Case study
Case study: one photo, four ways, from 19 KB to “too large”
How image format and size changed a one-page PDF from 19 KB to rejected, with exact numbers.
Photos are the main reason PDFs become large and slow. We built a one-page site-visit report with a heading, two short paragraphs and a single photo of a building elevation, then embedded that photo four different ways.
Results
| Image embedded as | HTML size | Result | PDF size | Time |
|---|---|---|---|---|
| PNG, 2400×1800 (4.1 MB file) | about 5.5 MB | Rejected: request too large | none | none |
| JPEG, 2400×1800, quality 90 (789 KB) | 1.05 MB | Converted | 807 KB | 2.1 s |
| JPEG, 1200×900, quality 80 (124 KB) | 166 KB | Converted | 143 KB | 0.8 s |
| SVG illustration | 14 KB | Converted | 19 KB | 0.5 s |
Times are the full round trip from our test machine, including upload.
What happened
- The PNG never reached the converter. Images embedded as data URLs are base64 text, about a third bigger than the file. A 4.1 MB PNG became roughly 5.5 MB of HTML, over the 2 MiB HTML and 3 MiB request limits.
- The full-size JPEG was embedded almost byte for byte. An 807 KB PDF for one page is mostly the photo. At 2400 pixels wide, it has far more detail than a page 190 mm wide can show (about 300 pixels per inch at that width needs only around 2,250 pixels).
- Halving the dimensions cut the PDF by 82% (807 KB to 143 KB) and the conversion time by more than half, with no visible difference at normal zoom.
- Vector graphics were tiny and stay sharp at any zoom, but only suit diagrams and illustrations, not photographs.
Practical sizes
- Full-width photo on A4 or Letter: 1,200–1,600 pixels wide looks sharp on screen and in office printing.
- Half-width or thumbnail: 600–800 pixels.
- Use JPEG (or WebP) for photos, PNG only for screenshots and graphics with flat colour, SVG for logos and charts.