By Howie Fenton
If you go shopping for a scanner you will be inundated by specifications which look like a bowl of alphabet soup. You will see terms such as dpi, lpi, CCD, PMT, TWAIN, and SCSI. As if the alphabet soup was not confusing enough there are other issues such as actual vs. interpolated resolution, plug-ins vs. dedicated software, and 8 vs. 10 bit depth scanning. This article will help you decipher the alphabet soup and understand the issues in buying a desktop scanner or high end scans.
As a reader of this magazine and a customer of service bureaus you are most likely are not going to buy a $100,000 drum using PMT (photomultiplier tube) technology because of cost or $200 hand-held scanner due to quality. Most likely you will buy something in between, such as a desktop scanner using CCD technology. Even if you buy a CCD scanner there may be times when you need to buy a scan from a high end scanner and we will discuss why.
Desktop scanners or CCD (Charged Coupled Device technology) scanners measure the light reflected off or through the transmitted from the original. They use one of two light sources: bright white light with RGB (red, green, blue) filters or RGB lights. The CCD typically uses reflective light that bounces off the image and thought the lens into the CCD scan head.
The CCD scan head converts the different light intensities to varying voltages, which are sent to the analog to digital converter. Different voltages are converted into 1's and 0's which the computer uses to produce the different shades. This is how the light stimulates the imbedded arrays of CCD's (light sensitive devices) and generates an analog signal for A/D (analog to digital) conversion.
Resolution can be a confusing factor, because of the "rule of thumb" input to output ratio and the true resolution verses interpolated resolution issue. The more diodes in the CCD array the more information captured. But the "rule of thumb" for scanning is that you need twice as much input resolution or dpi (dots per inch) for the corresponding output, printing press, lpi (lines per inch). In other words you only need 300 dpi for a printing press utilizing 150 lpi screening.
Higher resolutions are only necessary when scaling up or blowing up images. For example, you would have to scan a slide at 2000 dpi if you used it at 8" x 8" for 133 lpi screening. Why? A 35 mm slide is about 1' x 1' in size. If scanned at 2000 dpi at the 1' x 1' size, blowing it up to 2' x 2' would result in 1000 dpi, scaling it to 4' x 4' results in 500 dpi and a 8' x 8' final size would result in 250 dpi. And since printing at 133 lpi requires about 266 dpi, you would have enough information.
Looking at input resolution can be misleading too, because there is true resolution and interpolated resolution and most companies quote interpolated. Most flatbed scanners today, costing less then $5000 capture between 400 - 600 dpi true resolution. True resolution is the actual or optical resolution captured. The CCD chip itself determines the true horizontal resolution while the stepper motor that moves the scan head dictates the true vertical resolution.
To create interpolated resolution software looks at two adjacent pixels in the image and averages them to create an intermediate value. Generally, an interpolated scan of a picture (halftone) is not as sharp as the real thing. However interpolation is useful for linework scans because it can smooth the jagged edges on curves and diagonal lines.
Another issue is how many bits are captured and how many are used. Most color flatbed scanners capture 8 bits of information per color (pixel) for a total of 24 bits or 16.7 million. Most experts agree that eight bits per color is enough to produce good-quality output. But 8 is not enough.
Strange as it sounds an 8 bit scanner does not capture 8 bits of information. Because of what has been come to be known as 'noise' or 'check bits' each 8 bit scan loses about 2 bits resulting in 6 bits per color which is a significant loss. In addition, capturing more than eight bits also makes a scanner's auto-exposure feature work better.
When using an eight-bit scanner, the auto-exposure feature sets just the brightness and contrast to determine the minimum black and maximum white points in the scan. However, a third point known as the midrange threshold point, or cutoff point also significantly affects how an image will look. This point determines how the scanner interprets various intermediate voltage levels. When using the auto-exposure feature with scans from an 8 bit scanner no midrange value is calculated.
Using the auto-exposure feature with scans with more the an 8 bit depth allows the software to create an intermediate value. The result is a resulting image with better shadow and highlight detail.
Dynamic range refers to the scanners' ability to capture an images' gradation from the lightest highlight to the darkest shadow. Theoretically the best dynamic range would be a straight line on a graph on which charted the original density against reproduction density. Most scanners however, will loss data in the high or low ranges. This loss of data results in a curve often called the 'gamma curve,' 'density curve' or 'gradation curve'.
High end drum scanners typically have a greater dynamic range then CCD scanners. Of course, the amount of information lost or the resulting quality is meaningless if the scan does the job. Therefore, one of the things to consider throughout this article is does the scanner or scan achieve your goal.
If you are publishing newsletters, trade journals, journals, etc. CCD scanners may allow you to bring the entire process in-house. Occasionally you may need to see the shine of her lips or the twinkle in his eye and to achieve that you may need to buy scans from a high end scanner.
Looking at bit depth alone, or resolution alone does not tell the entire story. The other half of the battle is to eliminate the 'right' data or the data which will minimize the loss in the resulting picture.
