tiff #

A Dart library for reading and writing TIFF and BigTIFF image files: tags and IFDs, strip/tile pixel data, common compression schemes, color conversion, and GeoTIFF/EXIF metadata — for files ranging from a few kilobytes to multi-gigabyte BigTIFF rasters.

Features #

• Classic TIFF (32-bit offsets) and BigTIFF (64-bit offsets), with automatic promotion to BigTIFF on write when the pixel data would exceed Classic's 4 GiB offset limit
• Full IFD/tag parsing, including every baseline TIFF 6.0 tag type plus BigTIFF's LONG8/SLONG8/IFD8
• Strip and tile pixel data, reading and writing (edge tiles are cropped on read and zero-padded on write automatically)
• Compression: None, PackBits, LZW, and Deflate/ZIP, read and write; CCITT Group 3/4 fax and JPEG, read only (see Limitations)
• Horizontal differencing predictor, read and write
• RGBA8 color conversion: WhiteIsZero/BlackIsZero, RGB(+alpha), Palette/ColorMap, CMYK, and non-subsampled YCbCr
• Brightness/contrast/gamma adjustment on decoded RGBA8 pixel data (ImageAdjustments)
• File-backed decoding that streams strips/tiles from disk instead of loading a whole file into memory (package:tiff/tiff_io.dart), plus region-of-interest decoding that skips chunks outside a requested crop
• TiffInitialView.forViewport picks a centered region and zoom level sized for a viewer's screen and decode budget, so a first frame never requires decoding a whole multi-gigapixel page
• TiffDisplayOptimizer.optimize rewrites a page as tiled (and optionally pyramided) RGB ahead of time, so a strip-organized and/or single-resolution source no longer forces a viewer to decode more than it needs to
• TiffChunkPlan plans memory-bounded, tile-aligned decode chunks for a page too large to decode whole, and TiffParallelDecoder.decodeBanded (package:tiff/tiff_io.dart) uses it to decode a page in bands across a pool of isolates — every budget/worker-count knob is a caller-supplied parameter, not something read from the OS
• Multi-page reading and writing via IFD chains
• GeoTIFF, EXIF, and GPS metadata parsing
• An optional package:image bridge (package:tiff/tiff_image_adapter.dart) for converting to/from image.Image and for decoding JPEG-compressed pages
• An optional Flutter minimap widget (package:tiff/tiff_minimap.dart, TiffMinimap) — a decode-agnostic overview-with-viewport-rectangle for panning/zooming a large page

Limitations #

• CCITT Group 3/4 fax (Compression 2/3/4) is decode-only. Virtually no modern software writes new Group 3/4 data, so encoding it isn't implemented.
• JPEG-in-TIFF (Compression 6/7) decoding requires the optional adapter (package:tiff/tiff_image_adapter.dart) — TIFF's baseline spec has no bundled JPEG codec, so this package borrows package:image's. Writing JPEG-compressed TIFF is not supported. Normally each strip/tile is its own self-contained JPEG (TIFF Technical Note 2) and only the strips/tiles a region actually touches get decoded; a page whose encoder instead split one continuous JPEG scan across chunk boundaries still decodes correctly, but any decodeRegion call against it costs as much as decoding the whole page — there's no way to decode part of one continuous scan.
• Only chunky (interleaved) PlanarConfiguration, and a single BitsPerSample value uniform across channels, are supported.

Getting started #

dependencies:
  tiff: ^0.5.0

Usage #

import 'dart:io';
import 'package:tiff/tiff.dart';

void main() {
  final bytes = File('image.tif').readAsBytesSync();
  final document = TiffDecoder.decode(bytes);

  for (final page in document.images) {
    print('${page.metadata.width}x${page.metadata.height}, '
        '${page.metadata.samplesPerPixel} samples/pixel');
    final raster = page.decode(); // raw samples, no color interpretation
    print(raster.sampleAt(0, 0, 0));
    final rgba = page.decodeRgba8(); // interleaved 8-bit RGBA
  }
}

For large (BigTIFF) files, decode directly from disk instead of loading the whole file into memory, and optionally decode just a crop:

import 'dart:io';
import 'package:tiff/tiff.dart';
import 'package:tiff/tiff_io.dart'; // dart:io-backed, not available on web

void main() {
  final document = decodeTiffFile(File('huge.tif'));
  try {
    final page = document.images.first;
    final crop = page.decodeRegion(TiffRegion(x: 0, y: 0, width: 512, height: 512));
    print(crop.sampleAt(0, 0, 0));
  } finally {
    document.close(); // releases the file handle
  }
}

For a viewer's first frame, decode a region sized for the screen instead of the whole page — TiffInitialView.forViewport picks a region centered on the page plus the zoom to display it at, capped by a decode budget you tune per device:

final page = document.images.first;
final initialView = TiffInitialView.forViewport(
  page.metadata,
  viewportWidth: 1080,
  viewportHeight: 2280,
  devicePixelRatio: 3.0, // from the platform, e.g. MediaQuery in Flutter
  maxDecodedPixels: 4000000, // lower this on memory-constrained devices
);
final preview = page.decodeRegionRgba8(initialView.region);
// Display `preview` scaled by initialView.zoom, then let the user pan/zoom
// further, decoding new regions on demand.

