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Image DPI vs PDF page size: why your PDF page is huge

By DeckleUpdated

In Deckle, the size of a PDF page made from an image comes from the image's pixels, not from its DPI setting. With Match each image, one pixel becomes one point (1/72 inch), so a 2480 × 3508 pixel scan of an A4 page gives a page about 34 × 49 inches, whatever DPI the scanner wrote into the file. To get a real A4 page, choose Fit inside A4 in JPG to PDF, PNG to PDF or TIFF to PDF.

JPG to PDF

Size and sharpness are separate

Pixels

Image detail available

PDF page size

Physical reading or print dimensions

A DPI tag is not a page-size instruction

Conceptual comparison · inspect saved page dimensions and readable detail; a metadata tag alone cannot establish them.

Why pages come out huge or tiny

An image has two kinds of size:

  • Pixel dimensions, such as 2480 × 3508. This is the real detail in the image.
  • DPI (dots per inch), a tag that says how big the image should print. A 2480-pixel-wide image tagged 300 DPI is meant to print 8.27 inches wide, which is A4.

The DPI tag is only a suggestion stored in the file. Different apps write it differently, and many write nothing: phone cameras often record 72 DPI, screenshots carry whatever the system wrote, and editing an image can reset the tag without changing a single pixel. Two images with identical pixels can carry different tags.

Deckle ignores the tag and maps pixels to points. That keeps the result predictable: the same image always gives the same page.

The numbers

With Match each image, page size in inches is the pixel size divided by 72:

Image Pixels Page with Match each image
A4 scanned at 300 DPI 2480 × 3508 34.4 × 48.7 in
A4 scanned at 150 DPI 1240 × 1754 17.2 × 24.4 in
12-megapixel phone photo 4032 × 3024 56 × 42 in
Full HD screenshot 1920 × 1080 26.7 × 15 in
Small logo 300 × 100 4.2 × 1.4 in

The page size always comes from the original pixel dimensions. A photo over the device's pixel limit (16 megapixels on a computer or Android device, 4 megapixels on iPhone and iPad) is scaled down before it is stored, but its page stays the size it would have been at full resolution; only the embedded image has fewer pixels.

With Fit inside A4, every page is 595 × 842 pt (8.27 × 11.69 in) or the landscape equivalent. Images larger than the page, after margins, are shrunk to fit and centred. Images that already fit stay at one pixel per point and are centred, so the small logo above stays 4.2 inches wide on an A4 page. Nothing is enlarged or cropped.

How to get the page size you want

  1. Open the image tool for your format and add the images, or drop them onto the page.
  2. Under Page size, choose Fit inside A4 for anything that will be printed or read as a document.
  3. Choose Portrait or Landscape and a margin: None, Narrow (18 pt) or Standard (36 pt).
  4. Press Preview on a JPG or PNG row to see where the image sits on the page.
  5. Choose Create PDF. The checks on the result screen confirm each page has the planned size.

Keep Match each image when the PDF is for screens only and you want each page to fit its image exactly.

Does a big page mean better quality?

No. Detail depends on pixels, and Deckle keeps every pixel in both modes. A 300 DPI scan on a 34-inch page and the same scan shrunk onto an A4 page hold exactly the same image data. Zoom in on either and you see the same detail. The difference is only how large the page claims to be.

That matters when someone prints the PDF. A printer set to actual size cannot fit a 34-inch page on the paper; one set to fit the paper shrinks it. An A4 page prints at A4, and a 300 DPI scan on it prints at its real size and full sharpness.

When the page is too small

The opposite problem appears with small images. A 600 × 400 pixel photo is 8.3 × 5.6 inches with Match each image, and on an A4 page it stays at that size rather than filling the page. Deckle never enlarges an image, because enlarging cannot add detail and only makes pixels bigger. To fill more of the page, use a larger source image.

What about scanners that save DPI correctly?

Even a correct tag is ignored, so a properly tagged 300 DPI A4 scan still gives a 34-inch page with Match each image. This is why TIFF to PDF guides recommend Fit inside A4 for scanned paper: it puts the scan back on an A4 page. TIFF tags, including resolution, are not carried into the PDF. See how to convert a multi-page TIFF to PDF.

Tips

  • Pick Fit inside A4 for documents. It is the setting that matches paper.
  • Check the pixel size on the row. JPG and PNG rows show the image's pixel dimensions, which tell you how large the page will be with Match each image.
  • Do not change DPI to fix page size. Editing the tag changes nothing in Deckle; the pixels decide.
  • Use margins for printing. Narrow keeps the image clear of the printer's unprintable edge.

Frequently asked questions

Why is my scanned page enormous in the PDF?

Match each image was selected, which uses one point per pixel. A 300 DPI scan has about four times as many pixels per inch as a page has points, so the page comes out about four times the paper's width and height. Choose Fit inside A4.

Does Deckle read the DPI in my image?

No. Page size comes from pixel dimensions only.

Will Fit inside A4 make my image blurry?

No. The image is drawn smaller, but all its pixels are kept, so it prints sharply.

Can I choose Letter instead of A4?

No. The options are Match each image and Fit inside A4. Printers can fit A4 pages onto Letter paper.

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