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Scaling Algorithm Bug In Gimp, Photoshop, Others
Wescotte writes "There is an important error in most photography scaling algorithms. All software tested has the problem: The Gimp, Adobe Photoshop, CinePaint, Nip2, ImageMagick, GQview, Eye of Gnome, Paint, and Krita. The problem exists across three different operating systems: Linux, Mac OS X, and Windows. (These exceptions have subsequently been reported — this software does not suffer from the problem: the Netpbm toolkit for graphic manipulations, the developing GEGL toolkit, 32-bit encoded images in Photoshop CS3, the latest version of Image Analyzer, the image exporters in Aperture 1.5.6, the latest version of Rendera, Adobe Lightroom 1.4.1, Pixelmator for Mac OS X, Paint Shop Pro X2, and the Preview app in Mac OS X starting from version 10.6.) Photographs scaled with the affected software are degraded, because of incorrect algorithmic accounting for monitor gamma. The degradation is often faint, but probably most pictures contain at least an array where the degradation is clearly visible. I believe this has happened since the first versions of these programs, maybe 20 years ago."
My software has been calculating in linear space for over a decade now (this is the Nuke Compositor currenlty produced by The Foundry but at the time it was used by Digital Domain for Titanic). You can see some pages I wrote on the effect here: http://mysite.verizon.net/~spitzak/conversion/composite.html. See here for the overall paper: http://mysite.verizon.net/~spitzak/conversion/index.html and a Siggraph paper on the conversion of such images here: http://mysite.verizon.net/~spitzak/conversion/sketches_0265.pdf, in fact a lot more work went into figuring out how to get such linear images to show on the screen on hardware of that era than on the obvious need to do the math in linear. Initial work on this was done for Apollo 13 as the problems with gamma were quite obvious when scaling images of small bright objects against the black of space.
For typical photographs the effect is not very visible in scaling, as the gamma curve is very close to a straight line for two close points and thus the result is not very much different. Only widely separated points (ie very high contrast images with sharp edges) will show a visible difference. This probably means you are trying to scale line art, there are screenshots in the html pages showing the results of this. Far worse errors can be found in lighting calculations and in filtering operations such as blur. At the time even the most expensive professional 3D renderers were doing lighting completely wrong, but things have gotten better now that they can use floating point intermediate images.
One big annoyance is that you better do the math in floating point. Even 16 bits is insufficient for linear light levels as the black points will be too far apart and visible (the space is wasted on many many more white levels than you ever would need). A logarithmic system is needed, and on modern hardware you might as well use IEEE floating point, or the ILM "half" standard for 16-bit floating point.
1. Spend a lot of time calibrating your camera yourself. This is only cheap if your time is worthless
Typically this should be done during the initial set-up of any new camera that a photographer purchases. A Gretag Macbeth colour checker is cheap, the required shot to evaluate the performance of the sensor is quick and easy to set-up and the processing of this test image is fast with the right tools (like this script for photoshop). It should take under an hour to do it right and get it as part of the automatic stage of processing your RAW files (basically setting ACR/Lightroom's demosaicing stage), but the benefit is that every picture taken from then onwards does not need extra calibration. Thus your prints look like your shots, assuming the rest of your workflow is equally as calibrated.
While your time is valuable, if you do not calibrate like this, you're wasting time further down the line for EACH image, and thus it's more expensive to not do it...