to the animal character. 

The animal character is mostly, but not entirely, outlined in black. When I try flash fill with a low tolerance, it doesn't replace all the dots. If I go higher on the tolerance, then long before it replaces most of the dots it starts replacing color within the animal character.

With the color replacement brush, it doesn't replace it with pure white; instead I get shades of gray dots instead of colored dots.

I considered filling out the black outline of the character, but in places that would spoil the artistic effect.

Any suggestions? I'm leaning toward the brush as that would allow me to leave the character's black border as is. But how do I get it give me plain white instead of gray dots? The black outline is thick enough that my idea is that replacement-brushing it that way would be easier than painstakingly painting pure white around the character.

Any suggestions?

BTW I'm new at this, not just to Affinity Photo but to work like this in general.

Here's the crop from the illustration I'm working with:

Spot_-_Chatterer_from_Twins_p149,_Color_1200,_raw,_rotate,_spot_crop,_BC-HC.TIF

I want to keep the squirrel and the branch he's on, and remove the background sky color. 

Edited June 9, 2020 by GregL65
Adding picture

[firstdefence]

Hi a screenshot or the image would help 🙂

Sometimes there is no fast way to get things done and it sounds like this is one of those times. The colour replacement brush is probably not going to work as you think.
It might be better using a simple brush set to white and brushing over the areas you want white. You could do this on a new pixel layer so you don’t mark the original image but without seeing the art it’s difficult to say.

[GregL65]

Thanks, I've added the picture. 

Is there something I can do with layers to temporarily block off the openings in the black border around the character? So that I could Flash Fill with a high tolerance without changing anything within that border?

[smadell]

I think you should stop trying to select what you want to get rid of (the background halftone dots) and concentrate on what you want to keep. Here's what I was able to do.

(1) Starting with the original image, (2) make a duplicate of that layer (Command-J) and apply a Threshold adjustment. Merge the threshold into the duplicated layer. Now you have a black and white version of your image sitting at the top of the layer stack. (3) Use the paint brush to paint with Black in order to fill in the Outlines of the animal and tree. Use the Flood Fill and/or the Paint Brush to fill in the now-complete outlines with black. You should now have a silhouette of your original image. (4) Invert the layer, and (5) Rasterize the layer to a Mask and drag the mask into the original image to get rid of the background. Put a White Fill layer at the bottom of the Layers stack to provide the new, white background.

[GregL65]

Wow smadell, that is beautiful! This is the first I've ever done anything with layers or masks, thanks so much for the walkthrough.

I decided to keep the part of the branch to the left with the pine cones and tufts of pine needles, so I masked that too; laborious but worth it.

Any thoughts on books or websites that can help me learn more about doing work like this? So many of them seem oriented toward photographers.

[smadell]

Not a clue! Seriously, though, the task at hand here is not that much different from any masking endeavor. If you can learn how to replace a sky (and you’ll find at least 10 gazillion YouTube videos about that) then you can use those skills to work on images like this. Have lots of fun - it’s not just a job, it’s an adventure!

[firstdefence]

There is a section this forum with links to official tutorials, and forum member created tutorials: https://forum.affinity.serif.com/index.php?/forum/9-tutorials-serif-and-customer-created-tutorials/