PNG to PDF or JPG to PDF: Which Should You Upload?
Short answer: it depends on what is in the image, and we measured both cases. A text form page converted to PNG came to 117,705 bytes while the same page as JPEG at quality 90 came to 122,358 bytes, so for forms and document scans PNG was smaller and stays crisp. The same test as a photograph flipped completely: PNG hit 2,916,465 bytes while JPEG at quality 90 was 124,851 bytes, about 23 times smaller. Wrap either one in a PDF and the conversion itself is lossless (about 868 bytes of page structure per image, verified by embedding a 1,149-byte JPEG and getting a 2,017-byte PDF). The rule: PNG for text, screenshots and forms; JPEG for photographs. The Image to PDF tool converts either format without re-encoding, so what you put in is what you get out.
Why does the answer depend on the content?
PNG and JPEG are optimized for different kinds of pixels. PNG is lossless and compresses by finding repeated patterns: large areas of exactly the same color, sharp edges between black text and white paper, straight lines in forms and tables. A scanned form is almost entirely flat white background with black glyphs, which is the best possible case for PNG, and it often ends up smaller than a JPEG of the same page.
JPEG is lossy and compresses by discarding detail the eye is less likely to notice: smooth gradients, subtle color shifts, photographic texture. A photo has thousands of slightly-different shades per area, which defeats PNG's pattern-matching (nothing repeats exactly) but is exactly what JPEG handles well. The same page content, rendered as a photo-like gradient, produced a 2,916,465-byte PNG versus a 124,851-byte JPEG at quality 90 in our test: a 23-times difference driven purely by the content type.
What do the numbers look like for a form or document scan?
We rendered an A4 page at 150 DPI with a title box, 24 form-field lines and checkboxes (flat black on white, the typical form), then encoded it four ways:
| Format | File size | Notes |
|---|---|---|
| PNG | 117,705 B | Smallest overall; glyph edges stay perfectly crisp |
| JPEG quality 90 | 122,358 B | Larger than PNG, with ringing artifacts around text |
| JPEG quality 80 | 103,758 B | Slightly smaller than PNG; light artifacts on thin lines |
| JPEG quality 60 | 88,128 B | Smallest, but glyph edges visibly fuzzy |
The counterintuitive result is the quality-90 row: the lossy format produced a larger file than the lossless one, because JPEG spends bits reproducing ringing artifacts around every sharp text edge that PNG does not have in the first place. This is why document scanners that offer a choice of output format should default to PNG for text: you get the smaller file and the more readable glyphs.
What do the numbers look like for photographs?
The same A4 canvas filled with a smooth gradient and fine detail (the photo case) flipped the result completely:
| Format | File size | Notes |
|---|---|---|
| PNG | 2,916,465 B | 2.9 MB: lossless has no patterns to exploit in continuous tone |
| JPEG quality 90 | 124,851 B | Visually indistinguishable from the PNG at screen size |
| JPEG quality 80 | 76,779 B | Practical sweet spot for photos inside documents |
| JPEG quality 60 | 46,299 B | Noticeable softening of fine detail |
A 23-times size difference at quality 90 is the whole argument for JPEG when the content is photographic. If your scan or photo upload contains pictures, headshots, product shots or any continuous-tone image, encoding as PNG wastes megabytes for no visible benefit at normal viewing size.
Does converting to PDF change the quality?
No. Converting an image to PDF wraps it in a page structure; it does not re-encode the image data. We verified the overhead directly: a 1,149-byte JPEG embedded in a minimal PDF produced a 2,017-byte file, meaning the page structure (catalog, page tree, content stream, cross-reference table) added about 868 bytes, and the image bytes were copied unchanged. A 117 KB PNG becomes roughly a 118 KB PDF page; a 125 KB JPEG becomes roughly a 126 KB PDF page.
The same applies in reverse: extracting the image from the PDF returns the original bytes. This is also why the question "does JPG to PDF reduce quality" has a firm no: the JPEG inside the PDF is the exact JPEG you started with, bit for bit. Quality loss in the pipeline can only come from re-encoding the image itself (changing its format or quality level), which a plain conversion step does not do.
Which should I upload for an online form or portal?
Work through it in this order:
- Use PDF if the portal accepts it. PDFs preserve page order and layout across multiple pages, which a pile of loose images does not. Multi-page submissions (a form plus supporting pages) should always be one PDF.
- Pick the image format by content. Text, forms, screenshots and line drawings: PNG (smaller and sharper, as our test showed). Photographs and continuous-tone scans: JPEG at quality 80 to 90.
- Check the size cap before uploading. Portals typically cap uploads between 1 MB and 10 MB. If your PDF exceeds the cap, compress the source images with an Image Compressor first, then reconvert, rather than dropping JPEG quality to a level where text becomes hard to read. Our guide to exact pixel and KB targets for photo uploads has the specific numbers for common portal requirements.
- Convert with a lossless step. The Image to PDF tool embeds images without re-encoding them, so the PDF contains exactly the PNG or JPEG bytes you selected.
What are the honest limits?
