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Image formats

PNG vs JPG for diagrams and line art

By DeckleUpdated

For diagrams, charts, logos and line art, PNG is the better format: it keeps every pixel exactly, so thin lines and small labels stay crisp, while JPG blurs their edges. Export the diagram as PNG and convert it with PNG to PDF. Keep JPG for photographs, where its compression is invisible and the files are much smaller.

PNG to PDF

Choose a source for the job

Photograph

Inspect colour and detail

Diagram

Inspect lines and labels

Scan

Inspect frames and text

A static PDF page does not preserve motion

Conceptual illustration · image format and output page behaviour are separate decisions.

PNG vs JPG at a glance

PNG JPG
Compression Lossless: every pixel kept Lossy: fine detail discarded
Sharp edges and thin lines Crisp Soft, with halos
Flat areas of colour Clean, and compress well Can show blotches and block edges
Transparency Yes No
Photos Large files Small files, no visible loss
In a Deckle PDF Pixels kept exactly by PNG to PDF Copied unchanged by JPG to PDF

Why line art suits PNG

Line art is made of hard edges: a one-pixel line, the outline of a box, the stroke of a letter in a label. JPEG compresses an image by smoothing detail in small blocks, which is exactly what destroys a hard edge. The line gets a faint grey haze either side, and flat colour areas pick up mottled noise. Why JPG makes text blurry explains the mechanism.

PNG uses lossless compression that works by finding repetition. A diagram with large areas of one colour and clean edges is full of repetition, so it compresses well while staying identical. That is why a flowchart exported as PNG is often smaller than the same flowchart saved as a high-quality JPG, and sharper too.

Typical line-art images that belong in PNG:

  • Flowcharts, org charts and process diagrams
  • Charts and graphs exported from a spreadsheet
  • Floor plans, wiring diagrams and technical drawings
  • Logos, icons and signatures
  • Screenshots of software, spreadsheets and documents

How to put diagrams into a PDF with Deckle

  1. Export each diagram from its app as PNG, at the size you want to read it.
  2. Open PNG to PDF and choose Select files, or drop the PNGs onto the page.
  3. Put them in order with the up and down arrows.
  4. Choose Fit inside A4 for printing, or Match each image to give each diagram its own page size.
  5. Choose Create PDF, then zoom in on the smallest label to check it is sharp.

PNG to PDF stores the pixels exactly, with transparency kept. How to convert PNG to PDF covers ordering a diagram set and choosing page sizes.

Export at a useful size

PNG keeps every pixel, but it cannot add pixels that are not there. A chart exported at 800 pixels wide stays 800 pixels wide in the PDF; printed across an A4 page, its labels look rough. Export larger instead:

Diagram will be Export at least
Read on screen The width of a typical screen, about 1600 px
Printed on A4 About 2480 px wide (300 pixels per inch across 8.27 inches)
Printed small, within a page Enough for 300 pixels per inch at its printed size

Each page keeps up to 16 megapixels on a computer or Android device, and 4 megapixels on iPhone and iPad. A larger PNG is scaled down to fit and stays a PNG, but thin lines can soften, so export diagrams within the limit when you can. PNGs above 64 megapixels, or 25 megapixels on iPhone and iPad, are refused.

When the diagram is not an image

If your diagram comes from an app that can export PDF or SVG directly, that is often better still: the lines stay vector, sharp at any zoom, and text stays selectable. Use PNG to PDF when you only have images, or when you need to combine exports from several apps into one document.

When to use JPG instead

Use JPG for photographs and for images with photographic content, such as a product photo or a scanned colour illustration. There, JPG looks the same as PNG at a fraction of the size. A diagram that contains a photo is a judgement call: if the labels matter most, use PNG.

Tips

  • Never save a diagram as JPG and then as PNG. The blur from the JPG stays; PNG only preserves it.
  • Keep transparent backgrounds deliberate. Transparency is kept in the PDF and usually shows as white. See PNG transparency in PDF.
  • Use standard PNGs. Animated, interlaced and 16-bit PNGs are refused by PNG to PDF; re-save as 8-bit.
  • Export PDF pages as PNG too. To turn a PDF diagram back into an image, PDF to PNG keeps lines sharper than JPG.

Frequently asked questions

Is PNG or JPG better for diagrams?

PNG. It keeps edges and small text exactly, while JPG softens them.

Why is my PNG chart smaller than the JPG version?

Charts have large flat areas that lossless compression handles very efficiently. JPEG spends space on detail a chart does not have.

Does PNG to PDF change my diagram?

No. The pixels are kept exactly and stored with lossless compression.

Should I use PNG for photos too?

Not usually. Photos are much larger as PNG with no visible gain. Use JPG to PDF for photos.

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