ELECTRONIC IMAGING

 By Dennis O'Connor (Area 20)  

Before We Start. You must realise that electronic imaging cannot (at the time of writing this lesson) compare in any way with 35mm photography. This is not the fault of the operator, it is to do with the limitations of the equipment employed. All scanned images on a computer are made-up from a large number of `dots'  or `bits' and called `Bitmap' images.  It does not matter what the shape of the original article was `line' `box' `circle' `text' `photograph', they will all be broken down into and represented by dots. So, do not try and compare a screen image or a printed copy of a scanned colour photograph with the original, you will be disappointed. 

Scanning Images. Any image may be scanned using an electronic scanner. However, the type of image `text' `line drawing' `photograph' will usually determine the most suitable application. 

Two examples might be: a photograph would probably be used as an illustration. 
2. text could be scanned as text for optical character recognition (O.C.R) or it could be left as an image and used as a graphic. 

System Requirements. As a Minimum you will need a `fast' computer with lots of memory and a big hard disk if you intend to do serious scanning, an example might be. At least a 486 computer with 16 megabytes of RAM fitted with a very fast 1 gigabyte hard disk and `true colour' colour monitor. Although it is possible to scan with a more basic machine it will probably prove to be very time consuming, and limited in the variety of scanning you could do. 

Scanner Types. 

Scanners vary in style and scanning resolution. 

Hand Scanner.  These have to be drawn across the image to be scanned.  There can be a problem with the scanner `twist' moving out of line and distorting the image, and they tend to be slow.  An A4 page would have to be completed in more than one scan and `stitched' together. 

Sheet Feed Scanner. These are capable of accepting an A4 page, but as the page is fed into the scanner it can `twist' and distort the image. they can only accept single sheets fed manually into the input rolls.  

Flat Bed Scanner. The most widely employed type. They can accept single sheet, or can have a document feeder attached to allow automatic feeding and scanning of multiple pages. Books may be placed face down and have the page surface scanned. Since the scanning head moves inside the case, not the document, these scanners offer the best results. 

The majority of scanners are now colour models, and unless you are only ever going to output monochrome (black and white) the best choice are the colour versions. They range in scanning resolution from 100 dpi to 1,500 dpi. However as you will read later in this lesson it is very unlikely that you would ever need to scan at anything over 200 dpi. 

The exception to this would be if you are scanning photographic negatives, when a high resolution does really become necessary. The important feature of any scanner is it's `Optical Resolution'. This the actual rsolution of the scanner without any enhancement using software to increase resolution artificially. This feature is called `Interpolation. or `smart sizing'. 

The Image. When you decide you are going to scan an image your considerations must include the following:What is the size of the original image and what will the output size be?
It is possible to `scaleÆ an image to a different size from the original e.g. 100mm x 100mm photograph.
Scale 150% will give an output image size of 150mm x 150mm.
Scale 75% will give an output image size of 75mm x 75mm. 

Note. If you decide to scale an image, there is a price to pay!  This is covered in the next section. Will the image be a black & white line drawing, a black & white photograph or a coloured photograph? 

A line drawing will require the least amount of memory to scan it. Since it will only be using 2 colours `black or white'.  

A black and white photograph would not scan successfully as just black and white (except for special effects). It would have to be scanned as a number of grey values. That is, the picture would be interpreted as consisting of `Black' `White' and all the shades between would be divided into shades of grey. You might decide to use 64 grey scales (shades), or for photo realistic results 256 grey scales. 

You can only output a true `quality 256 grey scale' if you printer has a resolution of 2000 DPI or higher! Incidentally, laser printers cannot `print' grey scales, they can only simulate them.

Colour photographs require the most memory if they are scanned as colour images. 

Colour photographs can be scanned as: 

16 Colours. The image is reproduced in 16 colours only often with poor results.
256 Colours. The image is reproduced in 256 colours. This gives better results and is often sufficient for most D.T.P applications.
16 million Colours. The most realistic reproduction, but if your equipment is not capable of displaying or printing them all it is a waste of resources. This resolution is normally employed for `Professional' publications and `Bureau' work. 

Coloured images can also be scanned as `grey scale' images. If you are going to print the result in `black and white' there is no point in scanning in colour, it will be quicker and require less resources. Also, if you view a coloured image on a screen, you will not see an accurate representation of the output. This is because the printer will print a given colour as a shade of `grey'! 

Scanning Resolution. The significance of the scanning resolution cannot be over emphasised! There is no point in scanning an image at 1,000 dpi if you can only print at 300 dpi or 600 dpi. In fact there are definite advantages to scanning at resolutions below your output maximum. Most images (not OCR text) can easily be scanned at 100 dpi without a loss in quality. Photographs to be printed on an Epson `Stylus II' at 720 dpi only need to be scanned at 200 dpi! 

Following is an example of a colour photograph of a seascape, scanned at 150 dpi converted to 256 grey scale and printed at 720 dpi on an Epson inkjet printer. 

There is another point to bear in mind when you are selecting the scanning resolution, and it can be a difficult concept to grasp initially. It is this. For any image size. If you double the scanning resolution You Will Quadruple The Size Of The Resulting File!!! 

The Seascape 

As an example of  the effect of scanning resolution on file size we will set-up a scanning session using a photograph and see the resulting file size as we select different scanning options. 

Original Image 16 million colours scale 100% File Size = Original Image 256 colours (colour photo) scale 100% File Size = Original Image 256 grey scale (black & white photo) 100% File Size = Digitising. 

This is very similar to scanning except a special `Interface Card' and an associated program replace the scanner. This card fits into one of the expansion slots inside the computer and can be connected to: A `Digital' still camera. To `capture' the image the camera lens views. 

A `Video' camera. To `capture' the image viewed by the camera lens.  In this case the image may be `moving' and a pre-determined number of `frames' may be captured. 

A `Video' recorder/player. To `capture' the image stored on the video tape. In this case the image may also be `moving' and a pre-determined number of `frames' may be captured as with the video camera, or the `freeze frame' may be used to capture a single frame. 

Although the quality of the image is improving as technology is advanced, at present the quality is only suitable for `Non 35mm' applications. By this I mean that the resulting images are suitable for the majority of D.T.P applications, but, without enhancement by an experienced operator they are not suitable for `professional' publications. 

Digitising is an ideal way to capture screens for `presentation' applications, since the input `capture' quality will be similar to the `presentation' quality as they will both be viewed on a screen (TV or Computer). Most of the `capture' system resolutions are calculated on the screen resolution, and you can select the resolution you think most appropriate to the task. Like everything, you only get what you pay for! A very expensive digitising system will produce results requiring the minimum of enhancement prior to use by Newspapers and/or magazines. 

Black and White or Colour? If the image is for screen output you can use colour without additional costs, providing the output screen is capable of showing all the colours you have digitised at. If the output is for D.T.P then black and white would probably be a better choice. Just because you are digitising does not release you from the effect of `file size'. A digitised colour image will require more room for storage than a grey scale one. Ensure that the digitising system is compatible with your system before you install it. 

One final point. Not all digitising systems will capture colour from a moving image. You may have to invest a lot of money to achieve the results you would like.

Photokina 2000

Editorial

CRCMain