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ImagingIn a test at Luminous-Landscape "30D vs Film" the 8.2 MP Canon 30D produced better results.
They used a $10,000 Imacon FlexTight Photo to scan a Fuji Provia 100F film image, arguably the finest grained, sharpest ISO 100 speed film available, at 3200 DPI.
Professional slide film has a grain size of between 8 and 11 microns (Fuji Velvia 100F has an RMS grain size of 9 microns)
Something called Nyquist's Theorem states that you would need to scan at at least twice the resolution to get the information in the original. That works out to about 5600 dpi and scanning at this would yield a file with over 40 megapixels. And it gets worse than that potentially for scanning film since grain is both irregularly sized and irregularly spaced.
Color print film A typical colour negative film (such as consumer 35 mm film) has silver-halide crystals to sense the light. These are (depending on the speed of the film - faster = bigger), in the range of 0.5 to 3 microns in diameter.
The term "film grain" is often incorrectly used to describe the "fundamental" particles in a
chemical-based photographic image. Fundamental image particles are the smallest particles that form an image: (a) silver particles (0.2- 2.0 um) or (b) color dye clouds (10- 15 um), while grain is 10-30 um.
Prints are formed of tiny dye-clouds, centred on the position of a silver-halide crystal that was exposed and developed. These dye clouds are formed from many very tiny (sub-micron) oil droplets which were coated with the silver halide, and each contains a chemical which reacts with oxidised developer to form dye. Dye clouds vary in size and can be generated from a number of silver halide crystals, depending on how much exposure there was in an area; they can overlap with each other, and of course the packing density of the silver-halide grains themselves has an impact on the granularity.
Transparency films are said to be grainless because there are no silver particles in the final emulsion, and the dye clouds have indistinct edges. While silver particle are present in color film before, and during, the many stages of the development process. At a point, the silver particles are bleached out.
ScanTips.com says "When we get right down to it, scanning color prints can rarely yield more detail when scanned at more than 300 dpi. I am carefully saying color prints, to exclude film and B&W prints.
A digital camera records only red, green or blue at each photosite in a Bayer mosaic pattern and interpolates the remaining values to the true resolution possible is dependent on the quality of the interpolation algorithm used. Each photosite can typically register 256 levels (8-bit) of luminance. A 10.1 MP Cannon EOS XTi produces about a 10-12 MB RAW12 file.
The human eye can resolve at best about 1 minute of arc, 1/3440 (Blackwell, 1946). You can see things smaller than this, but you can't distinguish between two objects closer together than this. 300mm (12")/3400 yields 87 microns ; 300 dpi is 84 microns per dot. 2 dots are required for one period if we want to speak in terms of line pairs. Young human eyes may be able to resolve 60 microns.
It can distinguish about 100 levels of brightness
and very early in our neural pathway, connecting eye to brain, we split
the signals into colour and brightness (or in jargon - chrominance and
luminance). We have three chrominance receptors, roughly sensitive to
blue, red and green light. Our sense of luminance is derived about 60%
from our green receptors, 30% from the red and only 10% from the blue. We
can see luminance detail about 0.2mm wide in an image about 350mm or 14
inches away (normal viewing distance). We cannot see small details in
Because poster size prints (larger than 8x10) are generally viewed from an arm's length or farther, less pixels per inch (ppi) are required to produce a quality image. For good quality posters, 150 ppi is recommended.
# 200 ppi - Good to Very Good Recommended
Nikon D80 SLR 23.7 x 15.7 mm = 2x3 Nikon Coolpix 8800 8.8 x 6.6 mm = 3x4 Olympus E (four thirds) 13.0 x1 7.3 mm = 3x4300 ppi.
A photo printer needs at least 600 x 600 dpi.
Some offer up to 4800 x 1200 dpi color prints.
6 ink printers up to 73 Million colors.
Is this more hype to sell new printers, since the human eye can only detect 300 dpi at 12"? I guess if you want to look at your pictures thru a magnifying glass it might be necessary. I've got to look into the basis for this statement.
Printer detail and ppi at Clarkvision
Grain size in Photographic Film
Digital Camera Resolution versus Film Scanner Resolution - Photo Tips @ Earthbound Light
30D vs Film
Digital Resolution at modernviews.com
Human Vision and Digital Imaging
A comparison between the use of a high-resolution CCD camera and 35 mm film for obtaining colured micrographs from www.blackwell-synergy.com/doi/
Film Grain, Resolution and Fundamental Film Particles
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