Flatbed Scanners - the Ultimate Guide

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The flatbed scanners are the most widespread type of scanners, thanks to their universality and huge choice of brands and prices. The flatbed scanners can be based on contact image censors (CIS) or charge coupled devices (CCD). In the first case optical censor is made as a ruler of photo cells on whole width of the scanner. Thus, disappears necessity for mirrors and lenses, and, as the result, strongly decreases cost of manufacturing. A downside of CIS-scanners is a poor color image scanning quality, therefore the CIS technology is usable only in the cheapest models (on the other side, CIS flatbed scanners can be very compact). CCD flatbeds use system of mirrors and lenses to focus image on the tiny CCD sensor.

The flatbed scanners can be divided into three categories:

SOHO (Small Office/Home Office) scanners (under $100 - $300)

The sphere of application is clear from the name. Usually, they have optical resolution 300x600 or 600x1200 dpi and color depth 30 - 36 bits. Almost half of the cost of such scanner could be the cost of optical censor, therefore proceeding from the price it is possible approximately determine quality of scanning (however, for the black-and-white documents it is absolutely unimportant). SOHO scanners priced about $300 usually bundled with the transparency adapter (for film scanning) and/or automatic document feeder (ADF). The transparency adapter is some kind of a fictitious accessory - device of such cost are not capable to produce even average quality output of slides and especially negatives (however, it may be enough for preview purposes or for newspaper). If there is the necessity to get an image from a negative, it is possible to scan a photo made from this negative, or to pass this task to a scanning bureau (so called repro center). When scanning documents, the most important factors are speed, availability and capacity of automatic document feeder (ADF), TWAIN compliance and quality of OCR software bundled with the scanner (OCR software alone may cost more than a scanner). TWAIN (Toolkit Without an Interesting Name) is a standard protocol for data exchange between scanner driver and third-party software (image editing, archiving, OCR, etc.).

Tips from MacGuru:

Specified double-numbered resolution like 600x1200 dpi means the following: first number - resolution of optical system, second number - resolution of stepping motor which moves scanning head. Obviously, only resolution of optical system does make a sense. So, scanners with passport optical resolution 600x600 dpi, 600x1200 dpi and 600x2400 dpi are essentially the same.
Forget once and forever about interpolated resolution if you count on quality. Sometimes, its possible to scan at 1200 dpi on the scanner with 600x1200 dpi resolution if software is good enough. Interpolation means that missing pixels will be generated using software. Remember, only software with fractal interpolation capable to achieve good quality of interpolated images and it costs several hundreds bucks.
Never pay attention to the high-number color depth specified by manufacturer - SOHO scanners use very cheap and use low-quality CCD, and thus, extra bits are nothing but noise. SOHO flatbeds with 24, 30, 36, 42 and 48 bit color depth are not different in terms of output image quality (good scanning software may have much more impact). True 48 bit flatbed could costs $15,000, but not $150..
Never scan printed images at resolution over 300 dpi - it is completely useless since even art prints made with 300 dpi graphic files.
Optical density range (see more detailed explanation below) of SOHO scanners is usually 2.8, if not specified by manufacturer otherwise. Thus, these devices produce images from transparent originals suitable for preview or newspaper print purposes only (see tests #N/PL11K/F-MVS, T/PL11K/G-ST).
If you scan prints "as is" (without any correction), you will notice that they are distorted with moire. You should use descreen filter which must be available with scanning software (do not buy a scanner if its software do not have such filter). Descreen filter requires certain lpi (lines per inch) value. Common pattern: newspaper - 85 lpi, magazine - 133 lpi, art print - 175 lpi. Remember to place original precisely horizontally, otherwise descreen filter will not work. See test #R/PL11K/P-DMR.
In many cases even very cheap CCD (not CIS) flatbeds (under $100) can produce acceptable color quality if their scanning software properly used. You should use feature called auto-density (name may change from "Auto" to "Super Colors" or something like this) which automatically sets necessary black and white point temperature, contrast and brightness values. However, scanning area should include only image itself, not white space areas and black frames around. Unfortunately, due to low-cost CCD sensors effect of using auto-density often is not so obvious.
Do not forget to use USM (unsharp mask)! Effect of using USM may be seen in the test #T/PL11K/FR-USM.
If you intend to scan a lot of color images, check if scanning software has real-time preview of color settings, batch scanning (capturing multiple images with the same color adjustment settings) and multiple scanning (capturing multiple images with different color adjustment settings) modes. If not, just do not buy it.
Sometimes software bundled with midrange flatbeds can be used with SOHO scanners of the same manufacturers and is available as free download. For example, UMAX MagicScan works with some Astra models.

