Facebook Pixel Scan and Shoot - Resolution

Scan and Shoot – Resolution

What an odd title, you say. Few people ever think about the desktop scanner as anything more than a way to digitise documents but you would be missing out on a whole barrel of talent if you ignored the power of a scanner.

The shame is that, just as I write this message to all you fans of the digital image, the scanner is in the process of being submerged beneath a whole barrage of other functions.

Canon MPC-100 multi.jpg

The multi-purpose device is upon us. Now, for very few dollars, you can buy a device that not only scans a document but copies it, prints it and faxes it.

While these are perfect for the small office and the person who has little need for a high level scanner alone they confuse matters IMHO.

scanners.jpg

I’m a scanner-only sort of feller and can happily sit down with a pile of ‘stuff’ and spend a whole morning just scanning, scanning and scanning. Later on I will make my prints and send my faxes (to be honest, I just gave away my fax machine to a charity shop!).

However I do have many friends who find the scanning business a bit daunting and frequently have early trouble with the matter of resolution.

Right Res

With a computer monitor, the scan resolution determines image size — on screen. This is known as the display resolution.

In my own case, my monitor is capable of displaying up to 1680×1050 pixels. If I select this setting all the on screen items, like hard drive icons, documents I leave on the desktop will be fairly small. In my book, too small … so I use the 1280×800 setting. If I chose an even lower setting, say 1024×768, I find the on screen items are soft edged … not to my liking. This is an important lesson and playing around with your monitor settings will probably teach you more about scanning than many other exercises.

The key element in the whole scheme is that a specific digital image will look far larger on screen than it does on a print. Why so?

Because screen pixels are bigger than the tiny dots that an inkjet printer can imprint on a print.

Look closely at your screen. See the pixels?

Now look at a decent inkjet print. See the pixels? Betcha you cannot!

Basically, the answer lies in the size of each individual pixel and the resolution of the monitor. In my own case (using a Macintosh) I figure the screen resolution to be around 72 ppi (pixels per inch). I know that many Windows users figure their screen resolution at 96 ppi. Others may work with a screen resolution of 100 ppi or more. It’s up to you but the key fact is that a monitor is a low resolution device

The above is important if you scan images for sending by email and only for viewing on a monitor. For one thing, the file size is smaller and, for another, you can scale an image to just the right size on screen.

A printer is a high resolution device. The usual method of printing is to set the image resolution at 300 ppi but you can also go down to 225 ppi and still get a reasonably sharp image.

So, in the scanning process, if you want a final print of 10×8 inches work backwards in your image editing software and, if the ppi figure settles at about 225 or 300 ppi, the print will be acceptably sharp.

CanoScan 5600F_A1.jpg

With current digital cameras you can happily rely on getting heaps of terrific 6×4 inch prints — and even 10×8 inch prints — from the camera’s image sensor, which is often of a far higher resolution.

Back to scanning: open your image in Photoshop or any image editing software or even the dedicated software that came with the scanner, select the final size you want (for email use or for printing) and let the software determine the resolution.

Problem solved.

Monitors are effectively TV screens — video screens — and these are very different to printers. Printers hunger for inches, but monitors don’t care about inches — or centimetres!

A monitor is usually larger than our photographs. Some people often scan at higher resolutions to fill the screen, so increasing the file size but there’s no advantage in messing with huge images; the pixels will be lost when the image is displayed on screen.

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Barrie Smith
Barrie Smith

is an experienced writer/photographer currently published in Australian Macworld, Auscam and other magazines in Australia and overseas.

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