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Scanning Tips

Determining the Correct Amount of Resolution

  • More is not always better. Determine what your final application will be BEFORE you scan. In many cases a high resolution image will do nothing more but dramatically increase the file size, take up more disk space, and slow down the process.
  • Internet Applications: For e-mailing color photos or pasting images on websites, a resolution of 75 dpi is the best choice. The reason is the actual viewable resolution of the average monitor is 72 dpi.
  • Printing to Ink Jet Printers: Check your printer documentation for recommended printer resolution settings. We generally recommend ranges between 75-300 general. Only use a higher scanning resolution (301 dpi and above) for smaller images when detail must be captured in a small area because it will be enlarged later.
  • Laser and Commercial Printers: When printing an image to a laser printer or commercial printing press, it is important to understand the process in terms of line screen (a.k.a., LPI). Line screens are the number of screen lines per inch when an image is halftoned. Halftoning is the process of breaking the image down into a series of dots to reproduce continuous-tone art when printing on a press. A general rule when printing in one of these two manners is to scan one and a half to two-times the amount of the line screen. Laser printers that have resolution ranges of 300 and 600 dpi will have line screens between 50 and 100. Typical commercial printing is done at an average line screen of about 150. Therefore, an optimal scanning resolution would be from 225 to 300 dpi.

Scanning Tip: Monitor Gamma

Adjusting the monitor gamma is a critical step to ensure that you view your images properly. To adjust your monitor's gamma, please perform the following steps:

  • Choose the monitor gamma option by selecting SETUP under the file menu and clicking MONITOR.
  • Select the MONITOR GAMMA option.
  • Drag the slider bars until the hue inside each rectangle is the same color as their adjacent colors. When finished, click OK to exit. Note: The steps for adjusting your monitor gamma may vary dependent on the application.

 

For Additional Help

Under the HELP menu, click HELP. This directory lists complete information about all of your image-editing program's basic and advanced functions. Use it to guide you through any questions you may have.



Buying Scanner Tips

How to Buy a Scanner?

The first step in purchasing a scanner is to think in terms of what your needs are as well as your budget. Will you be purchasing a scanner primarily for e-mailing pictures and/or creating web sites? Or perhaps you are interested in a scanner that will allow you to perform various faxing or copying functions. Dependent on your needs, certain models may be more attractive based on their features and specifications. It is important to understand those features and specifications clearly to help you make the best purchasing decision.

How Much Resolution Do I Need?

The resolution specification is the first specification that most people are interested in, however it is also one of the most misunderstood specifications. Resolution is expressed in terms of dots-per-inch (dpi) and determines the overall detail of an image. There are other terms such as optical resolution and interpolated resolution that should be addressed.

Optical resolution can be thought of as the scanner's "true" resolution. This figure is determined by the amount of scanning pixels on the scanner's CCD (the light sensor that captures the image) divided by the scanning area of the image. For example, a CCD that contains approximately 2,550 pixels divided by the horizontal scanning area of a typical scanner (8.5"), equals 300 dpi.

Interpolated resolution is added resolution that is created by the software of the scanner itself. Basically, a 300 dpi image can be further broken apart as additional dots are added. These additional dots take the averages of the nearest pixels to selectively determine the proper color values. Interpolation can have a softening or smoothing effect, but will also increase the physical file size of the image dramatically.

When shopping for a scanner, the important figure is the scanner's optical resolution. Another issue of course is to understand how much resolution to use for each application. Many people will automatically assume that they need to always use the highest amount of resolution available for the best quality. This is not true. When scanning an image with a defect or flaw, the added resolution will only pronounce this flaw.

Resolution and file sizes of images are directly related. As you increase the scanner's resolution, the file size will also increase. For e-mailing an image or placing it on a website, it is important to not use too high of a resolution. The average viewable resolution on a typical monitor is 75 dpi, so it is unnecessary to scan at any greater dpi when displaying items on screen.

For printing to ink jets or color laser printers, you need not go beyond 300 dpi as the printer's available line screen figure (the amount of lines per inch available when an image is halftoned) will typically never move beyond 100 lpi. Halftoning and line screen are advanced concepts that are important to know and understand when printing at a commercial printing house, but are usually not significant for home. The rule of thumb is to scan an image at one and a half to two times the available line screen of your output device. Following this rule, you can see that 300 dpi is adequate.

So what is higher resolution such as 600 dpi used for? High resolution should only be used when scanning small images that you later want to increase in size in order to retain detail.