Scan Tests

All images have been re-sampled for Web publishing to 72 dpi (from 300 and 1200 dpi), resulting some loss of details and sharpness. Thus, some tests may become not so obvious when viewed within Web browser.
Binuscan do not allow to turn off sharpening and auto-density. So when compare scan results please take this into account, because in most cases other software have been used with sharpening off.
Posted test images are quite big, so it will take some time to download them, especially if you have dial-up modem connection.

Test Images
Mat photo (ice-cream)	Glossy photo (toys)	Art Print (175 lpi)	Slide, gold tones (battle)

Slide (food)	Slide, skin tones (girl)	Negative (food)	Slide (fruits)

Hardware: UMAX Astra MX3 (under $100), UMAX Astra 4000 (over $200).

Software: UMAX MagicScan 4, Binuscan 4.

Test Samples/Software Settings: 300 dpi for reflective, 1200 dpi for transmissive originals; RGB mode (otherwise noted); auto-density on (otherwise noted); color cast removal on (for negatives only); all extra filters off (otherwise noted), except Binuscan which do not allows to turn off sharpening and auto-density; all other special setting mentioned separately in the test pages.

Test #	Description
R/AMX3-4K/IC	Reflective scan (ice-cream), Astra MX3 and Astra 4000 with default UMAX software and Binuscan
R/AMX3-4K/T	Reflective scan (toys), Astra MX3 and Astra 4000 with default UMAX software and Binuscan
R/AMX3/IC-D	Reflective scan (ice-cream), Astra MX3, auto-density test
R/AMX3/T-D	Reflective scan (toys), Astra MX3, auto-density test
T/A4K/G-ST	Transmissive skin tones scan, large slide (girl), Astra 4000, MagicScan and Binuscan
T/A4K/F	Transmissive scan, large slide (food), Astra 4000, MagicScan and Binuscan
N/A4K/F	Negative scan (with color cast removal), small negative (food), Astra 4000, MagicScan and Binuscan

Midrange flatbed scanners ($500 - $7000)

These devices (also often called semiprofessional) differ from their office counterparts by much better scanning quality (color accuracy) of both transparent and reflective originals. However, they are slower and are not intended for document scanning. Typically they have optical resolution from 1200 to 3000 dpi, color depth 36 - 42 bit and optical density range 3.3 - 3.6. The last parameter is extremely important for scanning transparent originals.

Speaking by the language of popular science, optical density range determines difference between lightest and darkest colors which optical sensor is capable to recognize.

Please note that optical density scale is logarithmic, not linear, so the difference between scanners with OD 3.0 and 3.3 is 30%, not 10%. Among with more sensitive and less noisy optic censors and more precision mechanics, midrange flatbed scanners often utilize other technologies in order to improve color accuracy:

Built-in color calibration. Before each scan, built in calibration strip is scanned and effect of heating and aging of scanner's parts like lamps and CCD greatly reduced.
Some scanners uses transparency tray which is installed between lamp and scanning head instead of transparency adapter, thus eliminating extra glass plate and possible Newton rings.
Multiple lens system allows to achieve higher resolution when scanning smaller areas. Scanner automatically switches lenses depending on requested resolution and size of original.
Movable scanning bad with fixed scanning head and lamp mounted on massive chassis is a solution pioneered by UMAX with PowerLook 3000. This approach allowed to decrease extra distortions due to vibration of heavy, complex and sensitive optic system (with scanning resolution 3000 dpi displacement total of 0.008 mm will result in distortion of the information).

