3

We must always lose information when we shoot a photo, whether analogue or digital. But in analogue photography, we have no way of accurately measuring that loss. This is a general characteristic of all analogue media.

In digital media, we choose how much information we are going to capture and throw the rest away.

There are two ways in which we limit the information:
1 - we decide how much information is to be grabbed
2 - then we decide how accurate that information will be

Let's see how this works when we take a digital photograph:

1 - First we limit how much information is to be captured. In my diagram on the previous page, there are only 64 sensors shown - in a real camera there will be millions. The more there are, the more information will be captured and the sharper the picture will be. What doesn't get captured by the sensors is effectively thrown away.
The term used to describe how much information we capture in a digital picture is its resolution. A typical camera's resolution might be given as 4 million pixels. The higher the number, the sharper the picture.

2 - ...then we limit the accuracy of the information captured by the sensors. This needs to be explained a bit more fully:

To produce realistic looking photographs, we measure just two qualities of light - namely colour and shade.

To keep things simple, let's just concentrate on the colour alone.
Instead of trying (and thus failing) to capture an almost infinite number of colours as an analogue camera does, we restrict the number, let's say to just 256. (This number would create poor looking pictures, but it's just by way of example.) In other words, the pictures we are going to produce will be made up from a palette of only 256 numbered colours.
Each sensor in our camera will "examine" the light falling on it and choose a colour from the palette numbered between 1 and 256 that is the closest to the colour being detected.
The term used to decribe how accurately we measure the colour and shade information in a picture is bit depth. A typical bit depth would be 24 bits per pixel. Again, the higher the number, the more accurate the picture.
(If you want to know more about resolution and bit depths, read the notes in Pixels and Pegbars about bitmaps.)

Instead of trying to capture light itself using a chemical process (analogue way) we have changed photography to be the recording of numbers (digital way). 

One thing worth emphasising: doing things digitally does not make them in any way closer to perfection than analogue - a digital photograph can be far worse than its equivalent analogue one. Simply, in all digital processes we first decide how much information we are going to capture, then we give a number to each bit of that information.

If you are with me so far, you have grasped half of the digital story. The second half involves a little arithmetic. Relax! It's very simple and indeed you probably learnt it at school; I am referring to binary numbers.

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