An Introduction to Digital Photography – Session 2. By Paul Emecz. How a digital camera works. Lens Aperture Shutter Image sensor. Lens. Brings light from the scene into focus to expose an image
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By Paul Emecz
Shallow depth of field makes part of an image stand out
Great depth of field keeps everything sharp
When you press the shutter release button of a digital camera, a metering cell measures the light coming through the lens and sets the aperture and shutter speed for the correct exposure. Each pixel on the image sensor records the brightness of the light that falls on it.
When the shutter closes to end the exposure, the charge from each pixel is measured and converted into a digital number. The series of numbers can then be used to reconstruct the image by setting the colour and brightness of matching pixels.
These are drawn from
scratch following a set
of simple instructions.
These are images made
up of tiny squares of
different colours, created
by cameras and scanners.
Spatial resolution is about how small the squares are and therefore how many of them you have.
In essence, the more squares you have, the bigger the file size and the better the picture.
1-bit pictures have only one piece of information – black or white. Grey is an effect created by grouping black and white
8-bit pictures have 256 (28) shades of grey.
12-bit pictures provide over 4000 shades of brightness
A 24-bit image has three 8-bit counterparts for blue, green and red
This gives over 16 million colours!
Each pixel in a 24-bit image has one of 256 values for blue, green and red.
With all that information to store, digital cameras produce large images! When choosing settings on your camera, think about how you will be using your photo:
320 x 525
11,000 x 11,000
The "Economist" magazine says it has 20 million or more. CMOS Imaging News says 5 to 10 million depending on the film. Another source says about 80 million pixels. Robert Caspe at SoundVision states that colour negative film has 1000 pixels per inch while color positive film has 2000 pixels per inch.
? MegapixelsComparing sizes
When you shrink the size of an image, you reduce the quality of the image. This is irreparable – you cannot reverse the process!
Width x height
35 mm film
36 x 24 mm
1024 x 768 (or 800 x 600)
1600 x 1200
6 x 4 inches
10 x 8 inches
If you process a photo that is 1024x768 pixels, and it is being printed as a 6”x4”, you will either receive unwanted white space or lose part of your photo