Tips from MacGuru:

Due to price ceiling, limited market and tough competition midrange flatbeds manufactured with average quality parts. It may sounds fantastic, but scanning software may determine up to 50% of output image quality (in some cases it is impossible to get anything usable with cheap software). The truth is that due to cost savings bundled scanning software could be somewhat limited in terms of color adjustments and correction. My personal experience revealed that very good results could be achieved with Binuscan and LaserSoft Silverfast (both packages use completely different approaches for enhancing image quality), so prepare to spend extra few hundreds bucks over "standard package" for capable software (see test #N/A4K/F).
It is a good idea to choose a scanner which is bundled with calibration targets (even if this will cost extra). Calibration using targets will considerably improve output color accuracy, especially for cheaper models.
All scans made from negatives and not so infrequent from slides have certain color cast. Although some scanning software allow to set up film manufacturer whose mask characteristics are known, this not always work. Better to use intelligent software which automatically determines and removes color cast (see test #N/A4K/F). By the way, color cast can be removed manually with Photoshop .
In fact, there are only two types of high-quality scanning software for midrange flatbeds - first, most widely used (like SilverFast, ScanPrep Pro, LinoColor, etc.) offers a lot of adjustments with live preview plus few sets of default settings for certain image types (skin tones, gold tones, landscape, etc.); second completely works in autopilot mode (Binuscan) and use AI (artificial intelligence) and proprietary image quality enhancements algorithms in order to achieve good result. First suits more for color experts while second is very good for novices.
Scan completely black reflective original to check CCD noise and blooming. Gray and color dots appeared on the output image reveal low-quality CCD sensor.
Remember, all midrange flatbeds are very slow, especially at high resolution. They are designed for limited volume of scans.
If your scans made from transparent originals suffer from rainbow-colored lines (Newton rings), try to use anti-Newton spray.
If midrange flatbed does not satisfies you in terms of speed, output image quality and bundled software features you can consider secondhand professional scanner. Often it still carry limited 3-6 months manufacturer warranty. However, it should not be more than 1.5 years old (I meant not 1.5 years of use, but 1.5 years since end of production).
Why 24 bit color depth (its over 16 millions of colors) is not enough for high-quality scanning? Because that means only 256 levels of each component color (Red, Green, Blue).
Time to time (usually each 1.5 - 2 years) its a good idea to replace a lamp. Midrange flatbeds are not so smart to report too aging lamp.
Vertical black lines usually reveal dusty or dirty mirror.
Never pour water or other cleaning liquids on the scanning bad because it may damage calibration strip leading to expensive repair.

Scan Tests

Hardware: UMAX PowerLook III, UMAX PowerLook 1100 (actually PowerLook III mechanics and optic but FireWire interface), plus UMAX Astra 4000 (SOHO model) for comparison. First two scanners and the last one have the same optical resolution, but the 3x price difference.

Software: UMAX MagicScan 4, Binuscan 4, Silverfast 5.

Test #	Description
R/PL11K/P-DMR	Reflective scan (art print, 175 lpi), descreen (moire removal) test
R/PL11K/P-AD	Reflective scan (art print, 175 lpi), auto-density test
R/PL11K/T-AD	Reflective scan (ice-cream), auto-density test
R/PL11K/IC-AD	Reflective scan (toys), auto-density test
R/PL3K/IC	Reflective scan (ice-cream), MagicScan and Binuscan
R/PL3K/T	Reflective scan (toys), MagicScan and Binuscan
R/PL3K/IC-GR	Reflective grayscale scan (ice-cream), MagicScan and Binuscan
T/PL3K/B-GT	Transmissive gold tones scan, large slide (battle), Binuscan and SilverFast
T/PL11K/G-ST	Transmissive skin tones scan, large slide (girl), SilverFast (different modes), versus SOHO scanner
T/PL11K/FR-USM	What does USM (Unsharp Mask)
T/PL11K/FR-FBS-QE	Transmissive scan, large slide (fruits), few basic steps in order to enhance output image quality
N/PL11K/F-MVS	Transmissive scan, small negative (food), with color cast removal on, midrange versus SOHO
T/PL11K/FR-SVB	Transmissive scan, large slide (fruits), Silverfast versus Binuscan