The dynamic range of the picture is wider than that of printed output, so any eight bits of data is not right it must be the best 8 bits. The trick is to capture the best eight bits from the original to produce the least compromised printed piece. The best software gives the user the ability to selectively eliminate the data which will minimize the loss in the final printed piece.
Many scanners come bundled with as Adobe Photoshop. This is great if you don't already own Photoshop but if you already own it you should look for a good scanner software driver. Features in software drivers can result in tremendous differences in workflow and productivity. For example, software that allows you input final size and resolution and calculates the scanning resolution automatically can save you from hours of calculating output size and resolution.
Plug-ins or extensions into photoretouching or page layout programs can help save time and reduce the total memory required. If your scanner doesn't offer plug-ins then you have to capture the image in the scanning software first and save it. If you have enough memory you can simply leave your scanning software running and open your photoretouching program such as Photoshop.
Keep in mind that both scanning software and photoretouching software typically require a minimum of 4 Mb of RAM. Meaning you would need at least 8 Mbs and with system software 10-12 Mbs.
However, programs such as Photoshop works best when there is three times the size of the file allocated to the photoretouching program. In other words to work optimally on a 5 Mb file you should allocate 15 MB of RAM to Photoshop. In addition you may need 17 Mb for the scanning software and the operating system, meaning you would need 32 Mbs of RAM to work with the two programs efficiently. With plug-ins you can work within one program.
The solution that allows you to scan into a photoretouching program is something called TWAIN. According to Robin O'Leary the Senior Marketing Manager of Electronic Desktop Solutions at Agfa, Division of Miles Inc. TWAIN is a standardized "language" designed to open the desktop market to imaging by giving software applications direct access to image or raster data. It was conceived in early 1991 by a group of 5 companies as a response to market requests for an imaging standard. This group of five became known as the Working Group and included Aldus, Caere, Eastman Kodak, Hewlett Packard and Logitech. Other major contributors to the initial design included Adobe, Howtek and Software Architects.
Jokingly O'Leary says that TWAIN, stands for the Technology Without An Interesting Name. The TWAIN standard makes scanning much simpler, letting you capture images directly from within any TWAIN-compliant application. TWAIN is designed for applications operating on the Apple Macintosh (System 6.x and 7.x) and Microsoft Windows environment (Version 3.x).
For Macintosh applications TWAIN is implemented via plug-ins. On the PC there is a TWAIN driver. Some photoretouching programs, such as Micrografx's Picture Publisher, support TWAIN. All you have to do is click on the menu option entitled File Acquire. This opens a window that you can preview the image; select the area to be scanned; choose black and white, gray-scale, or color; fine-tune brightness and contrast; or just scan. When you're done, the image is placed into the photoretouching application.
If you load your scanning software onto your PC be warned you might be adding drivers to your CONFIG.SYS file. If that occurs RAM will be allocated to that driver even when you're not using the scanner. If you're a power user you might set up different CONFIG.SYS files for different purposes or figure out a way to skip the loading of unwanted drivers at start-up.
For Mac users most scanners simply plug into the existing SCSI (Small Computer Systems Interface) chain. Some however use self termination and therefore should be plugged into the end of the SCSI chain.
On the PC often the scanner will ship with an inexpensive 8-bit board. Although easy to install completing a PC scanner installation may require setting interrupts, DMA channels, and SCSI ID numbers
If you're concerned about available slots and would like the option of adding other devices to your SCSI chain call the manufacturer and ask if the scanner is 'true' standard SCSI or if it uses proprietary interface. If it's proprietary you're stuck. If not a true SCSI you can plug the into any fast 16-bit SCSI card such as Adaptec's, Western Digital's, or Future Domain's scanner and up to six other devices.
If there is a common denominator for the PC SCSI drivers it is called ASPI or Advanced SCSI Programming Interface. You can get ASPI drivers from the scanner maker, or you might consider a SCSI toolkit such as Corel Systems' CorelSCSI, which provides ASPI drivers for almost every device on the market.
The SCSI switch should be easy to use and easily accessible. Therefore the SCSI switch should be a push wheel or rotary wheel and not a set of DIP switches requiring theoretical physics or a manual to decipher.. In addition, it should be on the front or back of the scanner, you shouldn't have to left it up to reset it.
All this alphabet soup and talk about issues is important but equally important is taking the scanner for a test drive. After all you wouldn't buy a car based on a brochure alone. Before you buy a scanner run it through its paces and create a sample project.
Take examples of the pictures you would use to the dealer and have them scan it for you. Don't depend on their samples. They may use pictures that always scan and reproduce well.
When they scan it, time how long it takes to set-up the scanner, scan the images and retouch them. Also see if they can scan directly into a retouching program which would allow you to work with less RAM.
