npr op• 数据种类:image2d → image2d
• 调用: import fullseye as fs; fs.ledger.halftone_screen(image, lpi=60.0, angle_deg=45.0, pixel_um=25.4, sharpness=8.0)(要直接调用实现,import printpath; printpath.halftone_screen(image, lpi=60.0, angle_deg=45.0, pixel_um=25.4, sharpness=8.0);从台账取用则 opsprintpath.get("halftone_screen"))
经典的旋转半色调网屏 —— 网点面积承载灰阶。
> 以下的详细说明为原文 —— 摘要与标题已翻译。
Thresholds the image against a rotated periodic spot function (the product of
two shifted cosines, the classical round-dot screen). *lpi* is lines per inch
and *pixel_um* the pixel pitch, so the screen frequency in pixels follows the
printing convention rather than a bare "period in pixels".
★Why this earns its place: two screens at different angles beat against
one another, and the period and direction of that moiré are a closed form
(:func:halftone_moire_period) that can be predicted *before* anything is
drawn and then measured out of the image. That is why newspaper printing puts
the plates at 15°/45°/75° — the beat is pushed to a frequency the eye does not
resolve — and this op lets that be shown as numbers, not folklore.
Parameters
----------
image : 2-D array in [0, 1]
Tone; 0 prints solid, 1 prints blank (the ink is `1 - image`).
lpi : float
Screen ruling, lines per inch. Newspapers use 65-85, magazines 133-175.
angle_deg : float
Screen angle. The classical set is K 45°, M 75°, C 15°, Y 0°.
pixel_um : float
Pixel pitch in micrometres (25.4 um = 1000 dpi).
sharpness : float
Edge hardness of the dot; large values give a hard threshold.
Returns an `image2d`: 1 = paper, 0 = ink.
Raises `ValueError`: non-positive lpi, pixel pitch or sharpness; a screen
period below 2 px (it would alias — reported, never silently drawn); a
non-finite or oversized image.
Limits: this is a *screen*, not a printer. Dot gain, ink spread and
registration error are not modelled, so measured ink is the geometric
coverage and will read lighter than a real press.
• 示例数据目录(下载 URL / 许可证) —— 2-D 用 skimage.data(BSD/公有领域)加合成图,3-D 给出真实数据源(Stanford/PDS 等)的下载 URL。
• 算子来历与参考文献 —— 该算子族所依据的研究/方法出处。
• 算法的正典(作者・年份)与用途见上面的族使用指南。
• poc_beats_fringes_and_screens — py -3.11 examples/poc_beats_fringes_and_screens.py
• poc_print_registration — py -3.11 examples/poc_print_registration.py
image2d 作为输入)stipple_points_from_image · stipple_energy · stroke_tone_error · engrave_lines · hatch_field · mosaic_tiles_sites · mosaic_tiles_render · print_layer_defect_map
npr)halftone_moire_period · engrave_lines · hatch_field · mosaic_tiles_sites · mosaic_tiles_render
*Provenance: printpath.py — PRINTPATH 算子登记表。本条目由 tools/opdocs.py md 自动生成(请勿手工编辑)。*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.