Professional flatbed scanners ($14,000 - $75,000)

Such scanners are intended exclusively for the publishers of high-quality color prints and CD image libraries (with total number of scans reached thousands of originals in month), and bureau for custom-made scanning (repro-centers). The threshold in $14,000 is some kind of the standard - scanner cheaper $14,000 professionals will not consider as professional. Professional flatbeds are elephant-sized devices, weighting usually 80 - 100 kg (however, such weight allows to reduce vibration). If office scanners are similar against each other as twin brothers, professional scanners simply amaze with originality and variety of designs:

Multiple lens system (up to five) and movable scanning bad (like some midrange flatbeds).
Anti-blooming, low-noise and more sensitive CCD sensors result in much better scanning quality than midrange flatbeds, especially in highlights, shadows, and skin tones.
XY scanning with stitching (pioneered by CreoScitex) - scanning head moves in both directions in order to achieve full resolution over the entire A3-sized bad. This is essential for large volume production since tens of originals could be mounted and scanned at once.
Vertical align of optical system completely eliminates mirrors and makes optical path very simple (developed by Purup-Escofot/ScanView).
Electrostatic scanning bad allows to eliminate extra glass plate (used to keep originals flat) and time consuming preparations (pioneered by Imacon).
Dynamic thermoelectric cooling system which keeps CCD sensors within optimal temperature range (first used by CreoScitex, Supreme model).
Multiple sampling of each line of an image with producing average allows to achieve great color accuracy (first used by CreoScitex, Supreme model).
Adaptive light source(s) - use of different lamps or automatic light increase/decrease for different types of originals.

Professional flatbeds currently available from Agfa, CreoScitex, Fuji, Heidelberg, Imacon, Purup-Escofot/ScanView, Screen.

Tips from MacGuru (for novice shoppers):

When it comes to quality/price ratio (for positive transparent originals only), virtual drum scanners from Imacon are really good choice. As mentioned before, software which ships with Imacon scanners produce odd results with negatives. You can try to use LaserSoft Silverfast instead, but I have no responses how this combo works.
Many professional flatbed scanners with approximately the same resolution and optical density have huge difference in price. What's the matter? Speed. $14,000 flatbed is capable to produce 10 files/hour in average. Remember, these 10 files are high-quality and ready to use CMYK separated images, not just monster-sized files which require hours of hard work to be ready for final print. 1.5 speed increase usually costs around $10,000.
Ability of software to do something else while scanning process is active is essential for high-volume production (parallel workflow). Entry-level professional flatbeds usually do not support parallel workflow.
Check maximum thickness of reflective originals if you are intended to scan books and magazines. Additionally, some scanners cannot work with cover open.
If you feel that scanning screened film might be necessary, check availability of Copy Dot feature.
Never save on monitor for scanning workstation. It should be 21" or 22" professional model, very desirable with calibrator. Why not 17" or 19"? Due to the price war 17" and 19" real professional monitors just disappeared. I have very good feedback from people who uses monitors based on Mitsubishi Diamondtron NF aperture grille CRT. Mitsubishi's own Diamond Pro 2040u is really piece of art, it even equipped with GeoMacs system which compensates Earth magnetic field.
Drum or flatbed? Well, this discussion is somewhat religious and useless since professionals are conservative type of people who trust technology they used to use.
Never buy devices directly inherited from midrange flatbeds (like Heidelberg Circon, which is actually UMAX Mirage II with extra lens and more capable software).
Some professional flatbeds are not compatible with Windows PC at all. However, for device priced $15,000 or so few extra hundreds bucks for Apple Macintosh workstation does not mean anything. Additionally, MacOS built-in calibration system called ColorSync is mandatory for anyone who want to get precise colors on monitor and prints.
It is really hard to choose right model from wide variety of professional flatbeds due to differences in underlying technology, prices and brands. Better to use the following approach: if you have hired operator who is trained, for example, on ABC scanner, and certain ABC model satisfies you in terms of price, quality and speed, buy ABC.

Continued - a) Interface... , b) Binuscan Workflow...