How to scan B&W line art

Here's a method I have used to scan my comic line art since around 2005. I can't recall exactly where I learned this technique, but at the time I confirmed that it was standard practice by a couple of other professional comic artists.

It might seem excessive but it gets impressive results and despite what you may think, it produces file sizes smaller than jpegs at a third of the resolution. It also produces the most accurate and crisp line art you can imagine.

1. Scan art work at 1200 DPI greyscale or export your image from elsewhere (IE Procreate etc)
2. Open in photoshop (Crop, resize, transform how you want)
3. Clean up artwork using you preferred method (for smudges, stray dot, inks spills, mistakes etc)
• levels
• threshold, 
• eraser tool 
4. Change the colour mode: Image / Mode / Bitmap
5. A context menu appears with options, chose
1. Output 1200px per inch
2. Method: 50% threshold
6. File / Save as / TIF / LZW compression

Now you have a super hi resolution digital file of you artwork that you can use for printing. The file size is even more reasonable than a jpeg thanks to the LZW compression option. This method also works for colour pieces but requires some extra steps.

Steps for colouring in Photoshop

1. Prepare your b&w artwork as above
2. Make a copy of the file (as not to overwrite your hi-res B&W file
1. File / Save As / jpeg (or whatever works for you)
3. Once saved, revert back to greyscale: Image / Mode / Greyscale
4. Reduce image size: Image / Image Size / Resolution [change to] 300dpi
5. Create a new layer/s for colour
6. Put B&W line art layer to blending mode / multiply
7. Colour artwork as best you see fit
8. When done colouring, turn off all layers except colour
9. Open up Adobe Illustrator (or similar software)
10. Create a new file the final print dimensions of your document
11. Place the colour jpeg file
12. Then place the B&W line art over that (they have the same dimensions, although one has a 300dpi resolution and the other 1200dpi, they will line up exactly)
13. Save as a PDF (or whatever file you need)

Steps for colouring in Procreate

you have two ways to do this, either draw the colour layer in your original line art file (I make my line art files either 600 or 800 DPI) or make a copy of your line art file (IE 'Duplicate') and then reduce the DPI in menu, resize canvas to 300DPI. My preference is to do the colour in my hi-res line art file and shrink it down later (or not depends on files sizes and memory, storage etc).

The instructions are then the same as above from no.9 down. However I'll write it up as is you're using Affinity Publisher for layout

1. Open an Affinity Publisher file the size of your page
2. After you've tweaked your margins and page guides etc place down a picture frame 
3. Place the 300 DPI colour file down
4. create another picture frame the exact same size and place the b&w art down
5. Turn the b&w layer to multiply. Both files should align perfectly without the need to adjust
6. File, Export to PDF (note you can save to jpeg from her but that will compress your hi res line art

This way you have the colour saved at a reasonable DPI (and file size) and the super hi res and crisp line art goes over the top. It might sound crazy but it results I impressive results with manageable file sizes.

I found this True Grit overview of using 1200DPI bitmapped Tifs useful, https://www.truegrittexturesupply.com/blogs/news/1200dpi-or-die 

Note: I've always done this in Photoshop. As far as I'm aware you can't do this in Affinity as of writing this. It might be possible in Clip Studio (based on a cursory google search)  but I have never used the software. I currently do not support Adobe and would like to find a new way to do this outside of their eco system.