PixelZap takes the fight to hot pixels! (UPDATED)
By
Mike Tomkins
(Wednesday, July 25, 2001 - 02:19 EDT)
New software from TawbaWare removes hot and stuck pixels from images with minimal damage...
Digital camera users whose cameras offer long exposure modes without noise removal algorithms will doubtless be familiar with the effects of dark current noise, the effect that causes a seemingly random noise pattern of 'hot' pixels to appear on long exposure images. The patterns actually aren't random, and relate to sensor temperature and the length of the exposure - but correction techniques that exploit this fact can be somewhat clumsy depending on what software you're using.
Another similar problem is that of the stuck pixel - always remaining the same color regardless of the subject, this is something that can strike pretty much any digital camera at some stage, and whilst usually not noticeable, is bound to annoy once you do notice the defect - by which time it may be in hundreds of images! Similarly to dark current noise, techniques exist to fix this problem, with varying degrees of sophistication currently.
A new program from Max Lyons, author of the popular Thumber and a range of other imaging utilities, has now released his own stand-alone program for removing both types of noise from your digital images. Available in both DOS command-line and Windows GUI versions, PixelZap promises to intelligently remove dark current noise, and to correct pixels the user defines as stuck - and to do so with minimal damage to the JPEG file from recompression, which can introduce artifacts and degrade image quality.
Max describes the program much more eloquently than we could: "PixelZap is designed to remove 'hot pixels' from digital camera images caused by 'noisy' long-exposures and/or a defective or aging CCD. When correcting hot pixels caused by long exposures, PixelZap is able to automatically detect, and correct hot pixels. When correcting hot pixels caused by a defective or aging CCD, PixelZap only corrects those pixels that are specified by the user.
One of PixelZap's most important features is its ability to save JPEG images in a 'virtually lossless' fashion. PixelZap uses low-level JPEG compression/decompression techniques to resave a JPEG image with essentially no image quality degradation. (More details in PZapGUI's help file). This is particularly useful when correcting images with hot pixels due to a defective CCD -- only the specified pixels are changed, and the rest are left untouched.
PixelZap also includes a number of features designed specifically to work with the types of images created by current digital cameras. For example, it is able to retain EXIF data in the corrected image, and its default detection and correction algorithms search for hot pixels in 2x2 clusters. This 2x2 clustering occurs because of the way color information is recorded by digital cameras, and allows PixelZap to accurately detect problem pixels, and lowers the chance of PixelZap falsely detecting bright points in the image that are not caused by hot-pixels.
PixelZap is a command-line (DOS) program designed to be as small (approx. 130KB) and fast as possible. I have also released a Windows program (PZapGUI) for users who prefer a graphical version of the software. PZapGUI allows the user to process batches of images, and easily compare "before" and "after" pictures. PixelZap and PZapGUI are released as shareware, but will operate for an unlimited time without registration. However, the unregistered versions are limited to processing images no larger than 640x480.
PixelZap and PZapGUI can be downloaded here." We tested Max's program on a sample image from our review of Olympus' Camedia C-3030Zoom digital camera, and the results were pretty impressive - even with default settings! The images are a bit large to include in the news page, so you can instead see 500 x 740 pixel crops of the color chart by clicking on the links below, which will open in a new window... For more information and to download PixelZap or PZapGUI, visit the TawbaWare website. The program can be registered allowing unlimited image sizes for a cost of $15, and a site license is available for $80.
UPDATED 2001-07-26 16:35ET: As we mentioned in the news item above, there are existing alternatives for removing dark current noise from digital images. IR reader 'Ulysses' wrote in to point out a couple of these alternatives, in the form of two programs we mentioned on this page last year from MediaChance. HotPixels Eliminator attempts to remove noise and 'blue chunks' from long exposure images by making calculated guesses as to what is part of the scene, and what isn't. BlackFrame NR meanwhile requires that you capture a dark current frame (essentially, a second photo immediately before or after your 'real' photo, with exactly the same camera settings but with the lens cap on the camera. The dark current frame is subtracted from the real photo, and the resulting 'holes' in the image where previously there were hot pixels are filled in using surrounding image data. Thanks for the email, 'Ulysses'!
Source:
TawbaWare website
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