Computer imaging concepts 6.

Scanners

Use scanner for multiple functions.
 Scanning may go to fax, copy, store documents, use optical character recognition (OCR) software or create e-mail attachments. 

-Scanners are cheap, but there is some question about the accuracy of the information provided about the scanner's output.
-The specifications most often quoted for scanners dpi (resolution) and bits per pixel (bpp)-- bit depth -are not  always applied in a standard manner.   Actual resolution and bit depth are usually lower than scanner manufacturers claim. Many so-called 48-bit scanners really deliver only 24-bits of useful information. That's enough for most users.

A flatbed or film scanner.

• Flatbed scanners are good for scanning pages from photos, books and magazines. The scanners at 2400-4800 dpi may be used for slide and film scans.  The higher resolution is needed to compensate for the small size of the originals.   To scan a 35mm slide, x-rays or negatives best to use a 35mm film scanner.
   
• A scanner's bit depth indicates how many bits it uses to define the color of each dot of an image.  The dynamic range of a scanner depends upon the sensitivity of its CCD and the capacity of its analog-to-digital converter (ADC).  A 24-bit scanner is the most commonly used.
   
• 36-bit and 48-bit scanners can recognize over 1 billion colors (question accuracy) . 
   
• Today, most applications default to the original size of the photo when you scan it. When you scan a 4- by 6-inch photo, it shows up as a 4- by 6-inch image in your application.

• Most imaging applications come bundled with the scanner allow the adjustment of such things as brightness, contrast, and color levels. 

• Experiment with different resolution and color settings for scanner-printer-screen combination to determine optimal settings.

Sensor type	CCD
Optical resolution	2,400x2,400dpi (minimum 600)	-Hp 5500c scanjet
Minimum bit depth (grayscale)	12-bit for film; otherwise 8-bit
Minimum bit depth (color)	24-bit for graphics and prints; true 48-bit for film
Maximum color depth scanned	48 bits
Transparency, slide, and negative scanning	Dedicated film scanner or flatbed with transparency adapter built into the lid or included as an accessory

Difference between optical and interpolated resolution.
Optical resolution is what the scanner can see. Interpolated resolution is what it can guess at. Ignore interpolated resolution when making a purchase decision.

Optical resolution is usually given as two number"600x1,200dpi."
-The first number describes the scanner's optical resolution-- the density of the coupled device (CCD) sensor or complementary metallic oxide semiconductor sensors (CMOS) array.
-The second number is the vertical resolution.
-For most applications, a 300 dpi scanner is adequate, although most inexpensive scanners offer 600dpi or better. For color graphics and photos, you will generally need resolutions of 1,200dpi or more.

File Size, Bit-depth and Resolution.
  The advantage of a bigger bit depth such as, 36-bit depth, are useful if you scan transparencies, slides, or negatives.  

If you plan to save an image for printing, format so that you can print at the highest possible quality on your printer.

Be sure to evaluate the software package when you're researching your scanner purchase.

Scan your images directly into software like Photoshop (Elements) or Corel Paint. 

Use	Scan resolution	Format
On-screen (Web, e-mail, fax)	72 to 300 dpi, 8-24 bit	GIF-JPEG (small files)
Optical character recognition (OCR)*	300 dpi, 8bit	TIF
Print small photo.	600 dpi, 24bit	TIF (uncompressed)
Enlarge or print large photo. Slides using flatbed	Use maximum resolution, 48 bit.	TIF (uncompressed)

*Keep in mind that most OCR packages can't accept data denser than 400 dpi, so increasing the resolutions beyond that doesn't help.                                

This information obtained from http://www.zdnet.com/products/stories/reviews/0,4161,2764059,00.html        

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