I´m currently on my way in to the deepest darkest tribal regions of Northern India, probably moving very slowly and on an uncomfortable bus, but what to do, huh? So not wanting to suffer on my own, I´m giving you something a little geeky today, but I hope it´ll help some of you understand more about digital photography.

A digital photograph is made up of small dots of colour, it may sound odd but each dot will be made up of a mixture of red, green or blue (known as RGB) each of the 3 colours is known as a channel (RGB obviously has 3 chanels). These dots can be seen by zooming in very close to an image, normally it wint be possible to view the whole scene at the same time.

But how is an image created? well the cameras sensor assigns an RGB value to each of the dots in the image. It will say x amount of red, y amount of green and z amount of blue. these values are numbers between 0 and 255. So each dot will have 3 values, one for each channel, a dot may have the values of Red 22, Green 64 and Blue 195 which gives you a rather nice shade of blue.

For each channel the lower the number the darker the colour, the number zero would be totally black with no detail, similary the number 255 would be the brightest value for that chanel. If all 3 channels are at 0 the colour would be black, if all 3 channels have the value 255 the colour sould be white

Its interesting, and probably easier to understand, if you play with the colour picker here. Simply click a colour to view its RGB value (you´ll need Java installed to be able to use it).

Remember Red Green and then Blue, so the numbers are in that order, note if you click on the most redest of the reds you get the values 255,0,0 this means there are the maximum amount of reds without any other colours, the same for green and blue. Note if you click on the yellowist of the yellows you get the value 255,255,0 meaning it is made up of the maximum red the maximum green and no blue.

So what can we do with these numbers? Well if we group together each dot with the same RGB value they can then be mapped to a graph (also known as a histogram). It is perhaps easier to think of a black and white image that has only one chanel, grey, where zero is black and 255 is white, all other vales are various tones of grey. So a black and white ( or more correctly greyscale) image, if the full tonal range is used, could have 2,000 dots with the value 0, another 8,000 dots with the value 1…. and so on up to 255.

A histogram uses the number of dots as the x axis (verticle) and values 0 to 255 as the y axis (horizontal). You can therefore just by looking at the histogram how dark or light an image maybe.

The graph in the image above shows a grouping towards the left, this tells us the image has many dark dots. As the image show us this is true. So basically you can now tell from just looking at a histogram if the image has more dark or more light dots.

Sorry if this has been a little complicated, it´s a rather technical aspect of photography that many new photographer struggle with, I hope this post will make things a little clearer to some. Check back tomorrow for something better than histograms, seriously – easier to understand too