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Author Topic: A Most EXCELLENT treatment for Hot Pixels  (Read 2730 times)
Lin Evans
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« on: January 19, 2006, 11:29:42 PM »
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I had a cluster of about five dead (hot) pixels on my R1 and Sony's technical service was less than helpful, at least for my needs.

Virtually all sensors have dead pixels and firmware has mapping algorithms which substitute adjacent good pixel values for those missing from these regions. Sometimes - actually more often than not - a cluster or so of hot pixels slip by and are not mapped. Some companies such as Olympus provide the user with mapping software and user upgradeable firmware correction to keep the sensor's output pristine in appearance. As a sensor ages, more "hot" pixels will begin to appear. It's quite easy to see hot pixels when taking night exposures and the number increases with exposure time and subsequent "heat". Many manufacturers have what is called "dark frame" subtraction where your exposure is compared with a hot pixel mapped dark frame and any hot pixels are "removed" from the exposure. This effectively doubles the time necessary to wait for your image. For example if you take a 3 minute exposure at a given aperture then a corresponding "dark frame" is taken immediately afterward by the firmware. This value is then used to remove the offending noise and hot pixels but the trade-off is that you must wait double the exposure time or "six" minutes to get your results.

Sony told me that they have no user software to fix hot pixel issues and that I should send my R1 to them for "evaluation" to see if it is or is not within tolerance. That's unacceptable to me for fixing a cluster of about five visible pixels which show up as a rather small red dot. It would mean being without my new toy for an extended period and absolutely zero assurance that anything would be done about it anyway so I elected to forget that "solution" and look for alternatives. Of course it's simple enough to clone out these offending dead pixels using PhotoShop, but that's also annoying to have to do for every image where they are conspicuous. So I set out on a quest to find a software solution.

I found an excellent software program written by Max Lyons. For those unfamiliar with Max, he created the first gigapixel image with a digital camera when he stitched 196 separate six megapixel captures of Bryce Canyon and created a 1.09 gigapixel file of over 2 gigabytes in size. He displayed a 300dpi uninterpolated LightJet print of 8x12 feet at PMA in Las Vegas a couple years ago which was absolutely stunning! Max also writes an excellent GUI front end for PanoTools to facilitate making stitched panoramas, but I wasn't aware of his very nice pixel zapping software. I downloaded the trial shareware version (it only works for 640x480 or smaller images) and tried it with superb results. I then bought the software ($15 U.S.D.) and within 15 minutes of downloading the trial had a full working version which does a beautiful job. The software is VERY flexible and you get two flavors. It only works on jpg files but saves them in a lossless fashion so is still very useful. It can also output BMP format, but the jpg's are virtually indistinguishable from the originals except the offending hot pixels are gone...... If you download it, be sure to also download the help file for the GuI version. You get two versions for the price of one. There is a script enabled command line version and the GUI version. Each can handle single or folder containing multiple images to process.

Here's a link for anyone interested:

http://www.tawbaware.com/pixelzap.htm


Best regards,


Lin
« Last Edit: January 19, 2006, 11:30:30 PM by Lin Evans » Logged

Lin
Ray
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« Reply #1 on: January 22, 2006, 05:49:07 AM »
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Lin,
Pixmantec's RawShooter includes a very effective 'hot pixel/pattern noise suppression' tool, which of course works on the RAW file. Adobe's ACR seems to include a default 'hot pixel' removal facility which is not user adjustable, but which works behind the scenes. I'm assuming this is the case because with RSP's hot pixel remover turned down, when converting a high ISO image, there are lots of hot pixels visible which aren't visible in ACR.
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