12MP resized to 8MP ?

Started Sep 3, 2008 | Discussions thread
Dave Ingols
Regular MemberPosts: 258
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Bicubic vs. Lanczos-8
In reply to Mike86, Sep 5, 2008

While the other replies contain some validity, they are all forgetting some important issues.

1. The resampling when downsizing in the camera is most likely occurring from the RAW sensor data, so the usual assumptions about how RGB data is interpolated for down-sampling cannot be applied with a high degree of certainty.

2. In-Camera resizing is probably using some form of Bicubic algorithm. As with all in-camera processing they try to use the simplest/fastest method. This is why de-noising on your computer works so much better. You can run more elaborate de-noise methods on the data than your camera can.

3. A camera doesn't have the processing-power nor the time needed to use the best resampling algorithm, Lanczos-8. If you downsize an image in Photoshop for example, that program only allows you to use the Bicubic method. This is due to Photoshop only being a 16-bit floating-point math platform, yes, even CS3. They've never changed that in all these years. They can't include processes that require more math precision. Photoshop's only best option of Bicubic results in loss of fine details, soft edges, and a general smearing of data at the pixel level. Other more powerful 32-bit-math programs that were designed in this century include some form of the Lanczos algorithm for resampling. Lanczos, Lanczos-3, Lanczos-8 of one form or another is found in most 32-bit applications these days. Even freeware Irfanview includes standard Lanczos as a resampling option for resizing. I usually use the inclusion of Lanczos in the software as my benchmark on the quality of any program. The better the Lanczos algorithm included, the better the program. I only use editors that include Lanczos-8 now. When resizing or doing rotations in small to large degrees Lanczos assures you the smallest loss of details in your images.

4. Taking this information into account, you could probably do better downsizing your images in your computer if you use better resampling algorithms than what is available in your camera or in antiquated 16-bit software.

See this page for a nice overview of interpolation methods and the test results. http://home.no.net/dmaurer/~dersch/interpolator/interpolator.html

"Sinc 256" on that page is the same as Lanczos-8

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