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 Scanning 101  Part One  Here
 Scanning 101  Part Two  Here
 Scanning 101  Part Three  Here
 Scanning 101  Part Four  Here

 

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Scanning 101 Part Two

Now that you have a scanner, how does it work? They look simple enough from the outside but under the glass is where the magic begins. In this article I want to explain what makes a scanner work. Scanners all basically work the same way. They measure light that is reflected off the subject image. How they do this is with a light bar and many tiny sensors. If you have a flat bed scanner the light bar is the only moving part and sits just under the glass. Upon scanning this light bar will move from one side to the other to light up the entire image. Tiny sensors also known as the array, collect the reflected light. The smaller the sensors the better the resolution as we know it will be. This is where we hear that the scanner is a 300 dpi. Dots per inch is determined by the size and amount of these tiny sensors. Todays standard flat bed scanners are starting at 600 to1200 dpi.

Reflected light from a single dot in the image is picked up by one sensor. This sensor determines the intensity of the reflected light. Every sensor produces an electrical out put which is read by the computer. The computer determines the intensity of the reflected light and produces in dots per inch data.

The use of hand held scanner are no longer used because of their instability to capture complete information. This scanner read line per line over the image. If the scanner was moved over the image to fast with a slow computer a crash was likely. Computers today are very fast but technology has moved towards the use of the flat bed which uses a motor to move the light source. If the computer is slow the motor will slow or stop to let the computer catch up. Some scanners come with a buffer which will allow the scanner to continue while the computer reads from the buffer at its own speed.

Scanners are sold in SCSI, Serial, USB, and now Fire Wire connections. Although SCSI is faster than a Serial connection, in Photoshop most scanning speeds were about equal. SCSI is faster than USB and Fire Wire is faster than all three but cost waymore too. The majority of scanner connections are serial, SCSI and USB. Firewire is more for the professional who is doing large file size and needs the speed. Remember this, the higher you scan your image this is where you determine how much dpi you will scan you image at. The more dpi the sharper and in focus your image will be however the data size will be larger also and the computer will work harder and longer too. At 300 dpi an 4 by 6 inch image could be well under 1 meg. The same image scanned at 600 dpi could well be over 5 megs. So determine what you need and what you need the image for. Text can use a lower dpi such as 300 dpi of less. Black and white images can use a 300 to 600 dpi. Color can use a dpi of 600 or more depending on the detail need from the image. Pictures scanned for a web page do not need to be more than 96 dpi for the windows and 72 dpi for the Macintosh. Most compression software like adobes, "Image Maker" included with Photoshop 5 will reduce any scanned dpi to fit for the web. With the reduction in dots per inch comes less noticeable picture sharpness which can be corrected with any imaging software.

Now back to what makes a scanner tick. There are good scanners and bad. There are expensive scanners and cheap too and believe me you get what you pay for. The light source has a significant role of the quality of the scan.The spectrum of colors in the light should be uniform. All colors of the spectrum will be emitted equal. With a light source which gives off a lower intensity of light will emit spectrum colors of variable intensity. This difference is noticed more in color scanning than with black and white scans.

When the light of the scanner passes once across the image it has actually scanned 3 times. Each of the three primary colors levels: Red, Green, and Blue have also passed over in the single pass. This is why you can acquire a combination of up to 16.7 million colors after just one pass. But why stop there scanners of yesterday ran 24 and 30 bit and now are running 36 and up. The higher the bit the more colors that the sensors can detect.

Unless your using your scanner to reproduce images for magazines you do not have to go to the extreme when buying a scanner. Scanners today are cheaper so watch out for what you are paying for. If you are using it just for web graphics than look for a 24 bit 300 dpi if you can still find one. The most common are 30 to 36 bit 600 dpi scanners for a good over all scan. Even the 36 bit 1200 dpi scanners have come down in price. Use the internet to find out the specs and software of the scanner. Stick to names that you are familiar with.
Unless you have a powerful computer start scans at 300 dpi or less if not you maybe waiting a long time for your computer to catch up to the scan or printing

Next time I will be discussing attachment briefly and installation. Following this with software, saving images and printing. Than we will get in to some practice projects for the scanner and you.

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