A4 scanning tutor

As an introduction to one of the PROCESS's on line courses we offer you this look at good A4 flatbed scanning.

accepted , the images in this exercise are not ' perfect ' but that is due to the high compression to keep our downloads RAPID, not because of the scanning ( then again bad scans don't compress)!

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A4 flatbed scanners are now so cheap that most people, who want too, have access to one.

The quality of output, in the main, is determined more by the user than the manufacturer.

A 4800dpi scanner may seem to offer better image quality than a 1200 dpi model but is that really true?

In the following workshop I will explain some of the more common mistakes that occur with ,'scanned images'.

Following this simple exercise you can almost guarantee that your on screen images will be as close as is practically possible to your original source image everytime.

TRUE

If you intend to use your
images only on screen it is
unlikely that you will ever
need a scanner that
produces higher
resolution than 300dpi

FALSE

The higher the resolution
you scan at, the higher the
on screen image quality.

( It
can actually get worse)!

FALSE

There is only one setting
on my scanner, it is
Millions of colours!

FALSE

It is necessary to scan
at high dpi's in case I
need to print it out at a
later date!

FALSE

The average person can
notice more than 80 greyscales

First of all it has to be decided for what purpose the scan is being made. This is usually for one of two reasons:

Inclusion in a DTP document or for images on screen; such as your website or multimedia presentation

In this exercise we will concentrate on output method No.2

1.) If your primary output is to a DTP package the resolution of your scan will need to be determined by a.) the output printing device b.) the degree of image enlargement c.) the quality of output necessary for the publication. d.) the size and nature of your file storage and distribution system.

2.) If your primary output is to the screen, for multimedia and/or website design your primary concern is going to be onscreen image quality and file size. The latter probably being the deciding factor.

Producing high quality screen images in small files is a real skill, and one that must be mastered if you wish your Home page to download on the same day as your visitor arrives! We have all visited a 1Meg per image site at some point.

No web image need be bigger than say 100k and many need not be more than 20K.
So how is it done? Follow the steps in this example exercise and you will be there within the hour!!

I have abbreviated the text to save reading time, I figure that by now you have had enough of my prose and would prefer a bit more substance and a little less chatter. Any problems, just send me an email and I will do my best as-soon-as-poss.

Step1. Decide, in pixels, how large your image will be on the screen. Pixels are the best units to use when plotting images to the screen. The most common screen dimensions are: PC 800 x 600 also 640 x 480 An example size may be 165 pixels x 256pixels.	Step 2. Next you must decide the screen resolution. These are typically: 72 dpi on a Mac 96 dpi on a PC The scan resolution you choose need not be higher than this. Your monitor would not display it any better even if you did!	Step 3. Decide on the colour depth. Most scanners will give you at least three options. a.) 256 greyscale b.) 256 colours c.) 16 Million colours. Many scanners will give you more options such as :thousands, millions,line art, 16 colours	TRUE The human eye can see approx. 16 million colours and NO more. It never however sees them all at once! It is very unusual for you to experience a scene with more than a few thousand. Consequently you may well find that an image scanned at 256 colours (or thousands) will not look much different too the original and the file size will be much smaller.
	Scanning the image at the right pixel size is vital to successful image manipulation. You must decide before you scan what dimensions the image scan needs to be. In this case the image is, 165 x 256 x 16Million colours. Depending which model of scanner you have and the software it is supplied with will determine how you execute this..	Step 4. Using a typical, good quality scanner, in this case a UMAX 6E which is TWAIN compliant, the scanning software allows you to make a pre-scan. From the pre scan select your image area. This will give you a default image size.Now... a.) set your COLOUR DEPTH. b.) Your IMAGE resolution,100 dpi (this is usual for 72 &96 dpi screens)	Step 5. Now alter the PERCENTAGE (%) magnification until the image SIZE is exactly what you require. You may well have to do this manually from the ...othersize option. Remember that the ratio of your image may be different to the size you require. ie you can get one dimension right but not the other! In which case you must decide which dimension is the most important and change the selection area until you get the exact dimensions you want. DON'T COMPROMISE
Step 7. When it comes to colour balance I have almost always found that the AUTO setting will give you the best colour/brightness balance, especially if you are taking only a selected area of an image. Remember virtually all paint packages will allow you to modify the colour/brightness etc. later on. If however the balance is wildly off you may need to either: recalibrate your scanner or tweek the manual settings.		Left Images scanned to size will give you crisp accurate text and detail. If you need it bigger...re-scan it! right resized images break up badly like this; notice the text

Manipulation in Photoshop, Paint shop Pro etc. is great fun and creates dynamic images (eat your cheese Dali).

But you have to start with the best image you can.

Now you know how.