Manhwa cropper for long webtoon images

A manhwa cropper solves a delivery problem that appears after a vertical episode has been assembled. Artists may work on one continuous canvas because scroll pacing, transitions, and repeated backgrounds are easier to judge as a whole. Publishing systems, review tools, messaging apps, and client handoff folders often need shorter files. Manually copying rectangles can be slow and introduces practical mistakes: a skipped strip, duplicated pixels, inconsistent dimensions, an incorrect filename order, or a cut through a face, speech balloon, sound effect, or action line. This page turns one approved long image into a numbered set while keeping the proposed result visible before download.

The first control is output height. It is a target, not a promise that every slice will have the same height. If safe-margin search is enabled, the algorithm can move a boundary upward or downward to a row that appears visually empty. The safe margin defines how far it may search around the target. A 2400-pixel target with a 180-pixel margin asks for a useful height near 2400 while permitting a cut between 2220 and 2580 when a better blank band exists. The final slice is normally shorter because it ends at the bottom of the source.

The source file is validated twice. The browser checks the MIME type, byte size, decoded dimensions, and practical canvas limits. After sign-in, the server checks the declared type, size, and leading file signature. The server does not retain the image during this validation route. The browser then decodes, scans, crops, encodes, previews, and packages the slices locally. This is a deterministic utility, not an AI image generator, and it does not spend generation credits.

Ordered naming is part of the functional result. Each filename uses the source basename followed by a three-digit sequence, such as episode-07-001.jpg, episode-07-002.jpg, and episode-07-003.jpg. The sequence reflects top-to-bottom reading order, not panel numbers. Keep the original basename short and versioned before processing, because operating systems and publishing dashboards may truncate long names. If the same episode is exported again with different settings, place the new set in a separate review folder instead of mixing versions. The cropper does not overwrite local files automatically, but a browser may append duplicate-name suffixes during repeated downloads. Verify the extracted ZIP rather than relying on a downloads folder that already contains earlier tests.

Choose height from the requirements of the actual destination. Do not copy a platform number from an old checklist without checking the current publishing interface, because upload limits and recompression rules can change. If a client asks for 2000-pixel segments, enter 2000 and choose a margin that is large enough to reach the gutters already present in the episode. A margin of zero creates fixed-height cuts. A modest margin works for regular panel spacing. A large margin gives the algorithm more freedom but can create visibly uneven slice lengths.

The tool accepts an output height from 500 to 8000 pixels and a search margin from 0 to 800 pixels. These product limits keep previews and exports manageable in common desktop browsers; they are not universal manhwa standards. A slice cannot be shorter than roughly 55 percent of the requested height during normal blank search, which prevents a strong empty band very close to the previous boundary from creating a useless sliver. The last slice is exempt because it simply contains the remaining pixels.

PNG is lossless and is appropriate when line clarity, flat colors, transparency, or repeated editing matters. It can create large files for painted episodes. JPG is smaller for photographic or softly rendered pages but does not preserve transparency and introduces compression. The quality slider applies only to JPG. Neither format creates editable panels, lettering layers, or source document structure. The export uses the decoded source width and the planned vertical region; it does not upscale, sharpen, or redraw the comic.

Export the long episode after lettering, color correction, and final layout approval if the slices are intended for publication. Cropping too early creates avoidable version drift: dialogue may move, a panel may grow, or a transition may be inserted after filenames have already been distributed. Keep a layered master in the original drawing application. The cropper works from a raster delivery copy and returns raster slices. It cannot restore layers, vector balloons, fonts, or hidden artwork outside the exported canvas.

Make transition space intentional. When possible, leave a visually quiet horizontal band between story beats. Keep faces, hands, speech balloons, captions, and important sound effects away from likely cut zones. If a background must continue across a boundary, accept that the best automated cut may still pass through it and check the seam manually. Remove accidental transparent padding at the top and bottom unless it is part of scroll pacing. Confirm that the source is upright and that its filename identifies the episode and version.

Very large images can exceed a browser’s image-decoding, memory, or canvas limits even when the file is compressed below 25MB. This page limits decoded width to 4096 pixels, height to 50000 pixels, and total pixels to 40 million. Those are defensive product constraints, not guarantees that every device can process the maximum. Close memory-heavy tabs, use a desktop browser, or export the episode in two source sections if decoding fails. The interface keeps your non-file settings in session storage, but browsers do not safely persist the local file across a login navigation, so select it again after returning.

The current implementation applies a stricter pre-decode safety gate of 40 million pixels and estimates roughly eight bytes of working memory per source pixel for decoded and intermediate data. It rejects an estimated workload above 320MB before creating the image bitmap. The estimate is deliberately conservative but cannot account for every browser’s internal copies, color conversion, GPU texture allocation, or memory already used by other tabs. A device can still fail below the limit. When that happens, do not repeatedly retry the same maximum-size file; split the master into two source exports at an intentional gutter and process each set separately.

The cropper cannot understand narrative pacing. A technically empty band may be the wrong place to end an upload segment if it separates a setup from its reaction, weakens a reveal, or places an important beat at an awkward loading boundary. It cannot identify platform-specific content warnings, episode covers, paid-preview cutoffs, ad markers, creator notes, or music cues. Treat the suggested files as a production convenience and keep editorial decisions with the creator or publishing team.

Color profiles, metadata, animation, and uncommon image features may change during browser decoding and re-encoding. JPG output is opaque; transparent source pixels are drawn onto white before encoding. PNG output retains canvas alpha where the browser supports it, but the validation and crop flow is designed for ordinary static RGB or RGBA comic images, not animated WebP, multipage files, HDR delivery, CMYK print separation, or archival masters. Use a dedicated image tool when those properties must be preserved exactly.

Only process work you own or are authorized to handle. A cropping utility does not grant rights to repost an episode, remove credits, split a paid chapter for redistribution, or bypass a platform’s access controls. Keep creator signatures and legally required notices intact. For client work, retain the approved source, delivery specification, and a checksum or archive of the final files. A reproducible handoff matters more than the convenience of any single crop setting.