About Bob Todrick Expertise I can answer questions on most areas of photography. Though fine-art nudes is my main focus, I can, as well answer most questions dealing with darkroom processes (including many alternative processes).
My expertise does not include digital.
Experience I have photographed since 1975. Among my clients have been a number of major retail department stores (the Bay, Eatons). I photographed for Canada's premier motorsports magazine for a number of years, and have done much portraiture and wedding photography.
In 1990 I gave up shooting professionally to concentrate on my fine-art work and have had numerous group and one person shows since.
Organizations Co-founder of the Group of Several.
Publications Numerous newspaper and print ads.
GRAPHIS photo annual.
Expert: Bob Todrick Date: 8/14/2004 Subject: digital camera CCD's and other chips
Question Bob,
I am a photographer who has not yet purchased a digital camera, but who does scan slides for producing prints via Photoshop.
What I can't get my head round, is where the digital file originates vis-a-vis the chip in a digital camera.
I have read the excellent "Advanced Photography" by Michael Langford, and he explains that a CCD has an array of photosites sensitive to either red, green or blue in the ratio 1:2:1. Does this therefore mean that a 4 megapixel CCD contains 1 million red, 2 million green and 1 million blue photosites; and that the 4 megapixel file is obtained by interpolation using a mathematical averaging method.
If this is so, then the accuracy of the image owes as much to the algorithm used as it does to the quality of the colour filters and the chip.
You have only to see how the differences between the various compression files result in strange edge effects and random colour patches.
Scanning a slide with my £300 bottom of the range scanner gives me a huge file (something like 11 megabytes), which sounds great, until you begin to wonder whether the scanner software plays around with the data or not. The image seems real enough, even under maximum magnification....
Anyway, sorry about rambling on, but the question is .... is a 4 megabyte CCD really giving 4 million true and independent sets of readings on the three colour channels?
John
Answer You ask some interesting questions that may be better answered by someone with more of a technical knowledge base than I...but here goes.
You are correct about the way the megapixels are broken up, color wise. Research has been done (the Fovean chip) wherein each pixel site measures blue, green and red. Supposedly this would give a much better image, but no one (Fovean and Sigma) seem to be able to make it work.
You are also correct about the algorithm being responsible for much of the image. In a conventional camera two different brands, with comparable lenses and using the same film, will give pretty much identical images.
Not so with digital cameras. Firmware, software and a number of other factors come into play before the image is produced. In reality all the 'megapixel' tells you is how big an image the camera will give...not the quality.
For example take two 6 megapixel cameras...a digital SLR with a sensor nearly the size of a 35mm frame of film and a digital point and shoot with a sensor the size of you little fingernail.
Both 6 megapixels.
Both will give approximately the same size image on raw.
But each of the 6 million sensor sites of the SLR is 4X the size of the point and shoot cameras.
Bigger sensor...more sensitive in low light.
Bigger sensor...better control of high contrast scenes.
Bigger sensor...less noise when higher ISO's are used.
Bigger sensor...same size image but much better quality.
And by the way...your 300 pd scanner, will give better results than all but the high end digital SLR's. Don't let anyone tell you different...film (even scanned) wins hands down in the quality race over digital. A 35mm frame of a good quality slide film such as Fuji Provia 100 has about 25 'magabytes' of information on it...and a good quality scanner picks up much of this extra info.
Hope this helps.
