1 Bit Images Recommended Resolution.

Here are the settings I use:

Scan in Line Art or Black-and-White mode. I believe it is actually 2 bit--on and off bits. (Bitmap mode in Photoshop)

Scan at 1200-1800 ppi (I believe 1500 is the maximum resolution the human eye can discern.)

Save as LZW-compressed TIFF.

Many graphic programs can treat the white bit as transparent.

What is it about binary images that requires a higher resolution?

For print output gray pixels have to be converted into a screen pattern. For offset printing the pattern usually is a halftone screen where an illusion of gray is created by changing the size of the halftone dots. The halftone screen has it's own resolution (lpi), so for 8-bit images there is a diminishing return on higher image resolutions because the halftone screen obscures the image details.

With 1-bit images there would be no halftone interference between the black and white pixels, so there has to be a higher resolution if you want to fully resolve the high contrast details.

So these gray values would get screened at output

The halftone screen limits the possible edge detail:

While with a 1-bit black and white version there is no halftone screen interference and the edge pixels are visible at lower resolutions:

BecJM  wrote ... What is it about binary images that requires a higher resolution?

That depends on their actual contents. If we talk about high contrast details that are a bit skewed you will notice that downsampling images like that usually is no good idea.

Regards,
Uwe

If you want the exact specifications for anything in a print project, call your printer. They know better than anyone what is needed.

You should definitely not just use existing preflight profiles. Think of them as examples to look at, before setting up profiles that match YOUR needs and workflow(s).

Hi BecJM ,

you mentioned just default settings of InDesign preflight. Change them as you like or your project requires.

Usually 1 Bit images require a higher resolution than grayscale or color ones, because there can be no antialising of high contrast details.

600 ppi or even 1200 ppi effective resolution would be ok.

In the rare case that all image details, thin lines, edges etc. are aligned perfectly horizontally and vertically lower res images are ok as well.

Regards,
Uwe