Thursday, November 18, 2021

Forgotten Image Formats

Ernie Smith (via Gus Mueller, Hacker News):

Around this time 30 years ago, two separate working groups were putting the finishing touches on technical standards that would come to reshape the way people observed the world. One technical standard reshaped the way that people used an important piece of office equipment at the time: the fax machine. The other would basically reshape just about everything else, becoming the de facto way that high-quality images and low-quality memes alike are shared on the internet and in professional settings. They took two divergent paths, but they came from the same place: The world of compression standards. The average person has no idea what JBIG, the compression standard most fax machines use, is—but they’ve most assuredly heard about JPEG, which was first publicly released in 1992. The JPEG format is awesome and culture-defining, but this is Tedium, and I am of course more interested in the no-name formats of the world.

Are TIFF, BMP, and PCX really considered to be forgotten?

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TIFF is certainly still used for Pro applications. If you want an uncompressed, widely supported format, this is it. PNG is compressed and slower.
BMP, I don't know. It's a Windows format and it's been a while since I've used one, being a Mac person.
PCX, well this does bring up memories of the 90ies, it was very popular back then.

AFAIK, TIFF supports multiple representations but PNG doesn’t. And TIFF has better black-and-white compression for saving scanned documents in PDF files.

I thought BMP was still used by favicon.ico files.

TIFF is definitely still used for scientific images, particularly support for multiple images, e.g. for microscopy.

And just last week, I got X-ray images in BMP format from the vet. But that just means the software may be a bit ancient? Or is that that the absence of compression that makes it some kind standard for X-ray machines?

Kevin Schumacher

I remember BMP from my Windows days. For a while I think it was the default format for Microsoft Paint. I have no idea whether it's still popular, though.

TIFF was never a really consumer format, from my recollection.

And I still don't even know what PCX is, despite using computers since the Apple ][ GS and being online since the mid-'90s.

PCX was really good for 1-bit black and white art but is indeed largely forgotten. Though I do think I still have some legacy logos saved in that format.

Earlier commented is correct that TIFF was really never a well known format with average consumers but many, me included, use it all the time with the Adobe suite. They’re smaller than PSD native format which makes them fine for flattened images.

And TIFF apparently is not dead with Apple. I’ve observed that images pasted into e-mail sometimes end up as TIFF. Other times PNG. Not really sure what makes choose one over the other at different times.

Kevin Schumacher

Unrelated to the overall discussion, but to add on to your anecdote about Mail image formats, when using AirDrop to send screenshots (specifically those, not photos) from my iPhone to my Mac, sometimes they come through as JPG and sometimes as PNG. I have no idea what the difference is there, either.

> I thought BMP was still used by favicon.ico files.

.ico are icon files, so they contain multiple representations. What they contain is more or less raw bitmaps in a variety of formats, but not completely. .cur are cursors using almost the same format, except it has a way to specify where the "point" is and also to make the opaque pixels invert/XOR what they cover, and .ani is a format for animated cursors, which is apparently a completely different, unrelated format.

TIFF is still around... it's what's on our multi-function scanners at work instead of PNG. Including a multipage format everything balks at when opening.

And Windows still likes mentioning BMP in image apps.

PCX I haven't seen since the 90s.

I converted my images to JPEG 2000, assuming it would take off, but it never did. QuickTime has stopped supporting it. So recently I converted them to HEIC. I wonder if it will ever succeed either.

The reality is that for someone born in 1998 - i.e. a college grad with a job -- who would have started using computers in their teens in the 2010s, I can't think of anything that would have led to them encountering BMP or PCX files. If they appears=ed at all, it would be one of the arcane formats in a drop-down box that you'd never bother with, the same way I used to ignore PICT files in the early 00s.

sometimes they come through as JPG and sometimes as PNG. I have no idea what the difference is there, either.

Sounds like it’s encoding as both and using whichever is smaller. Or it’s analyzing the image for characteristics such as “how broad a range of colors does this use” and deciding based on that (but, again, with the goal of sending whichever one is smaller).

