A scanner does what it says - it "scans".  The idea is to take a piece of paper (hardcopy) and transfer the images and text on the paper into a graphic file on your PC (softcopy).  Scanners are the opposite of a printer :

• Printers take an image file in the PC (or other document file types) and convert it to hardcopy
• Scanners take hardcopy and convert it to an image file on the PC.  

NOTE that scanners can only bring hardcopy into the PC as a bit-mapped image file (a series of pixels, stored as an rectangular array).  They do not bring text in as a text file, or word file.  However, there is software called OCR (Optical Character Recognition) to do this (discussed later).

There are several types of scanners - 95% of scanners are of the flatbed variety :

Flatbed Scanners - the most popular by far, the flatbed is simply that - a flat bed upon which documents are placed, face-down, and scanned

Sheet Fed Scanners - these are basically a flat-bed that contains a mechanism to feed sheets through, much like a printer can feed sheets through automatically.  There are quite a few printer/scanner devices on the market that do both, and use the same feeder mechanism

Photo Scanners - similar the sheet fed scanners, except they are made specifically for photos, and the feed mechanism is small.  Also, the typically use high-resolution scanning only

Card Scanners - these have one function only . . . to scan business cards, and they come with software to catalog and store the scanned business cards

Hand-Held Scanners - the most reviled of all scanners - they are a handheld device, and rely on the user to move the device across the paper, with a very steady hand.  These are often called half-page scanners because they can only scan 2 to 5 inches at a time. Hand-held scanners are adequate for small pictures and photos, but they are difficult to use if you need to scan an entire page of text or graphics. 

Scanner Hardware

Since the flatbed scanner is by far the predominant variety - we will discuss that here.  I removed the cover - to reveal the inner workings of the scanner.  You can see in the image below, that there is a guide bar on the left, which the scan head slides along.  Below the guide bar is a black rubber belt, which pulls the scan head along.  This scanner is 8 1/2" by 13", which is much preferable to the more common 8 1/2" by 11".   The image shows the scanner in action.  You can see the ends of the light bar (the middle portion is shining upwards - but is obscured from this angle), as well as the electronics that reside in the scan head.  The apparatus moves along, viewing the bottom of the document, and sending data to the PC.

This next picture was taken from the a direct top view, in order to show you the light bar.  The black slot just above the light bar is where the row of  CCD's (charge-coupled devices) reside.  The CCD's are like tiny eyes, and view the image, while at the same time, transmit the image as a series of dots to the PC

The Interface  -  Parallel vs SCSI vs USB

Parallel - a couple of years ago, most scanners for home use, had a parallel interface - the same as your printer.  This is actually quite slow, especially with high-resolution scans.  In addition, you needed to daisy-chain your printer, and plug it into a parallel port on the back of the scanner.  This has caused a huge number of headaches.  It usually works OK - but many printers have had problems sharing their interface in this way.  In addition, many scanners would only work with faster parallel interfaces such as EDP or EPP, and the user had to update the Windows driver for the parallel port - which can be tricky.

SCSI (Small Computer System Interface) - excellent, and very fast - however, you do need to invest in a SCSI card.  Unlike the other two plugs shown (which are both the PC end) - the SCSI cable shown is the end that plugs into the scanner itself.  It is a full-size, 50-pin SCSI connector - in most cases, the opposite end that plugs into the SCSI card is a small 50-pin mini-connectors as well.  The SCSI card is very narrow and cannot accomodate the full-size plug - plus, it applies a lot of weight and could damage the port or the solder points inside the card, so they use the mini-SCSI connector.  

I prefer SCSI over parallel for obvious reasons - it is much, much faster.  But I also prefer it over USB, because most PC's only have two USB ports, and they can fill up quickly with other devices.  Also, the fastest CDR's (CD Recorder) are SCSI, so I bought that flavor - the SCSI card can accommodate up to 7 devices, so I was able to run both my CDR and my Scanner from the SCSI card.  I probably cannot recommend using a SCSI scanner for most people, because it is a bit tricky to set up.  If you are even slightly technical, however, you should do fine.

USB (Universal Serial Bus) - the recent crop of scanners often come with a USB port, which I believe is the way to go for the masses.  It is fast, and it does not interfere with the operation of your printer.  Unfortunately, most PC's come with just two USB ports which can quickly fill up (printers, digital camera flash card readers, etc.).  You can buy cards that have 4 or more USB ports, if you need more.  The "Plug and Play" properties of USB are superb - just plug the scanner in with your PC on . . . and it will automatically begin installing the drivers, and request the CD to be inserted.  Keep in mind that there are a few different methods of doing this, so follow the manual closely.

