There’s no doubt that we’re living in the information age – and that for many of us, computers and the internet have become part of our daily lives. With the personal computer revolution almost 15 years behind us, we’ve all learnt to ‘get along’ with technology, and for the most part, we’ve got the basics mastered.
Two of the most fundamental interactions we have with computers and the internet are ‘words’ and ‘images’. By that I mean, mastery of creating and editing text, as well as that of capturing and handling photos.
By all measures, we’re all very well capable of handling the ‘words’ component: word processors are the digital extension of the typewriter, and so expressing our thoughts in written form via a keyboard has been a skill in existence for generations. In fact, most of the terminology used to describe digital typography and the printing processes are directly taken from their analog ancestors.
But capturing photos in digital form and handling the resultant images is a rather new skill – a totally new language is required to describe them, and in this case, the language is most usually derived from a technical basis – there isn’t the same connection to the past as in the written word.
What’s then required is a primer – a toolkit for understanding the new concepts, words and processes that can translate the wonders of image capture, storage and image editing into plain english.
Ready? Let’s go!
What is a digital image?
At it’s most basic, a digital image is a large grid of coloured dots. Just like a chess board is an 8×8 dot grid, so too, images are grids of varying widths and heights, and the dots inside them can be any number of colors, depending on the medium involved.
It’s fair to say that almost all images are either rectangles or square in their outer shape – even an image of a circle will somewhere have a natural bound that fits inside a rectangle.
The number of dots wide and high the image is is one of the most important clues to how detailed the image is. The more dots you have, the more *information* you have, so the more you can convey to your end user.
The second major clue to how detailed an image is, is the dots per inch, or DPI. This seemingly obvious measure of *density* of the dots in an image is often counter-intuitive. Consider two images: one a postage stamp, with high number of dots per inch, say 100 dpi. If the stamp is 2 inches by 1 inch, then there’s 200 x 100 dots, or 20,000 dots in total. But also consider one of those ads on the outside of bus: say the ad is 2m wide x 1m tall, but if you look up close, you’ll see HUGE dots – maybe even 2 or more dots per inch. 2 dots per inch would give you (roughly) 160 dots wide x 80 dots tall, or about 13,000 dots in total. So in fact, while the postage stamp in smaller, it can actually be more detailed than many ads on public transport.
Finally, the range of colours of the dots can vary, too. Printing on a page can be either one colour of ink (usually black only), two colours (typically black plus one other colour), three or even four separate colours. But at four colours, printing on a page usually switches from four separate colours to what’s called CMYK, which stands for Cyan, Magenta, Yellow and Black (K). with these four colours, printers can mix *most* of the colours we’re used to seeing – certainly every colour you see in most magazines.
With physical printing, it’s usually 4 colours or less that make up the individual dots, but with electronic devices (TVs, computer monitors, phone screens, etc) every colour is made up of only three colours: Red, Green and Blue (RGB).
File sizes / camera megapixels
As the above example of the postage stamp vs the ad on the back of the bus showed, sometimes bigger isn’t always better for images sizes. In fact, the only true measure of an image’s quality will be the number of dots it has: the more, the better.
The good news is that if you have more dots than you need, then throwing some away as you make an image smaller won’t matter – but the reverse is not true – if you have a small image, and you try to make it bigger, technology with *assist*, but eventually, you’ll end up ‘making up’ dots. Once you begin to make up extra dots, you’re not gaining anything in image quality, just image size.
That’s why digital cameras are sold with their number of megapixels featured. There are many other determining factors in the overall quality of the captured photo form a digital camera, but if you haven’t got many megapixels to play with, you won’t be able to display your photos beyond a certain physical size.
There’s more maths I can bore you with, but essentially, a 6 megapixel camera ends up with a 6 megaBYTE file size, usually 3000 pixels wide by 2000 pixels high (and for the record, the word ‘pixel’ is shorthand for ‘picture element’, or what we’ve been calling a ‘dot’ in this article).
Now, to fool the human eye, you need colour photos to be 200 dpi or more (ideally 300 dpi) – any less, and the dots start to appear big and blocky – not good! If you were wanting to print a 6×4″ photo, then at 200 dots per inch that is 1200 dots wide by 800 dots high. Since your 6 megapixel camera has 3000 x 2000 dots, you’ve got more than enough, so you’re good to go.
Image Compression
The problem with dealing with lots of images is that the old adage “a picture is worth a thousand words” is actually *true* in terms of file size: you could fit a 200 page word processing document into a 1 megabyte file, but as we noted above, your 6 megapixel camera just gave you a 6 megapixel photo. Ouch.
Images tend to be compressed so that we can manage them easier: on your camera, photos are often saved as a JPEG, which actually ’squashes’ your photo in the same way that you can wring out a wet sponge to make it lighter. The metaphor is accurate, as over time, you re-wet and wring out your sponge, your sponge begins to crumble and fall apart. So too, your JPEG image will compress and lose quality.
JPEG compression is called ‘lossy’, because you do indeed lose quality over time. Other file types are what’s called ‘lossless’, which infers that they do help you compress your images, but overtime, there’s no loss of image quality. Lossless file types are typically: TIF, PSD, and your camera’s own RAW file format.
The important point is that of you want to play with your images, don’t use JPEGs as the ‘working file’ – JPEGs are file for taking photos, but if you’re gong to have a play, do a ’save as’ one of the other file types, above.
A whole new world…
A whole new language to learn – and we’ve only just scratched the surface! Working with images is certainly more and more a part of our daily lives, and with most of my own clients self-managing their own web sites these days, knowing some of the background into keeping images at pristine quality makes them far more self-reliant, and keeps costs to a minimum.
If this is a topic you’re keen to explore more of, let me know via email or the comments, below, and I’ll follow up with more practical advice on keeping your ever-growing photo library in check!
AB out
