Scanning line art for press

Question

I would like to know what's the standard resolution for line-art if you'll include it in a for-press production?

I intend on this process:

1. scan image (as RGB or Grayscale)
2. convert to grayscale if scanned as RGB
3. adjust histogram curve (with very sharp contrast line or even direct step from 0 to 255) to make lines with sharp contrast changes or convert to BW bitmap with a particular threshold
4. Save as TIFF

The main question

Would 1200dpi be enough or would I have to scan to 1600dpi to not come out jagged? Or even more? What resolution do you recommend for this kind of images?

Lines are thin.

Answer 1

There are a couple of scenarios to consider here, but the one immutable rule I have always gone by is that scanning 1200 dpi is sufficient for anything to be printed. That being said, there are a number of caveats...

If the line art is straight black and white, no tints or colors, then scan the art as a 1200 dpi bitmap, meaning an indexed color palette of only black and white. This will offer the best balance between quality and file size.

If the line art contains tints or colors, things quickly get complicated because more than likely the art has already been halftoned.

In the case of tints only you can scan the art as gray scale, because doing so offers another best balance between quality and file size. Colors, however, require RGB or CMYK scanning. In either case, 1200 dpi resolution will result in a very large file, so I would recommend only scanning at 600 dpi here.

You will have to play with the color balance to get a pure black out of the lines, but be careful that you don't make the contrast too sharp otherwise the pixels will appear in the printed products. It is better here to let there be some blurring to make the art look better than what it really is.

If the art has been halftoned (you are scanning from an already printed book), then a little work in Photoshop will be needed to turn those half tones into solid colors. Otherwise, if you print already-halftoned art, then that will result in moire patterns which never looks good.

Finally, scanning in RGB is fine because RGB has a wider color gamut than CMYK, but the art will ultimately be converted back to RGB, so some color correction might be in order if you need to match colors.

As always in these scenarios, consider having the art redrawn for best quality. It can cost some money, but the quality will be as tip-top as the art you are scanning.

Answer 2

That's pretty much it, but (3) should be:

• convert to bitmap, adjusting threshold as required.

You don't want grey pixels in the final art, as they'd be halftoned in the print output. Also reduces file size to around an 8 of the original (8 bits per pixel => 1 bit per pixel)