Overview of an Actual Scan

1)  Place the Sheet - you place the sheet of paper face-down on the glass plate, and lower a cover on top of it.  The cover makes sure that the paper remains flat, and also, since it is white - it prevents ambient colors and light from entering the scanner.  

2)  Open Graphics Application - the open Scanning Application within - the user opens an application that can communicate with the scanner.  All scanners come with low-level, software to allow the user to scan with.  All good professional image applications, such as Abobe Photoshop, can communicate with the scanner through the use of a standard software scanner interface, called "TWAIN".  TWAIN, oddly, is not an acronym for anything.  In many cases the actual scan routine will be opened within the graphics application, when you start the TWAIN drivers.  In this example, a Microtek ScanMaker E3  is being used with Photoshop.  After Photoshop is opened, the user clicks File/Import . . . Twain32, and the Scanmaker Sanning Wizard opens, as show below.

Note that there are a number of settings in the dialog box on the right, such as Colors, Resolution, and descreening.

3)  Configure the Settings - you may as well scan using as many colors as possible.  The resolution setting is very important, and will be discussed later.  Descreening is critical, and necessary for most scans - except photographs.  Most hardcopy is printed material from magazines, or printers - and has thousands of tiny dots.  These dots, when scanned by a procedure which makes more dots, has a "screen effect" - which results in a grainy image.  Descreening smoothes the grain. The other settings, such as Highlight, exposure, etc. - are best left alone, unless you find that your scans are not coming in well, and in that case you may need to run a series of test scans, tweaking these settings until you get them right - the next time you scan, the last settings should automatically appear. 

3)  Preview - in order to see where the portion you actually want to scan, is located on the faceplate - most scanner applications come with a "preview" button - this causes the scanner to move very quickly, vertically, and scan the image with a very low resolution - grainy scan

NOTE:  I do not use preview, since it is an unnecessary step - it is easier to size the scan larger that you need it to be, and then crop the excess after you complete the scan

4)  Size the scan - there is usually a rectangle of white dotted lines on the preview, which dictates the area that will be scanned.  This can be moved so that the actual scan will not include unwanted areas.  A high resolution scan at 300 dpi can create a file upwards of 30 MB, and can take several minutes to complete.  If you have placed a small 3x5" photo on the flatbed - you certainly do not want to scan the entire area (even though you can subsequently crop the unwanted areas off with the software).

To reposition the dotted-line rectangle, you move the mouse anywhere inside of it, and click-drag.  To resize it, move the mouse to the corner (until the mouse pointer turns into a double-arrow) and click-drag. 

Note :  the preview will look very grainy, since it is just a quick - low quality scan.  When you perform the actual scan it will be clear.

5) Scan - click the Scan button with your mouse, and the scanning begins.  A horizontal beam of light moves slowy down, from top to bottom, while at the same time, a row of CCD's (charge-coupled devices), reads the reflection and sends lines of dots to your PC  -  once the scan is completed, the series of dots in lines, has created a rectangular array of dots, which are stored by the PC as a graphic file.  

6) Manipulate the File - there are a number of image file types, but the most common used by scanners is jpg (JPEG), tif (TIFF), and bmp.  For example, you scan a hardcopy, and in the application you may see 0001.jpg, and then your next scan would be 0002.jpg, and so on. The initial scan will rarely appear exactly as you wish.  There may be further cutting of edges (called "cropping"), as well as changing the contrast, brightness, color saturation, etc.  In the case of this example, I first cropped the image, since I only wanted the picture of the PC - and then applied a great filter called "Levels" (similar effect to adjusting Brightness and Contrast - but has better results), and  finally, increased the sharpness of the image.

NOTE:  this scan is poor, since the original stock was a thin, sheet from a magazine.  If you scan images from books, or high quality magazines - the results are much better.  For example, here is a portion of a scan I did from a beautiful travel book, of a curio window :

Sample - here is one of my favorites, of a Rich Man's manicured back yard in the mountains - a full, 1024x768 scan taken from the same book (1348 kB) - the original scan was done at 300 dpi - the results are  stunning.  I have done hundreds of these scans, and created a CD for friends and family for Windows Wallpaper.  I scanned, cropped, manipulated for optimal look, then sized them at 1024x768 (a common screen resolution) - and also made a series of images at 800x600 (another common screen resolution).  This is so much cheaper than purchasing high-res images online (Corel charges 30 bucks apeice).  With your scanner, and a purchase of a couple of $30-$40 coffee table books, you can create your own personal library of stunning images :

High-Res Scan Sample  (to download, right-click on image after it opens)

The scan was done on a $150 Microtek ScanMaker E3, yet has incredible detail.

