Compression module

The Compress module reduces the size of the PDF file by applying a native macOS Quartz filter to the whole document. It acts mainly on the embedded images (resampling, recompression) and can produce a significantly lighter file without harming the readability of the content excessively. You reach this module from the Organization category of the Dashboard.

Principle

HtkPDF uses the Quartz filters built into macOS — the same mechanism the Preview application offers when you save a PDF with a filter. Several predefined profiles are available, each favouring a particular trade-off between visual quality and file size.

Available filters

The Compression options section offers four filters:

Reduce File Size

Quartz filter: Reduce File Size. This is the default choice. It resamples images to a resolution suited to on-screen use and applies moderate JPEG compression. Vector text and graphic elements are not affected. This is the option to choose in most cases.

Generic PDF/X-3

Quartz filter: Create Generic PDFX-3 Document. Produces a PDF conforming to the PDF/X-3 standard, intended for exchanges with a professional printer. The file size may increase — this filter is above all a conformance converter, not a compressor. Use it only to prepare a document intended for industrial printing.

Grey tones

Quartz filter: Gray Tone. Converts every color to greyscale, which significantly reduces the size (images are stored on a single channel instead of three). Choose it if you are sure the document does not need color.

Note: for a greyscale conversion without destructive recompression, prefer the dedicated Greyscale module in the Conversion category — it offers finer control over the conversion parameters.

Lightness decrease

Quartz filter: Lightness Decrease. Reduces the overall brightness of the document. This is a visual effect more than a compressor; it can be useful to save black ink on some types of laser printer.

Running the compression

Click the Compress button at the bottom of the sidebar. While processing, the button reads "Compressing…" and stays disabled. The operation runs in the background through the system Quartz engine; it can take a few seconds on a large document.

Once compression is finished, the compressed document replaces the working PDF in the view and a checkpoint is added to the History. The document moves into pending changes: to confirm the compression and keep the result, save the document explicitly through the Save button on the Dashboard (⌘S).

If applying the filter fails (missing Quartz filter, incompatible content), an error message is shown and the document stays unchanged.

Checking the effectiveness

To assess the gain concretely:

Before compressing, note the file size shown in the information area of the Dashboard;
Apply the filter, then save the compressed version to a separate file — Save (⌘S) always opens the save panel, give it another name;
Compare the size of the new file with the original one in the Finder.

How effective compression is depends heavily on the type of content:

PDFs loaded with images (photos, scans) can be reduced by 50% to 90% depending on the original resolution;
purely vector PDFs (text, shapes, generated graphics) gain little — text is already stored efficiently and compresses poorly.

Best practices

Keep the original: compression is destructive on images (resampling, JPEG recompression). If you plan to rework or reprint the document at high quality, keep an uncompressed copy.
Check quality after compression: zoom to 200% on pages containing text or detailed images to confirm that readability stays acceptable.
Combine with flattening if needed: if your document still contains annotations or layers, flattening it first can improve the compression ratio.
Do not chain several compressions on the same file: each pass adds quality loss without bringing any significant gain after the first.

Note: compression does not touch the document's metadata or digital signatures. If you distribute a compressed PDF, the author, title and date information stays as it is. To remove it, use the Scrub metadata module.

Screenshots

1 screenshot — click to enlarge