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Today's scanners are versatile, lightweight, compact, and thanks to USB 2.0 and FireWire, faster than ever. But a scanner is only as good as the quality of the images it captures and the speed that it conducts those scans. At CNET Labs, we use a series of real-world tests to gauge the scanned image quality and the scanning speed of flatbed scanners. If applicable, we also test the quality of a scanner's film-negative and slide output.
| Test bed |
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For CNET Labs' scanner speed tests, we use a 1GHz, AMD Athlon-based Compaq Presario 5900Z running Windows XP Professional SP1, with 256MB of memory, a 9GB IBM Deskstar 8 hard drive, and a Matrox Millennium G450 graphics card. The system includes an integrated FireWire interface and a Maxtor USB 2.0 PCI card. Scanners are installed according to the manufacturers' instructions, connecting to either USB or FireWire. For those scanners that support both, we test using FireWire.
For our image-quality tests, scanned images are viewed on a 19-inch Samsung SyncMaster 957MB flat-screen CRT, connected to a 2.4GHz P4-based Compaq Evo W4000 running Windows XP Professional SP1, with 512MB of memory and a Matrox Millennium P750 graphics card.
| Speed tests |
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We time how long it takes to scan an 8.5x11-inch, one-page, color test document into Adobe Photoshop 6.0. The document is scanned at 150 dots per inch (dpi) using the scanner's default settings for a color document.
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We time how long it takes to scan Kodak Digital Science's Imaging Test Chart TL-5003 into Adobe Photoshop 6.0. The 8.5x11-inch document is scanned at 150dpi using the scanner's default settings for a grayscale document.
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We perform this test only with scanners that are designed to scan film negatives. We time how long it takes to convert a photographic negative into a digital picture using Photoshop 6.0.
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We perform this test only with scanners that are designed to scan film slides. We time how long it takes to convert a photographic slide into a digital picture using Photoshop 6.0.
For all speed tests, we start timing from the moment we give the command to scan to the instant the complete image appears in the Photoshop window. We perform three trials of each test and average the results for an overall score. The scores do not reflect scanner warm-up or TWAIN loading times. All scores are reported in seconds.
| Image-quality evaluation |
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We evaluate image quality for color and grayscale scans and, when applicable, for photographic-negative and slide scans. Our source color document is the same one we use for our color-photo speed test. The document was developed in-house at CNET Labs and is an 8.5x11-inch sheet that incorporates monochrome and color photographs, gradient patterns, continuous-tone color blocks, a multicolored overprinting test pattern, and detailed line-art graphics. For grayscale evaluation, we use the same material we use for our grayscale-document speed test, the Kodak Digital Science Imaging's TL-5003 chart; this chart contains 18 different test patterns, ranging from continuous-tone density blocks and reflection densities to a detailed grayscale photograph. We scan both documents at 150dpi and at the scanner's default settings for both color and grayscale.
A jury consisting of CNET Labs staff, editors, and the reviewers evaluate scan quality. We grade the color scan on the following criteria: color matching, color saturation, color gradient, geometry, exposure, noise, and focus. The grayscale scan is graded for overall image quality, focal clarity, contrast quality, and the presence or absence of artifacts, or chunks of stray pixels that don't belong in the image. Each 150dpi scan image is compared to images from previously tested scanners and assigned a rating of excellent, good, fair, or poor. The same process is also done with the scans of the photographic negatives and photographic slides when applicable.