7) Store the Image -  Typically, the files at this point are only temporary - of you do not save them, and close the application - they are gone.  Therefore, you would click File/Save As . . . and save the file (0001.jpg) as whatever name you choose.

Resolution PPI vs DPI

Scanner resolution differs from printer resolution in regards to how it relates to the PC's pixels per inch (ppi).  

Should I change the dpi (which is actually ppi) after scanning ??  depends on what you will be doing with the image.  If you just want to save family pics on your PC for viewing on your PC, then there is no need to mess with the dpi.

Scanners, Printers, Monitors, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.

Scanner resolution differs from printer resolution in regards to how it relates to the PC's pixels per inch (ppi).  

• with printers - dpi is not related to ppi at all - DPI is a setting that you can change within the printer "Properties" dialog box, that is available as an option whenever you select File/Print in any application (you will see a button for it - but do not need to change it normally).
  
• with scanners - dpi is the same as ppi - it is a setting that you can change.  Then when you scan in the image, it is stored as an image file, which has a ppi setting that is equal to whatever dpi you selected !!  

Forget about DPI unless Printing - in reality, the industry should have never referred to scanned images using DPI.  DPI has always been a term used solely with printing.  Scanners use ppi, since they bring in an image as a bitmapped image file, and ALL bitmapped images have a resolution that is ALWAYS measured as PPI. 

The best way to think of your scanned images is to use PPI and just forget about DPI unless you are dealing with printing.

If printing - and you have enoguh disk space, make sure Scanner DPI = Printer DPI:  if you are thinking of printing, and plan to print the scanned image - then it is best to scan the image at the same resolution as you will be printing it at (typically 300 dpi).  However this does create huge files, so if you will be saving the image, then just go ahead and scan it a a lower resolution such as 150 or 96.

So with scanners, dots do equal pixels !!  Remember, with scanners, dpi=ppi !!  If you scan a 4x4" image at 72 dpi, and your screen resolution is set to 72 ppi, then the image will take up 4x4" on your screen.  However, often, it is better to scan at higher resolutions than that - especially for high detail nature images, or people.  Therefore - the resultant image on your screen will be huge, and you may be only able to see a small portion of it at a time.

I believe, in general, you may as well go ahead and scan in high resolution - I use 150 dpi usually, and use 300 dpi for the large, nature images that I scan for Windows backgrounds.  It does result in a huge file size - 10 MB up to 30 MB.  However, you will be reducing the image size after the scan, within your software - through "resampling".

The problem of scanning at lower resolutions - even if that is the final resolution you want - is in the resizing.  Resizing a huge image to a smaller image results in clear, fine detail.  Resizing small-to-medium images always degrades the quality substantially.  For example, a 100x100 image, resized to 90x90, has to use a very small number of pixels, and interpolate them to the new size.  Conversely, a 1000x1000 image, resized to 90x90, has thousands of dots to work with in it's interpolation algorithm, and can much more accurately depict the final image.

You lose nothing by scanning at high resolutions - just adds a short amount of extra time to the scan.

Should I change the dpi (which with scanners is really ppi) after scanning ??  depends on what you will be doing with the image.  If you just want to save family pics on your PC for viewing on your PC, then there is no need to mess with the dpi.

Remember, the ppi of the image is only a value used when the image is sent to the printer.  "Some" applications, such as Word, will display images as WYSIWYG (What You See Is What You Get), which means it displays exactly what will come out on the printer.  So Word will show a 300 ppi image that is 200x200, as being smaller than a 72 ppi image that is 200x200.  

Microsoft Word image Sizes and Printouts

• In general - Word shows what will come out on the printer !!
• In general - the Word ruler shows the width of what will come out on the printer
• In general - Word does NOT show the same size on the screen as the ruler or the printout shows.  The size on the screen is a function of your display settings (i.e. 800x600 vs 1024x768, etc)
• Exception - if the inserted image will not fit the width of the page in Word, it resizes it DOWN !!!  In this case the dimensions in Word will still match the printout - but the dimensions do not match the image ar all since it has been resized

All image viewing applications, and for that matter, most computer application, ignore ppi - it is a printing concept only !!  The only parameters that your PC cares about, when displaying an image, is the dimensions of the image in pixels (Width x Height).  

Changing the Display Size and/or Print Size of an Image

to make the image appear on your screen in the size you want, you must "resample" it, using Photoshop or some other image editor - to the lower dimensions that you prefer.  

to make the image appear on your printer ins the size you want - do not resample - instead, using Photoshop, go to Image/Image Size, uncheck the "Resample" box, and change the ppi - you will see that this effects the "Document Size" (the print size):

Computers ignore PPI !!