The Bit Depth Specification

The second significant specification that is examined is the bit depth figure. Scanners have progressed through various stages including 24-bit, 30-bit and now 36-bit. We typically think that the higher bit depth will provide greater value, however this is not true for everyone.

Mathematical formulas are used to determine how many colors a certain bit depth figure can capture. In theory, the numbers are impressive with 24-bit, 30-bit and 36-bit scanners each having the capability to capture 16.7 million, 1 billion, and 68 billion colors respectively.

There are other issues however that may lessen the importance of these figures. Some of the added bits in a scanner are used for alignment and filtering purposes to help clean up the signal so that in the end, the true colors captured are perhaps less than the numbers applied. Additionally, typical desktop computers are limited to viewing 24-bit images on screen due to the limitations of the video card and/or software.

In the end, the bit depth figure is more important for professional designers or those searching for the highest level of detail when printing commercially.

Bundled Software Package

.Virtually all scanners on the market feature software to edit images and recognize text (OCR). Some time spent studying the software packages and their features will help you determine if they offer the added value that you are searching for with a scanner.

It is natural that higher end scanners will include software that is also considered high end. Keep in mind that high end might not always mean best. Consider the learning curves involved with many of the software applications available. For those people who want to do simple color corrections, there are various software packages available that will do these things simply and easily.

What Other Scanning Features Should I Look for?

Some scanners offer versatile features such as the ability to use the device as a fax sending machine or as copy machine. Other scanners allow you to scan slides and negatives as well as general documents and images. Some models also provide a parallel port interface that offers an easy, hassle-free installation as well as offering the ability to use the scanner with most portable notebook computers.

Some of these features, such as an included transparency adapter to scan slides and negatives may cost a bit more. For some, the added functionality of the scanner is worth it, for others not. Only you can truly determine what features you need the most.

Are you looking for a basic scanner for home use and simple projects? A 30-bit 300 dpi, parallel port model would probably be the best choice. Perhaps you are searching for a scanner that will serve as an office companion. Features such as the ability to scan legal size or larger may be an issue. You would also probably want the ability to fax or copy. Perhaps you are a graphic designer that needs many of the features a 36-bit scanner can offer. A model that not only offers 36-bit color depth and 600 dpi resolution, but includes a transparency adapter might be the ideal choice.



Technical Tips

Scanner Image Sensors CCD and CIS

There are two primary image-capturing sensors used in flatbed and sheetfed scanners: the Charge Couple Device (CCD) and the Contact Image Sensor (CIS). The table below details some of their basic differences. The following table is a description as well as a comparison between the two image sensor type.

CCD
CIS
Signal to Noise Ratio
Good
Poor
Focal Length (distance between sensor and image scanned)

Deep (Variable)

Shallow (0 3mm)
Power Consumption
High
Low
Data Rate
Fast (Averages 15 MHz)
Slow (1 MHz)
Mechanical Layout
Difficult
Easy
Component Size
Large
Small
Image Quality
Good
Poor
Suited For
Flatbed and moderately sized sheetfed scanners
Sheetfed scanners
Depth of Field
Deep (Variable)
Shallow (+/- 0.5mm)

 

24-bit vs. 30-bit Scanning What are the differences?

The promoted difference: 16.7 million vs. over 1 billion colors

Scanner companies state it clearly: a 24-bit color scanner can capture 16.7 million colors. At 30-bits, the number of colors captured is more than 1 billion. It takes no magic determining the figures; all that is used is a simple mathematical formula. The 30-bit scanner's ability to scan from a larger palette of colors results in a more accurate representation of the original image.

The hardware difference: 8-bit A/D converters vs. 10-bit A/D converters

Clear distinctions between 24 and 30-bit scanners can be made by examining their internal hardware. A 30-bit scanner uses a 10-bit A/D (Analog to Digital) converter; the same used within digital televisions and PC video boards. The A/D converter itself can be thought of as a type of signal translator. The A/D converter converts the input signal (i.e. the item scanned) into a digital form of 0's and 1's. The larger the bit type of the converter, the more information it can translate. The converter used then is critical in defining the final quality of the scanned image.

A 10-bit A/D converter within a 30-bit scanner converts each primary color individually; 10-bit red, 10-bit blue, and 10-bit green, all totaling 30-bits of color depth. 24-bit units use an 8-bit A/D converter that works on the same principal. Each red, green, and blue color receives 8-bits of conversion totaling 24-bits.

