Converting images

Install with Composer · Packagist ↗

Optional module · pdftoolkit/pdf-images 0.1.7

English | Français

Optional PNG and JPEG file converters for the PDF image objects in PDFToolkit Core, for PHP 8.3 to 8.5.

The core represents PDF images, their colour spaces, samples, the /DCTDecode filter and transparency masks described by ISO 32000-1. This package interprets external file formats: PNG chunks and CRCs, scanlines, palettes, JPEG markers and frame components. An application that produces its own samples can use the core alone.

Installation

The package is available on Packagist. In your application:

composer require "pdftoolkit/pdf-images:^0.1"

The module uses roukmoute/pdf:^0.2 || ^0.3 || ^0.4 || ^0.5 || ^0.6, installed automatically by Composer. PHP 8.3 or newer on a 64-bit platform and the ctype, iconv and zlib extensions are required for this combination. The application's composer.lock records the selected versions and revisions. Installing the core alone does not install any converters. Shared documentation is available at PDFToolkit. The image module documentation contains its guides and API reference.

The same converters are compatible with core 0.6. Selecting the output PDF version and validating PDF 2.0 feature requirements belong to the core writer.

Explicit construction

use PDF\Document\Images\ImageXObjectFactory;
use PDF\Images\ImageFileBytes;
use PDF\Images\ImageImportLimits;
use PDF\Images\JpegImageReader;
use PDF\Images\PngImageDecoder;

// The application supplies bytes. No importer opens a path or URL.
$pngFile = new ImageFileBytes($pngBytes);
$jpegFile = new ImageFileBytes($jpegBytes);

// Each instance has its own limits, chosen for the application.
$limits = new ImageImportLimits(
    maxEncodedBytes: 1_048_576,
    maxDecodedBytes: 4_194_304,
    maxPixels: 1_048_576,
    maxDimension: 2048,
);

// PNG becomes a core SampledImage: colour and alpha are separate.
$samples = (new PngImageDecoder($limits))->decode($pngFile);

// JPEG becomes a core DCTImage: encoded data and PDF parameters.
$dct = (new JpegImageReader($limits))->read($jpegFile);

// The core composes the /Subtype /Image streams from table 89.
$factory = new ImageXObjectFactory();
$pngObject = $factory->create($samples);
$jpegObject = $factory->create($dct);

Add these streams explicitly to a page's /XObject resources, then paint them with an InvokeXObject operator and a matrix. The alpha mask is another greyscale PDF image object, referenced by /SMask. JPEG bytes remain unchanged with the /DCTDecode filter. The writer and document graph belong to the core; the converters have no singleton, global registry or page-building facade.

Supported formats

• Static, non-interlaced PNG with eight bits per component: greyscale, RGB, palette, greyscale with alpha and RGBA. All five scanline filters are reconstructed. Palettes are expanded to RGB; tRNS becomes an alpha mask.
• Baseline or progressive Huffman DCT JPEG with eight bits per component: greyscale, RGB and Adobe CMYK with transform zero. Required tables, frames and markers are checked; the PDF viewer decodes the DCT coefficients.

Animated or interlaced PNGs, other bit depths, embedded ICC profiles, YCCK JPEGs and ambiguous colour semantics are explicitly rejected. EXIF metadata does not cause automatic rotation. PNG gamma or chromaticity information does not create a calibrated colour space.

Checks and examples

The suite verifies expected samples and alpha, preserved JPEG bytes, generated PDF streams, CRCs, truncation and dimension, chunk and decompression limits. The contracts and limits describe each object.

The complete example builds a page containing four images and checkerboards that reveal transparency. Its original patterns are distributed under the MIT licence. Their Pillow generator is used only for development; the PHP package does not depend on Pillow or GD.

php examples/image-files.php output.pdf

See the changelog and security policy.

Guide source at the documented commit ↗