A pixel in a JPEG is three numbers: red, green, blue, each 0–255. But "red = 255" is meaningless without a reference: which red? A 6500 K daylight pure red? An LED-monitor primary at 615 nm? The an…
The math behind embedding a JPEG into a PDF page is straightforward arithmetic, but it routinely confuses people because two intuitions about DPI fight each other. The first intuition: "300 DPI is …
Open a JPG on a phone and you see it the right way up. Open the same file on an old Windows machine and it's lying on its side. The pixels haven't changed — the difference is whether the viewer res…
A common surprise: upload a 5 MB JPEG, get a 5 MB PDF. Some tools market "fast PDF" or "compressed PDF" output and the natural expectation is that the result should be smaller. The output's size is…
When you drop several photos into JPG2PDF, what comes out is one PDF with one page per photo. This article covers the practical details: page order, page size, what's preserved from each JPEG, and …
The most counterintuitive thing about JPG-to-PDF is how little re-encoding actually happens. The existing JPEG stream goes into a PDF Image XObject with a /Filter /DCTDecode declaration, told to li…
"JPEG quality" is a 0–100 number that appears in every photo encoder and almost no two tools mean the same thing by it. The number is not a percentage of preserved information; it is not a quality …