Optical Density Evaluation of Scanners
The NSTL (National Software Testing Laboratory) is the leading independent information technology testing organization for the computer industry, and conducts objective test to assess new and existing products for compatibility, performance, comparative performance, usability and functionality. Epson America, Inc. contracted with NSTL to evaluate the Optical Density (OD) of its photo scanners, and to benchmark the results with those from other manufacturers. NSTL followed the methodology described in ISO 21550, an internationally recognized standard that specifies methods for measuring the ability of scanner to capture tones especially in the dark areas of the original. The detailed results of their findings can be viewed here.
The overall results of NSTL's tests show that the Epson scanners outperform each of the tested competitors and provided the highest optical density. The test results also reveal the Epson scanners as having more consistent OD values over the test scans (i.e. for each test iteration). NSTL observed in its series of tests that highest OD value for HP scanners was 3.1, compared to the >4.0 value measured for the Epson 4490 Photo, Epson 4990 Photo and Epson V700 Photo. Amongst the Canon scanners, the maximum OD for CanoScan 9950F was close to 3.0 but the maximum OD for CanoScan 4200F and CanoScan 8400F were found to be less than 3.0. The maximum OD for the Microtek scanners, ScanMaker i900 and ScanMaker 9800XL were also observed to be less than 3.0.
Test Methodology and Results
NSTL followed the methodology described in ISO 21550 using Adobe Photoshop CS2 and a Stouffer T4110, (41 Step Transmission Guide 1" x 9") test chart. A Microsoft Excel spreadsheet was created implementing the formulas in ISO 21550 to populate the data and calculate the Optical Density. The test methodology involved 3 phases:
- Scan Images
- Process Images
- Populate the Excel spreadsheet for computing OD
Test results for all models tested are summarized in the chart below. To access the complete analysis results for each individual model, please click here.
| Scanner | Optical Resolution | Maximum Optical Density |
|---|---|---|
| Epson Perfection 3490 Photo | 3200 | 3.2 |
| Epson Perfection 4490 Photo | 4800 | More than 4.0 |
| Epson Perfection 4990 Photo | 4800 | More than 4.0 |
| Epson Perfection V700 Photo | 6400/4800 | More than 4.0 |
| Canon CanoScan 4200F | 3200 | Less than 3.0 |
| Canon CanoScan 8400F | 3200 | Less than 3.0 |
| Canon CanoScan 9950F | 4800 | Less than 3.0 |
| HP ScanJet 4370 | 3600 | Less than 3.0 |
| HP ScanJet 4850 | 4800 | 3.1 |
| HP ScanJet 4890 | 4800 | Less than 3.0 |
| MicroTek ScanMaker i900 | 3200 | Less than 3.0 |
| MicroTek ScanMaker 9800 XL | 1600 | Less than 3.0 |