Image to PDF

Making a PDF from photos or scans

1. Choose your images or drop them on the box. JPG, PNG and WebP all work; anything the browser reports as a non-image is ignored without an error message.
2. Each file appears in a numbered list. The arrow buttons move a page up or down by one position and the cross removes it. Page 1 in the list is page 1 of the PDF.
3. Pick a page size (A4, US Letter or "Fit to image") and a margin (None, Small or Large).
4. Press "Create PDF". When the status line says "Done", the file has been saved as images.pdf in your downloads folder.

Selecting files again adds to the list rather than replacing it, so you can gather pictures from several folders. Files are listed in the order they were added; select in the order you want, or fix it afterwards with the arrows.

How the page layout is calculated

The three margin options are 0, 24 and 48 points. A point is 1/72 of an inch, so "Small" is a third of an inch (about 8.5 mm) and "Large" is two thirds of an inch. A4 pages are 595.28 by 841.89 points (210 by 297 mm) and US Letter pages are 612 by 792 points.

With A4 or Letter, every image is scaled by the same factor on both axes so it fits inside the page minus the margins, then centred. The factor is the smaller of (usable width / image width) and (usable height / image height). The aspect ratio never changes and nothing is cropped. Small images are enlarged to fit too, which can make a low-resolution picture look soft.

Worked example: a 4000 by 3000 pixel landscape photo on A4 with the Small margin. The usable area is 547.28 by 793.89 points. The width ratio is 0.1368 and the height ratio is 0.2647, so the smaller one, 0.1368, wins. The image is placed at 547.28 by 410.46 points, centred, with blank space above and below. Because 4000 pixels cover about 7.6 inches, the printed resolution is roughly 530 pixels per inch, far more than needed for sharp printing.

"Fit to image" works differently. Each page is sized to its own image, using 0.75 points per pixel (the usual 96-pixels-per-inch screen convention), plus the margin on every side. A 1200 by 800 pixel image with the Small margin gives a page of 948 by 648 points. Pages in this mode can therefore have different sizes within one PDF.

What goes into the file

Each image is drawn onto a canvas with a white background and saved again as a JPEG at 92 percent quality. That JPEG is embedded in the PDF unchanged, one image per page. Two consequences follow. Transparent areas in PNG or WebP files become white. And the resulting PDF is usually close to the combined size of the re-encoded pictures, so a stack of large phone photos produces a large PDF.

The PDF itself is written directly by the page: a catalogue, a page tree, and for each page one image, one drawing instruction and one page entry, followed by a cross-reference table. It is a plain, simple structure that any PDF reader, printer or upload form should accept. It contains no text layer, so you cannot select or search the words in a scanned page.

Where this is useful

• Turning a handful of phone photos of a signed form into one attachment for an email.
• Bundling receipts for an expense claim, in date order.
• Submitting ID or proof-of-address images to a portal that wants a single PDF.
• Making a quick portfolio or lookbook from exported images.

Tips and limits

• Use "Fit to image" with margin "None" when you want a PDF that looks exactly like the pictures, such as a comic or a slide export.
• Use A4 or Letter when the PDF will be printed, so every sheet comes out the same size.
• If the PDF is too large to email, resize or crop the photos beforehand; this tool does not downscale them, it only re-encodes at 92 percent.
• If a file cannot be decoded, creation stops with "Could not read" and the name of that file. Remove it from the list and try again.
• Formats such as HEIC are not decoded by most desktop browsers, so convert them to JPG first.

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