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Film vs Digital Imaging
Digital - Part I - Digital Stills The introduction of digital still photography is still in the "Wild West" era. The rules are being made up as we go along. There are emerging professional standards but as usual they require significant knowledge and investment to use to your advantage (colour management being one of the more significant).The huge advantage that digital imaging has is that it allows for instant non-destructive manipulation (read Photoshop).
The current craze is being marketed on the ideas of no cost shooting and editing and low cost home printing. The no cost shooting and editing aspect is of most significance to commercial photographers who retain very few of the huge number of "product" images they produce and they seldom if ever need prints. The digital production cycle goes right through to the printing press with huge benefits for this portion of the industry.
The appeal of instant verification of your shot and the ability to discard the ones where the wag has given the groom a pair of horns is undeniable but the issue is far more complex than that ... it's the little things that make capturing the ideal image a combination of anticipation and good reflexes. So issues like the time between when you push the button and the time when the image is recorded is the difference between what you saw and wanted and the group breaking up and waking away.
CCD vs CMOS
The differences between CCD and CMOS sensors is largely an issue for engineers as far as I can determine. CMOS is cheaper but initially produced more "noise" in the image ... I think that issue has been resolved. So I can't really argue one device over the other.
The image sensor is a solid state chip that has a grid of very small light sensitive devices that are the picture elements or pixels of your digital camera. These chips range in size from smaller than your little finger nail right on up to as big as Uncle Sam can afford. The 14 megapixel chip in the Kodak professional SLR cameras is 24 X 36 mm (the same size as a frame of 35mm film) ... which is convenient because then the lenses made for film cameras give the same performance on the digital cameras. On digital SLR's that have smaller sensors but are still capable of taking the lenses from a film system they usually tell you that there is a magnification factor of say 1.6. This number means that the image will look like it was taken with a lens 1.6 times as long. Said another way: if you used a 50mm lens on the digital camera it would give you the same angle of view as it would if you used an 80mm lens on the 35mm camera.
The electrical signals of the sensors are read in different ways but what is important is that the output is a digital number which represents the brightness of that pixel. The larger the digital number (or bit depth) collected from each pixel the larger the range of brightnesses that can be represented from each pixel (up to the point where changes in bit depth can no longer be discerned by the human eye).
So now you have information about the relative brightness of millions of points on the area of the camera sensor that if you translate back into points of white paper and black ink you see a representation of the black and white image captured digitally.
The computer in the camera that reads the values of the pixels and records them to memory has two other vital functions. Thus far we have only got image density information. To get colour from a single chip camera there has been a Red/Green/Blue (RGB) filter matrix laid over the image sensors (more green then red or blue for some reason). The computer must mathematically calculate from the differences in density caused by the filters what colours to attribute to each pixel (and miracle of miracles it does a creditable, if not perfect job). And then the computer must process the image file and usually compress the size of the image file to be saved as a JPEG file.
| 1 MP | images suitable for online use only |
|---|---|
| 2 MP | images suitable for online use only |
| 3 MP | images suitable for online use and very small prints |
| 4 MP | good for 4x6 prints |
| 5 MP | approaching usable resolution |
| 6 MP | considered to be sort of 35mm equivalent |
| 14 MP | full 24 X 36mm digital sensor |
N.B. 2 - All digital still cameras that have single chip sensors mathematically interpolate colour ... except those which have a Foveon chip. The only cameras that have the Foveon chip are industrial cameras from Foveon, two models of SLR from Sigma and perhaps by now a point and shoot from HP.
N.B. 3 - 35mm film can be scanned using medium priced scanners to produce 24 megapixel full colour images. This can be improved upon using high end scanners.
N.B. 4 - Digital images from the medium to higher ranges can be successfully manipulated in the computer to enhance their resolution by interpolation (or other mathematical manipulation) and multiple images can be seamlessly joined to produce very high resolution images.
Posted October 4, 2004
Table of Contents
Coming in the next segment: Photoshop - Image Compression and Interpolation - What Digital does better than film - Printing - Projecting
