PDF to JPG or PNG: choosing the resolution
Image en PDF editorial team ·
Converting a PDF to an image means rendering it at a precise pixel size. The resolution you choose decides that size, and therefore both the sharpness and the weight of the file.
What DPI means here
The converter multiplies the page dimension by the chosen resolution, divided by 72 (the PDF point). An A4 page of 595 × 842 points therefore gives 595 × 842 pixels at 72 DPI, 1240 × 1754 at 150 DPI and 2480 × 3508 at 300 DPI. The page is really rendered at that scale, not merely labelled with another value.
150 DPI is the default compromise: readable on screen, enough for most office printing, with reasonable file sizes.
PNG or JPG
PNG is lossless: every pixel is recorded exactly. On a page of text, a table or a chart, edges stay sharp and flat colours stay even. It is the choice to prefer for documents.
JPG compresses with loss. On a photographic page it gives clearly lighter files for a small visual difference. The quality setting only appears when you choose JPG: the higher it is, the larger and more faithful the file.
What an image loses
A page rendered as an image no longer contains selectable text, links or vectors. It therefore allows no search, no copy and no enlargement without loss. If those uses matter, keep the PDF alongside the images.
Memory and practical limits
Each rendered page takes memory during the operation: at 300 DPI an A4 page needs about 8.7 million pixels, close to 35 MB of memory for the canvas. A document of several hundred pages at that resolution can exceed what the browser allows.
The converter processes pages one by one, accepts up to 200 pages per document and refuses a page whose render would exceed 80 megapixels or 16,384 pixels on a side. In that case, lower the resolution or convert a range of pages at a time.