We were having a discussion over Christmeas about the relative detail that current digital cameras can achieve vis. a vis. chromgenic B&W. The best digital camera I have seen offers 2 million pixels per frame. How many equivalnet "dots" or "grains" does a chomogenic film have in the same area ? Can anyone help ? How does this compare with say FP5 ? The digital enthusiast said that electronic cameras were now approaching the same definition as normal film. I said I thought he was way out in his calculations - but maybe I'm wrong. What are the facts ?

-- Anthony Brookes (gdz00@lineone.net), December 29, 1999

Answers

I went to a seminar about 6 months ago that was directly aimed at the professional market (ie. I was invited by a friend and went along as a "hanger on". Anyway, your query was was one of the main features in one of the presentations. I can't find my notes at present, but I recall that they claimed a 35mm neg has about 18 to 25 million "grains"; a 6x6 neg, somewhere in the area of 128 to 170 million! As a rough rule of thumb, 1 pixel=1 grain. If I find my notes, I'll post more precise figures. In any event, it seems that megapixel cameras still have a bit of catching up to do. Whether the human eye can distinguish.... well, that's another question for another time...

-- Frank Alvaro (falvaro@ozemail.com.au), December 29, 1999.

There are a number of possible measurements.

One is grain size. I wrote up an experiment on Delta 3200 in photo.net, but I can't find the post, and don't seem to have kept a copy.

Another is how much detail can be digitally scrapped from the negative. A figure of 4000 dpi is often quoted, and this is 157 dots per mm. For a 24x36mm negative, this is 21 million dots.

Another is how much detail is recorded by the lens/film combination. This could be 50 lp/mm (line PAIRS per mm), or 100 dots per mm. For a 24x36mm neg, this is 8 million dots.

-- Alan Gibson (Alan.Gibson@technologist.com), December 31, 1999.

One thing to watch with digital, is that many cameras count EACH color site as a pixel, and it takes three color sites (Red, Green, Blue) to display the picture element in full color.

So in digital pixels, you need to divide the number of pixels by 3 to get the actual number of information "spots".

This is sort of like counting the number of grains in each of the three color layers of a piece of color film, and reporting that as "pixels."

-- Terry Carrway (TCarraway@compuserve.com), December 31, 1999.

Many thanks for all your answers. It seems that digital has along way to go to get anywhere near silver film, and even further for chromogenic film.

-- Anthony Brookes (gdz00@lineone.net), January 02, 2000.