[Ray Pulley]

I always understood that because the human eye is most sensitive to green light you want the measurement across an image to be the most accurate in that wavelength. So in the interpolation algorithm the Bayer filter provides double the information in green levels.

The sensor Bayer CFA (color filter array) is not RGB, it is actually RGGB. There are 2 greens for every red and blue. This is to more closely mimic the human visual system.

From Wikipedia:

"Bryce Bayer's patent (U.S. Patent No. 3,971,065) in 1976 called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements. He used twice as many green elements as red or blue to mimic the physiology of the human eye. The luminance perception of the human retina uses M and L cone cells combined, during daylight vision, which are most sensitive to green light. These elements are referred to as sensor elements, sensels, pixel sensors, or simply pixels; sample values sensed by them, after interpolation, become image pixels."

Ray

[longview]

Blowing channels is something that affects pretty much all digital sensors and some films even, the only permanent solution is to use something like the Foveon sensor in the Sigma SD-1. Videographers have long understood the problem with 4:2:2 video (although it's still common for pro-use for the same reason as in photography -- it's way cheaper) reducing colour resolution.

Underexposing half a stop or so, or watching the RGB histograms when shooting is also a way around it, with the K-5 it shouldn't be a problem to push the image in post, but you still need to watch your processing carefully when dealing with critical colours.

[SteveB]

I don't have a K-5 but I think this red problem is common to most digital cameras. Underexposing and using RAW is the only way to get accurate reds on my K100D. If using JPGs, underexposing will help, as will cutting saturation and contrast and using Natural rather than Bright mode but you'll never get near the results possible with RAW. By the way, you can see the problem quite easily in the 2 images in "The great K-5 RAW vs JPG debate" thread.

[Rupert]

For whatever reasons, my K10D seemed to do reds better by far than my K5. If you are not very careful you will blow the reds with the K5 almost every time. Raw helps, but will not eliminate the problem in the majority of cases where I have blown reds. Other colors are fairly easily corrected, but red refuses to cooperate, even in Raw far too often.

I do agree,it is not just Pentax, I see it in almost every brand to some extent. I would like to see some Sigma examples....maybe they are better?

Regards!