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A Building Made of Sky

Comments: 12

Couldn’t get back in the saddle here without posting a photograph. This is a building made of sky that I saw today.

Notice how the JPEG algorithm runs nasty little comression stripes down around the margins of the picture? It’s most noticeable on verticals down the sides. Graphic Converter was doing it, too, so I guess it’s the JPEG procedure rather than a particular app.

The 24-bit PNG looks great — but weighs in almost 5 times heavier. I hope compression algorithm optimisation converges on increased bandwidth for all in a happy medium of online photographic lushness real soon.

By the way, click that image for a larger version (in a new window) where the horrible compressions stripes are plainly visible.

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Posted to Photographs • 2003.12.04 (Thu) • 23:22

Comments

Posted by Pascale Soleil 2003.12.05, 02:49

Perhaps I’m blind as a bat, but I swear I see NO stripes. And I’m pretty fussy about images.

Posted by Pascale Soleil 2003.12.05, 02:50

Just a thought… do you have your monitor set to True Color (millions)?

Posted by resonance 2003.12.05, 03:09

The stripes are there. Due to the way the JPG compression algorithm works, it’s not uncommon to see these artifacts at the edges of large blocks of color (particularly ones with subtle gradients such as the sky in this photo). You can also see the artifacts forming a slight, light ‘halo’ a few pixels around the buildings, particularly the one to the right.

My monitor is hardware-calibrated and always runs at 24-bit color. The lines are residue from the algorithm.

Posted by Adam Rice 2003.12.05, 04:49

Graphic Converter does have two different JPEG algorithms—I wonder if whichever one we’re not seeing here would produce better results. And of course, if you trade compression for quality, the artifacts should be minimal.

I can see some jaggies in the sloping roof of the mirrored building, but for a JPEG, I think this image looks pretty good.

Posted by Jeff Lawson 2003.12.05, 06:29

Could the black 1px borders be screwing with the algorithm as well? I know I’ve gotten some weird compression artifacts from borders before.

Awhile back, I decided to just stick with uncompressed JPEGs when posting photos on my weblog. Granted, the full-size versions end up somewhere in the 200-300K range (more if there’s a lot of detail), and the smaller inline versions end up being 50-100K, but I have bandwidth to spare. Plus, I expect most of my visitors are broadband users and won’t notice the extra half a second it takes to download the file. I think the higher image quality is more than worth the extra bytes.

Posted by jon 2003.12.05, 06:49

It’s like an invisible building. Fantastic!

Posted by Tim Conner 2003.12.05, 07:39

It’s often the case with the jpg compression algorithm that horizontal or vertical lines in will become jagged or broken. This is very common on houses where the horizontal lines of the siding is repeated. A minimal rotate of a fraction of a degree will usually fix the problem. Or, sale that image at a percent that isn’t in thirds. Scaling image to 33 or 66 percent will produce the most ‘jaggedness’ scaling to 38 percent will produce less ‘jaggys’. Just a few tips that I’ve found - they are not however silver bullets.

Posted by Morgan Roderick 2003.12.05, 08:24

When doing png for web use, sometimes it is useful to give them a run through PNG Crush

http://pmt.sourceforge.net/pngcrush/

available for most OS’es http://www.google.com/search?hl=&cat=&meta=&q=png+crush

Posted by jh 2003.12.05, 10:28

Thanks for the advice, everyone.

Yes, monitor is at 24-bit. The stripes were present in Photoshop whether I used the save-for-web routine or the regular save-as JPEG method (to be expected as I doubt PS would be using a different compression routine for the two methods). It was also present in Graphic Converter no matter which of its JPEG methods I used.

In all instances the stripes appear whether or not the border is present.

Posted by frank 2003.12.05, 21:35