Ask lots of questions. What software comes with the scanner? If they tell you it comes with software such as Photoshop, find out if it is the full featured version or a 'Lite' version. Determine if it is the most recent version (e.g. 3.0) an older version (e.g. 2.51) and if an older version can it be upgraded inexpensively? Ask what doesn't come with the scanner which might make it more efficient. For example, does it come with color management software, calibration software, or scanner targets?
Talk to the dealer about your computer configuration. Ask them if you have enough memory, a fast enough computer, and all the software you need to complete the task. If you don't have everything you need, then you will have to add those costs to the cost of the scanner, to determine the final cost.
Once you have the scanned images, create your sample piece. If you are planning to use PageMaker and output to a color copier - do it. If use XPress and create four color film from a service bureau, then make a film based proof.
Examine the quality. If the quality does not match your expectations you may have to look at other scanners or consider buying a high end scan. For demanding work or a more thorough comparison you might buy a high quality scan and compare it to the results from your desktop scanner.
When you have your sample piece in hand, or a few sample pieces and all the costs calculated you will have all the information to make a good decision. Good luck and good scanning.
There are a host of good scanners available and more are being introduced everyday. Here are winners from a few recent magazines.
According to MacUser, Feb 1994 the best scanner they tested in the less then $2000 category was the La Cie Silverscanner II ($1,599 direct). They conclude that it comes with an excellent Photoshop plug-in that's filled with productivity-enhancing features and was among the top performers in their speed and image-quality tests.
According to PC-Computing, June 1994, HP's $1,179 ScanJet IIcx wins top rating in a comparison of 10 flatbed color scanners capable of reading 16 million colors at resolutions of 300 to 400 dpi. It received a score of 86.9 out of 100, and offered the highest image quality at a reasonable price. It includes well-designed scanning software, easy set-up procedures and a large 18-by-14-inch window.
According to MacUser, Nov 1994 the three best moderately priced scanners are : PixelCraft Pro Imager ($13,000), the Kodak RFS 2035 Plus slide scanner ($9,000) and the Leaf Leafscan 45 transparency ($17,000).
In awarding the PixelCraft Pro Imager four and half mice they say [It] 'Lets you get the best possible scans from a variety of images- whether weather beaten prints, large format originals such as paintings, or high quality photographs. The software is top-notch.'
In describing the Kodak RFS 2035 Plus the say it makes acquisition of mounted or unmounted slides nearly foolproof and fast. For high volume scanning of originals that need little correction, this slide scanner is hard to beat.
At the upper end of their $20,000 price category is the Leaf Leafscan 45 which was the only scanner tested that could capture 16 bits of data per color. They conclude that it provides excellent output quality, has good software but was a little slow.
At MacWorld Boston Agfa introduced a new Arcus scanner called the Arcus II. Arcus II is a 12 bit scanner with a scanning resolution of 600 dpi (horizontal) x 1200 dpi (vertical). Using software interpolation this results in 2400 dpi for halftones and 3600 dpi for lineart. It has a dynamic range of 3.0 and can scan 8.3' x 14' reflective originals and 8' x 10' transparencies. It comes bundled with FotoLook scanning software, FotoTune LE (Lite) Color Management and Adobe Photoshop 2.51.
The Arcus II came well packaged and included a handle to carry the box that enclosed it. After unpacking there are several separate manuals, one each for the scanner, FotoLook, FotoTune and Photoshop Lite. Similar to older Agfa scanners a few minutes are required to unlock the scanner after shipping. Compared to the Agfa Focus scanner which had several unlocking screws and elaborate manipulations (turning it one way and then another) the Arcus was much easier to unlock.
We installed the software onto a Mac II ci with a Radius Rocket accelerator. The scanning software loaded easily and installed drivers into Photoshop and XPress for easy scanning access. However, when we tried to use the software we ran into some problems.
We tried to preview scan both color and black and white originals using the FotoLook scanning software as well through the Photoshop and XPress plug-ins. Each attempt resulted in a screen freeze with a dialog box saying 'calibrating scanner."
After trying several options we found that we could scan if we used the option for 'optimum speed' as opposed to 'optimum quality." After scanning for 'optimum speed' we examined the software and found it quite impressive. It offers the ability to prescan, control white point/black point, Dmin /DMax, exposure control, tone curve, descreening and white/black point.
Unfortunately we ran into a problem that did not allow us to test the actual quality of the resulting scans. This may a general software bug or a problem unique to the equipment configuration we used. Agfa officials said they had experienced this problem with earlier versions of the software but not with the version we used.
However, we were impressed by the software and scanner spec.'s for the price. For a list cost of $3500 you get 12 bit scanner, good scanning software and 'lite' versions of color management software (FotoTune) and retouching software (Photoshop).
Considering the success of the original Arcus we believe this one is worth another look. If your looking for a moderately priced scanner we recommend taking your own original into a local dealer and watching over their shoulder as they scan it. That way you can see if the software is working in the 'quality' mode and you can determine if the output meets your needs.
FENTON ON PREPRESS INDEX