Here is proof that the PC ignores the ppi of an image - these images also appear in the Monitor 2 section, since it is a very important concept - which few understand.  Feel free to download these by right-clicking on them, and open them in an imaging application.  You will see that they are at 72 dpi and 300 dpi respectively - if you insert them into a WYSIWYG application such as Word you will then see their size differs greatly, because Word shows you the size that they will print out at.  Nevertheless, the dimensions of both are 200x200 pixels, so they are identical on the screen, and the files sizes are also identical (each is 15 kB) :

  Image1 - 200x200  72 ppi                                 Image2 - 200x200  300 ppi 

*** these look the same here because Web browsers are not WYSIWIG for images - they display the image at it's dimensions - and ignore the ppi.  

So how will these print?? (my printer default to 300 dpi)

Image 1 should print out larger than Image 2, because it is less "dense".

Image1 is 200x200 pixels, at 72 pixels per inch, and therefore it will print out at a size of 200/72 = 2.77x2.77 inches.  Since the printer lays down 300 dots of color per inch, this image prints at 2.7 x 300 = 833x833 dots.

Image 2 is 200x200 pixels, at 300 pixels per inch, and therefore it will print out at a size of 200/300 = .666x.666 inches.  Since the printer lays down 300 dots of color per inch, this image prints at .666 x 300 = 200x200 dots.  Does 200x200 sound familiar?  Well, the ppi of the image = the dpi of the printer.  Therefore the printer prints out the image with the same number of dots as there are pixels.

OK - then prove it !!  Print them !!

No problem.  I printed both, tore off the excess paper, and took a snapshot so you can see.  Even though the printer is "set" to 300 dpi, it does take note of the image ppi setting, and the image dimensions.  It printed both of these these at 300 dpi, which is the preset physical number of sots it will lay down per inch.  But it sized the images according the their ppi (72 and 300 respectively).  

When you send a job to the printer, it will send it at whatever dpi you have configured in the printer "properties" box.  That is a "physical" concept, and the 300 dpi is just the density of the print job.  The printer will also look at the ppi and the dimensions of the image, and size the job accordingly.

NOTE:  since all printed images are sent to the printer at a high resolution (most printers default to 300 dpi and have options for 600 or even 1200 dpi), it would seem that it is best to use images that have a ppi equal to the dpi so that no conversion will take place (conversions generally always result in at least some loss in quality).  But in "general", so long as the image is crystal clear on the screen - it should be crystal clear on the printout.  For small, detailed jobs, however - such as business cards, you should use a ppi equal to the dpi of your printer.  300 dpi is more than enough for any image IMO !!  Print shops make their $$$ based on quality - so they would never think of using images at 72 ppi.

Using your Scanner as a Photo-Copier

Some scanner software has a photocopy function, but it basically only works for copying a full 8 1/2" x 11" sheet of Letter paper.  The method is simple, scan and then print.  Her is how you can do it manually, using Photoshop as an example :

1)  scan the image at a high resolution (150 dpi to 300 dpi)

2) crop, and manipulate brightness, contrast, sharpness, etc.

3) goto Image/Image Size . . .

4)  you will see the Print Size listed.  To get it to the size you want, uncheck the "Resample Image" box, and begin entering new values in the print dpi box.  If you lower the dpi, the print size increases, and if you increase the dpi the print size decreases.

5)  Once you get the print size to a value you want, click OK to accept the settings, then print the image.

OCR (Optical Character Recognition)

Few people use OCR.  Most scanners come with a limited version of OCR software, and the chance to upgrade, for a fee, to the full version.  My scanner comes with a 25-use trial.  Instead of paying the 200 bucks for the full version, I rarely ever need it, and have only used it about 5 times.

OCR is useful for one thing - when you have a hard copy of a text document, such as a newspaper or magazine article  .  .  .  or perhaps some old documents which the soft copy has been lost  -  and you need to bring them in as a series of documents.  If you leave them as bit-mapped graphics, the file sizes are huge, and cannot be combined.

When you run the OCR software on these documents, it converts them to text documents (usually Word documents).  The conversion almost always creates errors.  The software comes with an accuracy rating - usually 95% to 99%.  Therefore, after running OCR on bit-mapped images that you have scanned - you need to proofread them and edit out the errors.

What Scanner should I Buy

Only one I will ever use -   the Microtek Scanmaker E3, or E3 Plus. Simply superb  .  .  . clear datail, vivid colors, simple operation, great Twain drivers, and an easy-to-use interface with great descreening for magazine and book scans.

DO NOT BUY ANYTHING MADE BY MUSTEK !!

DO NOT BUY HP SCANNERS !! Good scanners, but they have very glitchy software and drivers, called "paper port" - steer clear of it.