Screen Tone LPI in Clip Studio Paint: Finding the Effective Line Count After Reduction

What the effective line count is

Line count (lines per inch, or LPI) is the number of screen-tone dot rows packed into one inch, and dot spacing works out to 25.4 ÷ LPI in millimeters. At 60 LPI that's roughly 0.42mm — 10px on a 600dpi source page. Shrink the page for print and that spacing shrinks by the same ratio. What matters to the reader is the line count measured on the printed sheet after that shrink — the effective line count — not the LPI set on the source page.

Reducing a page doesn't remove any source pixels, so resolution isn't the problem. What actually gets smaller is the dot itself on paper, and that's where ink bleed and the print shop's own reduction processing start to bite.

Calculating effective line count from a reduction ratio

Reduction ratio is print width ÷ source width, and effective line count is LPI ÷ reduction ratio. For common doujinshi size pairs, here's what a 60 LPI tone turns into:

• Print a B4 (257mm) source at B5 (182mm) and the reduction ratio is 0.708 — 60 LPI becomes roughly 84.7 LPI.
• Print an A4 (210mm) source at A5 (148mm) and the reduction ratio is 0.705 — 60 LPI becomes roughly 85.1 LPI.
• Print a B5 (182mm) source at A5 (148mm) and the reduction ratio is 0.813 — 60 LPI becomes roughly 73.8 LPI, a smaller jump.
• For that same B4-to-B5 reduction, an 85 LPI tone on the source becomes roughly 120 LPI — raise the source line count first and the increase scales up right along with it.

What happens past 100 LPI

Once the effective line count passes roughly 100 LPI, moiré and clogging risk rise sharply. At 100 LPI the dot spacing is just 0.254mm — only 6px on a 600dpi source — and at that fineness two problems tend to appear together.

• Each dot is small enough that ink bleed (dot gain) lets neighboring dots merge in the shadows, collapsing gradation toward solid black.
• Since the print shop does the reduction, the source page's dot grid can interfere with the output grid, producing moiré that was never in the source file.

That margin of safety is why 55-70 LPI is the common range for doujinshi black-and-white interior pages. Full-size printing can handle up to around 85 LPI just fine, but once reduction is involved, judge by the effective line count instead.

Working backward from print size to source line count

If your print size is already decided, you can work backward to the line count you should set on the source page.

1. Decide the effective line count you want after printing. For black-and-white interior pages, around 60 LPI is a manageable target.
2. Work out the reduction ratio (print width ÷ source width). Printing a B4 source at B5 gives 182 ÷ 257 = 0.708.
3. Calculate source line count = target effective line count × reduction ratio. 60 × 0.708 = 42.5, so set the source to 42-43 LPI.
4. Check that the resulting dot spacing isn't too fine for your source resolution. At 600dpi, 42.5 LPI gives a spacing of roughly 14px — plenty of room to render the dot shape cleanly.

What you type into Clip Studio Paint's tone settings — the Layer Property palette, or the dialog for creating a tone layer — is this source-side line count, the Frequency value. Type your print-size line count in there instead, and the tone comes out finer than intended once reduced.

Checking how it looks on screen

Once you've settled on the numbers, check how they actually look at true size. Enter the paper size, print resolution, line count, density, and angle, and the preview draws dots at true paper size, with a reduced-print conversion field that gives the effective line count directly from a source size and a print size. Complete the actual-size calibration first, and 100mm on your monitor matches 100mm in the real world, so you can judge dot coarseness from normal reading distance. Overlay moiré is checkable on the same screen, by sweeping the angle offset between two overlaid tones.