If you are serious about using images in presentations you should consider buying a scanner. We realise that not everyone needs or can afford a scanner, so in this chapter you will also learn how to get digital images of X-rays, transparencies and other objects without a scanner.

If you want to scan your old 35 mm slides, you will need either a dedicated film scanner or a transparency adapter for a flat bed scanner. Realistically, unless you are going to do a lot of scanning, you would be better getting your best 35 mm slides scanned professionally – most high street camera shops will do this (at a price). Once your whole collection is scanned and saved to a CD you can forget about slides forever!

If you want to scan images, such as pictures from a book, you will need a flat bed scanner. If you are planning to scan X-rays, you will need a special type of flat bed scanner that provides light from above the X-ray – a transparency scanner. Be sure to buy one that has a large enough plate to accommodate a full size X-ray.

If you are a radiologist or do a lot of teaching using X-rays, it will be worth investing in a transparency scanner, but for most people there are ways to get around this problem that will do. Of course if you are lucky enough to work in a hospital with a digital system, the radiology department will output image files on disk for you. You can learn how to do this in the next chapter.

For most of us, the best buy is a flat bed scanner. Flat bed scanners are useful for documents, images from books and even solid objects. The image shown here was scanned using a relatively cheap Epson scanner.

The image isn’t on the PDA, it was added as an extra layer (you will learn how to do that in another chapter).

A word of warning if you are considering buying a scanner; the resolution of the scanner may be described as “interpolated” or “optical”. Optical resolution is the true resolution. You will remember that interpolation is a software technique to fill in the gaps between pixels by guessing what colour they should be. It is not a true reflection of the capabilities of the scanner.

Of course a flat bed scanner is much more than just an image input device. Modern OCR software allows the computer to recognise the text on the page and reproduces it in a word processing program – OCR stands for optical character recognition. The scanner may also come with software to archive the scanned files. One of the best of these is PaperPort from ScanSoft, but there are many more.

Before we can discuss how to scan images and X-rays, we need to consider how a scanner works.

How scanners work
Most flat bed scanners are TWAIN compliant; what on earth does this acronym mean? Well in this case, actually nothing! It is said to stand for “technology without an interesting name”! What it really means is that it is compatible with almost all image manipulation software, and in particular Adobe Photoshop Elements.

The image or object to be scanned is placed on the top of the glass plate on the scanner. The lid is usually shut, but can be left open, which results in a black background. When the software on your computer tells the scanner to start scanning, the first thing that happens is that the lamp warms up. This may take several moments. The scanner then moves underneath and parallel to the glass plate and pre-scans the object.

As it does so a light also tracks under the glass plate to illuminate the object. The reflected image is collected and redirected by a prism, which send it to a CCD (charge coupled device exactly the same as that in a digital camera). The digital signal from the CCD is sent to the software for image acquisition.

Scanning using Photoshop Elements:
Place an object on the glass plate of your scanner, open Photoshop Elements and select “Connect to camera or scanner”.

In Photoshop Elements version 1 the choice is “Acquire” If this is not visible, use the command File>import>twain.

Next choose a TWAIN source. Usually you will have only one – your scanner. However, if you have a video camera (web cam) some other input device, this may show up. You will now find that the scanner pre-scans the glass plate and you acquire an image like this.

Image type:
To the left of the scanned image there are a series of choices. We now need to go through each of the settings so that you can choose the optimum settings for your scan.

There are six possible types of image. These are colour photo, colour document, black and white photo, black and white document, illustration or text / line art. These are fairly obvious, but what difference do they make. While it is tempting to ignore them, don’t!

The settings “colour photo” and “colour document” scan the object recording the primary colours (red, green and blue) for each pixel of the image using one byte for each channel (8 bits for each, so a 24 bit image). This will be three times the size of a black and white image, which scans using one byte for each pixel (8 bit image). So, if you are scanning a black and white image, or if you are scanning a colour image but want to save it as a black and white image, choosing black and white photo or document will reduce the file size to one third of the size of a colour image.

The difference with “document” (whether colour or black and white) is not to do with bit depth (8 or 24) but to do with something called de-screening. When an image is printed and then scanned (for example from a book) the resulting image will have a Moire pattern. This is a curious herringbone like pattern that results from the printed image. This is removed by de-screening. You can do this manually by scanning at very high resolution, blurring the image just a little and then sharpening it again using “unsharp mask”, but Photoshop just does it for you, so why bother?

In the scanner setting “illustration” colour smoothing is activated. Simply put, this reduces the number of colours that the scanner detects in an image and this is applicable to images that are going to become GIFs (only 256 colours).

Sorry, that is all we will tease you with. To learn more and too see the other 7 images that walk you through this you will just have to buy the book!