Preparing a file ahead of time so a later viewer never has to decode more than it needs to — this is a deliberate one-off rewrite, not something to run during interactive display, and it decodes the whole page into memory to do it (see the TiffDisplayOptimizer dartdoc for the memory caveat on a very large page):

final page = document.images.first;
final optimized = TiffDisplayOptimizer.optimize(
  page,
  mode: TiffOptimizationMode.tiledPyramid, // or .tiledOnly for just re-tiling
  tileSize: 512,
  minPyramidDimension: 512,
);
File('optimized.tif').writeAsBytesSync(optimized);
// optimized.tif is tiled RGB with progressively halved rungs appended as
// extra pages — open it the normal way and a viewer can decode by tile at
// whichever rung matches the current zoom, instead of the whole page.

Decoding a huge page in bands, bounded by a memory budget you choose and spread across a pool of isolates — the way to build something like a progressive viewer's own cache without decoding the whole page into memory or paying for redundant tile/strip redecoding at a tight budget:

import 'package:tiff/tiff.dart';
import 'package:tiff/tiff_io.dart'; // needed for TiffParallelDecoder

await TiffParallelDecoder.decodeBanded(
  filePath: 'huge.tif',
  pageIndex: 0,
  bandHeight: 256, // height of each delivered band
  maxBytesPerChunk: 200 * 1024 * 1024, // your own memory budget, however computed
  workerCount: 4, // your own choice — e.g. Platform.numberOfProcessors - 1
  onBand: (band) {
    // Called back on your isolate — write it out, feed a pyramid builder,
    // whatever you need. Bands from different workers can interleave.
    print('band at y=${band.y}, ${band.height} rows, ${band.rgba.length} bytes');
  },
);

Writing a TIFF:

import 'dart:io';
import 'package:tiff/tiff.dart';

void main() {
  final spec = TiffImageSpec(
    width: 256,
    height: 256,
    samplesPerPixel: 3,
    bitsPerSample: 8,
    photometric: TiffPhotometric.rgb,
    samples: myRgbSamples, // length == width * height * samplesPerPixel
    compression: 5, // LZW; see TiffTagId-style compression codes in the docs
    predictor: 2, // horizontal differencing (pairs well with LZW/Deflate)
  );

  final bytes = TiffEncoder.encode([spec]); // pass multiple specs for a multi-page file
  File('output.tif').writeAsBytesSync(bytes);
}

Reading GeoTIFF/EXIF metadata (present on the decoded page's metadata, no extra setup needed):

final metadata = page.metadata;
final geo = metadata.geoTiff; // null if the file has no GeoTIFF tags
if (geo != null) {
  print(geo.modelPixelScale); // [scaleX, scaleY, scaleZ]
  print(geo.geoKeys[GeoTiffKeyId.gtModelType]);
}
print(metadata.exifTags?[ExifTagId.dateTimeOriginal]?.asString());

Adjusting brightness/contrast/gamma on decoded pixels:

final rgba = page.decodeRgba8();
final adjusted = ImageAdjustments.apply(
  rgba,
  brightness: 15, // additive, sample units; negative darkens
  contrast: 1.2, // 1.0 = no change, around mid-gray
  gamma: 1.1, // 1.0 = no change; >1 brightens midtones
);

Optional: package:image bridge #

package:tiff/tiff.dart never depends on package:image — that stays a lightweight import for anyone who only needs raw TIFF pixels. Import package:tiff/tiff_image_adapter.dart as well to convert to/from image.Image, or to decode JPEG-compressed TIFF pages (Compression 6/7), which TIFF's baseline spec has no bundled codec for:

import 'package:tiff/tiff.dart';
import 'package:tiff/tiff_image_adapter.dart';

void main() {
  TiffImageAdapter.enableJpegSupport(); // needed once, only for Compression 6/7 pages

  final page = TiffDecoder.decode(bytes).images.first;
  final image = TiffImageAdapter.toImage(page); // an image.Image, ready for
  // cropping/resizing/PNG export/etc. via package:image

  final spec = TiffImageAdapter.toTiffImageSpec(image); // back to TIFF
  File('roundtrip.tif').writeAsBytesSync(TiffEncoder.encode([spec]));
}

Note: package:image is still a normal (if rarely large) entry in this package's pubspec.yaml — Dart has no per-file-optional dependency mechanism, so dart pub get fetches it for every consumer regardless of whether tiff_image_adapter.dart is ever imported. "Optional" here means your own code never has to touch package:image's API (or pay for importing it) unless you choose to.

Optional: Flutter minimap widget #

Every other entry point in this package works from plain Dart — no Flutter SDK needed. Import package:tiff/tiff_minimap.dart as well, from a Flutter app, for TiffMinimap: a ready-made overview-with-viewport-rectangle for panning/zooming a large page, driven by the same TransformationController an InteractiveViewer uses. It's decode-agnostic — hand it whatever already-decoded ui.Image overview bitmap and native page dimensions your own tiled/banded/isolate-based loading strategy already produces:

import 'package:flutter/material.dart';
import 'package:tiff/tiff_minimap.dart';

Widget buildMinimap(ui.Image? overview, int baseWidth, int baseHeight, TransformationController controller, Size viewportSize) {
  return TiffMinimap(
    overview: overview, // null shows a small placeholder spinner
    baseWidth: baseWidth,
    baseHeight: baseHeight,
    controller: controller,
    viewportSize: viewportSize,
  );
}

Note: unlike package:image, adding package:tiff/tiff_minimap.dart's flutter dependency to this package's own pubspec.yaml means a plain-Dart project (no Flutter SDK) can no longer depend on package:tiff at all, even if it never imports this entry point — Flutter SDK dependencies can't be made conditional the way a large but ordinary package like package:image can.

Example app #

See tiff_tester for a full Flutter app example built on this package.

Support #

If this package is useful to you, consider supporting its development on Ko-fi:

License #

Apache License 2.0. See LICENSE.