Yesterday I tried to downscale a 43520x47872 image with GraphicsMagick. The command line I used was gm convert -limit pixels 2500MP -filter box -resize 50% DokshitsiCut.tif C:\DokshitsiCut.png.
I expected the conversion to take about an hour at most, but after six hours I was still faced with heavy HDD activity and no end in sight. By that time my patience was entirely spent, so I decided to call it quits, but not before determining what GraphicsMagick was doing, so that I could report it here. Turned out the program created three files in the temporary directory: gm3Vya4M of about 8 GB, gmIgdh9H of about 4 GB and gmURFlG6 of about 2 GB. A look at the Process Monitor revealed that it was writing data to gmURFlG6 by chunks and each chunk had the size of four bytes. That's right, FOUR BYTES.
I, of course, don't know for sure what planet the programmer who wrote the routine does live on, but with the technology we currently have on Earth such operations would probably take days even on an SSD, and on HDD... well, let's say they would take MANY days. No wonder that after so many hours the file mostly consisted of binary zeroes. In comparison, Adobe Photoshop CS5.1 completed the same task in about 17 minutes.
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