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Bayer Interpolation
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Bayer Interpolation

A pixel is defined as a complete set of color data for a point in an image. Some pixels may be colored red and others may be colored green, but there are no such things as red pixels or green pixels. A pixel is a complete pixel only when the red, green and blue values are known for the unique location of that pixel.

Digital camera makers all lie about megapixels. This is OK today, because unlike other specs, all legitimate camera makers lie in exactly the same way. This means it's easy to compare cameras from different makers.

Digital Cameras

Digital camera pixels aren't as sharp as scanned film pixels.

All digital cameras, except for $30,000 scanning backs and the old Sigmas, have only a third of their claimed pixels! Instead of having separate R, G and B sensors for each pixel location, they only have a single monochrome CCD with each pixel location painted with a R, G or B filter. This alternating R, G and B filter matrix most often follows the Bayer pattern with twice as many G as R or B spots. This is named for Kodak scientist Bryce Bayer who invented this in 1976.

A special Bayer interpolation algorithm is then used to create separate R, G and B values for every pixel location. Remember that before this interpolation that each location only had a R or G or B value; not a R value and a G value and a B value for each location.

The algorithm creates values for each of the three colors at every location by smearing (interpolating) each set of partial R, G and B values to create values at every location.

These algorithms are proprietary to each camera maker. They become more clever with time to allow higher perceived sharpness more closely simulating full resolution. As of 2006 these clever algorithms allow starting with one-third the data and making it look about as good as having one-half the number of pixels claimed.

Raw and JPG

These all start from the same data. The sensor is unchanged regardless of the mode you select in-camera.

RAW offers no advantages here, except for one potential gamble. Bayer interpolation takes place in the software opening the raw data. Future advances in Bayer interpolation algorithms could be incorporated in future raw software, if and only if your camera maker continues to support yesterday's cameras in tomorrow's software. Just as likely, your camera maker may no longer support your old camera in tomorrow's raw software!

I shoot JPG.

Scanned Film

Scanned film and images reduced to fit the web have full red, green and blue resolution for every pixel. They look as sharp at 100% as they do reduced.

Scanners do this because they have three separate sets of CCDs, one for each color.

Therefore, a scanned image can be sharper than a digital camera image of the same resolution. Of course to do this the scanner's optics and the image on the film being scanned must be sharp enough to support it.

EXAMPLE

Roll your mouse over to see image without Bayer interpolation.

The original image is cropped from a Nikon D200 at 100%. Like every other digital camera, it is Bayer-interpolated. Roll your mouse over it to see the same image, at full RGB resolution without the interpolation. If still cameras used three CCDs like professional video cameras we wouldn't need Bayer Interpolation.

The full resolution image was also shot on my D200, but with a lens of twice the focal length. I then downsampled it to half the size. By resizing the image to half the linear pixel dimensions, Photoshop takes four pixels and combines them into one. This has enough information to get full RGB resolution for this example.

The base image was shot with a Zeiss ZF 50mm lens at f/5.6. The other image was shot with a 105mm Micro lens at f/5.6. Obviously the light and wind changed from shot to shot. The tripod wasn't moved. Each lens has more resolution than my D200 at these apertures.

Of course you could apply sharpening. That would make it sharper, but not increase the resolution. Here's the Bayer-interpolated image with added sharpening (150% at 0.3 pixels). Compare it to the non-interpolated image.

bayer resampling

Ritz Camera

adorama

I personally buy from Ritz, Adorama and Amazon. I can't vouch for any other ads.

 

 

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