- Mixed-content pages split the difference. A page that contains both a photograph and a text table is not ideal for either format alone: PNG will be large because of the photo, JPEG at low quality will soften the text. The practical fix is JPEG at quality 80, which keeps text readable while controlling size, or splitting the page content if the source allows it.
- These are one-content-type tests, not every image. We measured one form-style page and one photo-style page rendered at A4 150 DPI. Real scans vary: a mostly-blank page with a small photo will behave closer to the form case; a full-page photo scan behaves like the photo case. The direction of the result (text favors PNG, photos favor JPEG) is a property of the formats themselves and holds across content, but the exact byte counts shift with your page.
- 150 DPI is a screen-and-email resolution. Print submissions often want 300 DPI, which quadruples the pixel count and roughly quadruples file sizes in both formats. If a portal demands 300 DPI and a small size cap, JPEG at quality 80 becomes the only viable option for photographic pages.
- Conversion cannot fix a bad source. A blurry photo or an under-resized screenshot stays blurry inside the PDF. The format choice controls size and compression artifacts, not capture quality.
- Some portals re-encode your upload. A few systems convert uploaded PDFs to images on their end for preview, at their own quality settings. If your carefully-prepared file looks worse in the portal's preview than on your machine, the portal's re-encoding is the cause, not your conversion.
What did we actually test?
We rendered two A4 pages at 150 DPI in headless Chrome on a Windows machine (2026-10-26) using the canvas API: one form-style page (title box, 24 text field lines with underlines, checkboxes, flat black on white) and one photo-style page (full-page gradient with soft radial shapes and fine detail, simulating continuous tone). Each canvas was encoded to PNG and to JPEG at quality levels 90, 80 and 60, and the byte counts above are the literal sizes from that session. The PDF wrapper overhead figure comes from a separate minimal-PDF construction: a 1,149-byte JPEG embedded as a DCTDecode image XObject produced a 2,017-byte PDF, confirming the image was copied unchanged and the structure added about 868 bytes.
What this test does not cover: it uses two synthetic pages rather than scans from specific devices, and it measures size and structure, not perceptual quality scores. Different page content (denser text, different photo subjects) will shift the absolute byte counts, but the qualitative findings (PNG wins for flat text, JPEG wins for continuous tone, PDF conversion is lossless) follow from how the formats work and are consistent across content types. JPEG artifact visibility is subjective; our quality descriptions reflect what is visible at 100 percent zoom on a standard display.
Quick FAQ
Should I upload PNG or PDF for an online form?
Upload a PDF when the portal accepts it, because PDFs preserve page order and layout across multiple pages. Whether the images inside that PDF should be PNG or JPEG depends on the content: our tests showed a text-form page as PNG came to 117,705 bytes while the same page as JPEG at quality 90 came to 122,358 bytes, so PNG was actually smaller for text. For photographs, JPEG was about 23 times smaller. Match the image format to the content, then wrap it in PDF.
Does converting PNG to PDF make the file bigger?
Only by a small fixed overhead, not by re-encoding the image. A PDF wraps each image in a page structure (catalog, page tree, cross-reference table) that added about 868 bytes in our single-image test: a 1,149-byte JPEG embedded in a PDF produced a 2,017-byte file. The image data itself is stored unchanged, so a 117 KB PNG becomes roughly a 118 KB PDF page. The format conversion does not shrink or inflate the image.
Does converting JPG to PDF reduce quality?
No, conversion is lossless. The JPEG bytes are copied into the PDF exactly as they are, with no re-encoding, so the image you get out is identical to the image you put in. Quality loss only happens if you re-encode the image (changing its JPEG quality level) before or during conversion. If you convert an already-compressed JPEG to PDF and back, the round trip is byte-for-byte the same image.
Which is better for scanned documents, PNG or JPEG?
For text documents and forms, PNG: our test page (A4 at 150 DPI with text and field lines) was 117,705 bytes as PNG versus 122,358 bytes as JPEG at quality 90, and the PNG keeps glyph edges crisp because flat black-on-white text is exactly what lossless compression handles well. For photographs or pages with continuous-tone images, JPEG: the same test photo was 2,916,465 bytes as PNG versus 124,851 bytes as JPEG at quality 90.
What JPEG quality should I use for scanned documents?
Quality 80 is the practical sweet spot for photographs inside documents: our tests showed quality 90 and quality 80 both keep text readable while quality 80 cuts file size noticeably (the photo test dropped from 124,851 bytes at q90 to 76,779 bytes at q80). Below quality 60, ringing artifacts around text glyphs start to blur thin strokes, which matters for documents that a human or an OCR system must read later.
Can I convert images to PDF without losing quality?
Yes, the conversion itself is lossless: images are embedded in the PDF exactly as they are, with only a small wrapper overhead (about 868 bytes per image in our test). Any quality loss in the pipeline comes from the image's own format, not from the PDF step: a JPEG stays as lossy as it was, a PNG stays lossless. To keep quality high, start with PNG sources (or high-quality JPEG) and avoid re-encoding during conversion.
Need the PDF under a portal's size cap after converting? Our PDF Compressor re-saves the whole document at a lower DPI, and if the source images still need trimming first, the Image Compressor handles that in the same browser session.