> On Dec 2, 2021, at 9:26 AM, Hammer, Erich F <[log in to unmask]> wrote:
> Ah!  I didn't consider that it might be an SVG, although I suspect that is only a slim possibility.  Technically, you don't enlarge an SVG but just scale it.

Well, the question was about JPEG and PNG, so it’s fair to assume it wasn’t an SVG.

That was part of why I said I wasn’t sure about PNGs, as I wasn’t sure exactly what was in them.  It looks like it’s just raster, no vector data, but there’s support for arbitrary headers, so I guess someone could have a way to specify masks and regions of interest.  (Most people just add an alpha channel for a single transparency mask, but with all of the AI/computer vision stuff these days, I could see a use for multiple masks)

PostScript and EPS (Encapsulated PostScript) used to be the main vector formats back when when ‘the web’ was new.  Of course, we also had to worry about fixed sized fonts and other headaches that are mostly gone these days.

PDFs can also be scaled, but they’re a weird hybrid as you can insert raster images in them. (And I often downsize images depending if they’re intended to be shown on a screen instead of printed, to get my file size down)

JPEG 2000 is also a weird beast— it uses wavelet compression, and there’s an API to you can send out a varying amount of data based on what resolution it’s being rendered at, or if you’re only looking at a portion of the image.  So it’s useful for storing large images that someone might say to analyze subsets of, like in science and medical imaging, or maybe high-res scans of artwork, as you don’t need to pre-generate multiple resolutions of tiles like if you were if you taking a Google Maps type approach to serving your data.

But there isn’t universal browser support for it, so you need to have some sort of middleware to generate regular JPEGs on demand.


The Encyclopedia of Graphics File Formats is a great read if you want to know way more than most people would need to know about image formats, but it’s 25 years old at this point, so doesn’t include JPEG2000 and the various attempts to make animated PNGs.  Or Kodak PhotoCD, as it just had an page that was basically ‘Kodak said they’ll sue us if we reverse engineer it’

(I was making web pages back in the days before HTML+ and Netscape, so we still had to get a lot of our information in dead tree form)

You can also check LoC’s, which has both detailed information about formats including links to the official specifications if they’re open specs, as well as articles to help people select a format for digital archiving efforts.


/former webmaster of
//has been doing this for way too long