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In the prior thread, Wolfus asked if “lossy” was a Britishism. It ain’t. And because I’m desperate for stuff to post about at the moment, I shall explain what it is.

“Generation loss” is a thing in graphic arts. It means that every time you make a copy of something — every time it goes down a generation — it loses quality. If you have an illustration, and you photograph it, and then you do a color separation, and then you print it in a magazine…every stage of that process involves a degradation of the original.

Then if you make a photocopy of the magazine article and digitize it to put in your slide presentation…don’t laugh. I often deal with images that are many generations removed from the original.

That’s generation loss; the term “lossy” is used specifically for digital file formats.

The Targa tiff file — which you may never have run across — was a common early digital file format that purported to be lossless. In theory, you could make a tif file of a tif file and every one was as good as the original. Downside: they were huge.

Lots of file formats have used all sorts of clever algorithms to try to squeeze file size without losing quality.

The jpg file came to rule them all because it’s very, very good at the trade off…it can look very good, or it can compress very small, or it can be a compromise, depending on what you ask it to do. That’s what it’s asking when a graphics program gives you a jpg quality slider.

The image at right is a jpg compressed at a quality of about 70% (100% means very little loss, very little compression) and it’s about 36K on the disk. The inset is compressed at around 10% (lots of loss, lots of compression) and is about 7K.

Notice the characteristic big square blocks that are the hallmark of jpg compression. I bet you’ve seen that before! Different lossy formats are ugly in different ways and when I get my Photoshop back, I can show you.

That’s not my big white rooster, by the way. That’s my old lavender hen Violence (may she rest in peace). I’ve had three lavender chickens, and they’ve all hated me.

November 28, 2018 — 9:32 pm
Comments: 7