I converted my images to JPEG 2000, assuming it would take off, but it never did.

It’s kind of funny how JPEG kept trying to do a version 2. JPEG 2000, JPEG XR (a.k.a. Windows Media Photo), LS/XL/XS/XT…

So recently I converted them to HEIC. I wonder if it will ever succeed either.

Well, unlike JPEG 2000, Apple itself uses HEIC extensively, as the default format for photos taken on an iPhone. So I expect a built-in decoder will stick around for easily two decades. For encoding, it’s possible Apple will eventually move to JPEG XL. They might also move to AVIF. Most likely, though, they’ll wait for H.266 or 267 and derive another HEIC-like format from that, about a decade from now.

There's a truckload of old image formats, Wikipedia has a list:

One that is still current but very niche is DICOM, which is used for medical imagery, e.g. X-Rays or MRIs. I am also partial to DjVu, which is meant to compress black & white scans, e.g. books, and is dramatically more efficient than whatever PDF uses, by orders of magnitude.

I've never heard of PCX, and BMP reminds me of software image assets in Windows 95. TIFF strikes me as an old reliable, I've used that format in the internet era and consider it a valid choice for some people, but personally I'd use PNG over it any time.

IIRC Tiff uses LZW compression. PNG uses deflate (used by zip), but adds other tricks like copying other parts of the image to the current location.

Last time I coded image manipulating software for the Mac, TIFF was the internal format used by Cocoa/CoreImage. That could well still be the case.

Non-lossy image formats like TIFF and PNG compress better than JPEG on images with sharp edges: JPEG uses the DCT transform, keeping low frequency components, and discarding high frequency components. That works for natural images, but not for text for instance. PDF uses a JPEG variant internally.

DjVu is fun, using lossless compression for text and lossy compression for images. IIRC, it was developed by Yan Le Cun of Convolutional Neural Network renown. Unfortunately it didn't take off, like so many other things.

My question is: Why aren’t JPEGs forgotten?

I mean the vast majority of people have for extensions hidden. Probably they don’t know that their iPhones aren’t JPEGs anymore.

My guess is that people just think of JPEG as pictures, the same way they think of animations as GIFs and music as MP3. The actual format doesn’t matter at all.

> Are TIFF, BMP, and PCX really considered to be forgotten?

Yes, we are that old.

Pretty much all the .bmp files on my computer are ones I've carried over from my Windows 95 days.

Quake screenshots used to be some weirdo format that started with a T (TIFF? Targa?) and I had to use some program that wasn't Paint to open them. Now that people use customized GPLed versions of the game, I think all of them output something common like PNG.

.pcx I only dimly remember.

Kevin Schumacher

@Sören After further testing I have determined that it always sends JPGs when you use the "quick" functionality--that is, take a screenshot and tap on the small preview that appears in the lower left of your screen, then AirDrop it from there. If you take a screenshot and let it be saved to your Photos library, then use AirDrop in there, it always sends PNGs. This is true even if you send the same screenshot twice - once from the preview, and then save it to Photos and send it again from there.

The names differ, too. Screenshots sent from the Photos library use IMG_####.PNG (PNG in uppercase), which has been the standard in that library for the entire time iPhone has been around, to my knowledge.

Screenshots sent from the preview immediately after taking them have a format of IMG_@@@@@@@@@@@@-1.jpeg (jpeg in lowercase), where @ is a random uppercase letter or number. If you take multiple screenshots in quick succession and tap the preview then use Share, it will send all of the screenshots you just took. They will have different random 12-character strings in the middle of the name, but the number after the second dash will increment for each additional file (so two screenshots will be IMG_ABCDEFGHIJKL-1.jpeg and IMG_ZYX123098TRS-2.jpeg).

I have Settings > Photos > Transfer to Mac or PC set to Automatic, and Settings > Camera > Formats set to Most Compatible. I did try adjusting both of those settings to the opposite values (Transfer set to Keep Originals, and Formats set to High Efficiency) but it made no difference.

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