Some companies entering the market may claim to have 30-bit technology within their scanners, but to truly be a 30-bit scanner, the10-bit A/D converter must be present. The more costly 10-bit A/D converter must also be used with a more advanced set of circuitry. There are no software enhancements that can be substituted to give 30-bit color depth performance.

At a glance…The 24-bit vs. 30-bit histogram

Histograms can display the differences between 24-bit and 30-bit color detail. In the following histograms, each vertical line represents an individual scanned tone of color. The smooth transitions of color with a 30-bit scan can clearly be seen in Figure A. Figure B's histogram reflects some difficulty with capturing the image. The coarse lines indicate gaps within the color spectrum.

Figure A.
30-bit scan after 24-bit software conversion
Figure B.
24-bit scan after 24-bit software conversion


Figure C is a picture of the original photo used for the histogram comparison. Both 24 and 30-bit scans were made at 300dpi resolution using the factory default color/tone settings.

30-bit opponents

Makers of 24-bit scanners counter the merits of 30-bit technology by stating that since 30-bit scans must be converted to a computer's 24-bit application software, the color palette is ultimately limited to the number 24-bits can produce. Therefore, it is argued, any scanner beyond a 24-bit is useless with today's software support.

Theoretically, this sounds like a logical statement. However, since a 30-bit scanner has a larger palette of colors to choose from, the conversion to 24-bit allows only the strongest, clearest pixels to be selected. Electronic noise, i.e. signal degradation from the scanner's various components, are also filtered out with a 30-bit scanner's extra bits. The histogram clearly shows the effect of 30-bit color scanning after the 24-bit conversion takes place.

The future trend

Retail prices for consumer flatbed scanners are on a continuing downward slope. The price gap between 24 and 30-bit scanners in particular has shortened. As a result, by year's end, 30-bit scanning technology will become the entry-level standard in SOHO and home markets.

30-bit scanners offer the advantage of capturing a larger palette of colors that result in more accurate scans. By using the latest hardware technology, 30-bit scanners provide superior performance over their 24-bit counterparts.




Pixel-by-Pixel Technology

High-end color alignment technology moves into consumer grade scanners

One of the factors that separated high-end scanners from their lower end counterparts was the scanner's ability to properly align colors. A scanner with poorly aligned colors will produce an image that appears blurred. "Pixel by Pixel" is a technology that is similar to the technology found in professional-grade flatbed and drum scanners and will make its way into consumer-level scanners this year. Pixel by Pixel's significance is that it will finally dramatically reduce the poor color alignment and overlapping problems caused by the current "Line by Line" scanning system.


How "Line by Line" Works

When an image is scanned, the information is first captured by the CCD's (Charge Couple Device) photo sensors. In the current Line by Line system, the CCD captures the red, green, and blue information simultaneously, but the final processing of these colors is done separately before being sent to the software.

Unfortunately, misalignments of color occur because the scanner's motor is in continual motion and must rely on a timing system that does not allow perfect synchronization. This color misalignment problem could only theoretically be corrected if the scanner's motor were to physically stop completely before each line is scanned. The result of a Line by Line color misalignment can be seen when zooming in on an image or portion of a text document scanned in a color mode (see Figure A below).

How "Pixel by Pixel" Works

Pixel by Pixel technology is different from Line by Line because it takes the CCD's information and then processes all three color channels simultaneously. Because of this, there is little misalignment problems inherent with a scanner using Pixel by Pixel technology. Colors are sharp and the image itself appears more properly focused.

Keep in mind that Pixel by Pixel and Line by Line technologies have nothing to do with single-pass or three-pass technology. These other technologies refer to the number of times the image must pass over the CCD before they are processed. Pixel by Pixel and Line by Line refer to the actual processing stage itself.

Testing a Scanner for Pixel by Pixel Capability

Pixel by Pixel technology is not marketing hype. Indeed, the results of Pixel by Pixel scans are very clearly seen, even by typical non-professional scanner users. To determine if a particular scanner uses Pixel by Pixel technology, scan a page of black text in RGB color mode. After scanning the image, zoom in to the edges of the text and magnify it. If you can see small bits of green, red, blue, or other colors, then this is a scanner that uses a Line by Line system (see Figure A.). A scanner using a Pixel by Pixel system (see Figure B.) will show little or no extra colors, even under very heavy magnification.



Figure A. A line by line scanner showing the typical misaligned red, green and blue color values (character scanned in color, 300 dpi, magnified 350%)


Figure B. A scan created with Pixel by Pixel technology shows accurate color alignment (text scanned in color, 300 dpi, magnified 350%)