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Grzegorz MartensandClaude Opus 5.5
ea6c329731
decode_jbig2 sits next to decode_ccitt, through hayro-jbig2 as Export ▸ Images used it, and shares CCITT's row sink. The JBIG2 page has to be the image's size: PdfCraft's renderer draws the whole page into the image (black box: a 4-row page behind /Height 2 fills the image box with all four rows), so the rows of a taller page aren't the image's. The decoder decodes a page whole, so the page is checked before it is decoded: that size, within the caller's bound as rows of one bit, and at most 2^28 pixels (MAX_JBIG2_PIXELS; the decoder keeps a bit a pixel, about 34 MB there). Document::decoded_image_within decodes a JBIG2 image as it does a fax image: the filters before it undone first, then the decoder with the /JBIG2Globals of the image's own /DecodeParms entry (/Crypt counts in the position; fax_params and the globals now share last_filter_parms). Globals have a limit of their own, MAX_JBIG2_GLOBALS (32 MiB, moved from Export), and globals that can't be read are an error rather than ignored. Export ▸ Images reads JBIG2 through it, so its own decoder, row sink and DecodeParms reader go, and hayro-jbig2 leaves pdfcraft-create. JBIG2 behind another filter now exports, and so copies (Copy Image uses the same function); a page taller than the image, which Export cut to the image's rows, now skips the image, as one of another width did. doc_export_all_images' description no longer lists JBIG2 inside other filters as skipped. The optimizer's monochrome step read images through decoded_image_within and relied on JBIG2 failing there: it now leaves JBIG2 images alone explicitly, as before (a resampled one would come out Flate under Retain), and the README and parity note list them as not yet handled. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
48 lines
3.8 KiB
Markdown
48 lines
3.8 KiB
Markdown
# pdfcraft-create
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Layer L4. Create a PDF (Acrobat's Create a PDF tool), execution plan M10.2:
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- `blank(width, height, pages)`: an empty document;
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- `from_images(&[(name, bytes)])`: one page per image, sized from the image's resolution
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(PNG `pHYs`, JPEG JFIF density; 72 dpi when absent). JPEG data is embedded as is
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(`/DCTDecode`, grey, RGB or Adobe-inverted CMYK); PNG is decoded and stored with Flate,
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with transparency as a soft mask. A picture of only pure black and white (a 1-bit PNG or TIFF,
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eight-bit grey, a two-colour palette, RGB without a profile) is stored at one bit per pixel, as
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CCITT Group 4 or Flate, whichever is smaller as stored (`pdfcraft_filters::encode_g4`). An ICC profile in the file (JPEG `APP2 ICC_PROFILE`, PNG
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`iCCP`) that matches the image's colour space is kept as an `/ICCBased` colour space with
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the device space as `/Alternate`; images with the same profile share one profile object.
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JPEG metadata scanning skips marker fill bytes and reads application segments after the
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frame header, stopping at the first scan or end marker. Broken or mismatched ICC profiles
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still fall back to the device colour space;
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- `from_images_with_resolution(images, ImageResolution::Dpi(dpi))`: override the page
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resolution (1–1200 dpi), without resampling or recompressing image pixels. Use 72 dpi
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for one point per pixel, or `ImageResolution::Embedded` for the same behavior as
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`from_images`. The largest page side is still capped at 14,400 points;
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- `from_text(text, …)`: plain text set in Helvetica, wrapped and paginated. Text Helvetica
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can't draw is refused, naming the line and the character, never set as `?`.
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- `from_text_escaped(text, …)`: the same for reports PdfCraft generates from documents
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(comment summaries, compare reports): such characters are written as `[U+XXXX]` and the first
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line says so (`ESCAPED_NOTE`).
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Every function returns a `pdfcraft_cos::Document`; the caller writes it.
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Image export and Save Image As apply each lossless image's Decode pair before converting its color components.
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JBIG2 images and masks are decoded through `pdfcraft_cos::Document::decoded_image` (`pdfcraft_filters::decode_jbig2`), behind
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other filters too, with the `/JBIG2Globals` of their own `/DecodeParms` entry, as `JBIG2Decode` gives them: black as 0. An image
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whose JBIG2 page isn't its size (PdfCraft's renderer draws the whole page into the image; the page is refused before it is decoded),
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or whose globals can't be read or decode to more than 32 MiB (they are decoded before the page's size is known, so they have a
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limit of their own), is skipped; such a mask is left out and the image exported opaque, as JPX and CCITT
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masks are.
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Indexed Decode values select palette entries after rounding and clipping. Color-key masks compare the original samples.
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Missing, null or malformed Decode arrays keep the default mapping.
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Soft-mask Decode intervals map samples to opacity before the mask is resized, including reversed ranges and indirect entries.
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The existing 16-bit path still uses each sample's high byte.
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JPEG image Decode handling remains limited.
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ICC transforms and calibrated color conversion remain outside this export path.
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CCITT fax images (Group 3 and 4) are decoded for export through `pdfcraft_cos::Document::decoded_image` with their
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`/DecodeParms` (`/Columns` has to be the image's width; up to `/Height` rows, whatever `/Rows` says), behind other filters such as
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`ASCII85Decode` too. Byte-aligned Group 3 rows are read by their end-of-line codes, whether the fill starts each code on a byte or
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ends it on one, when the data starts with one (T.4 sends one before the first row), and on bytes otherwise, whatever `/EndOfLine`
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says; data that comes up short is reported. Data with codes but none before the first row is read on bytes, and is reported or,
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at `/K 0`, may come out wrong. JPEG 2000 images are still reported, not exported.
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