Scanners are often rated by this attribute. The ratings quoted by the manufacturers, however, are more or less arbitrary. They indicate the maximum pixel density you have in the final output, but not necessarily how fine a detail in the original image the scanner can resolve. The two Visioneer entries lagged behind the field in resolving power. The color registration test measures the accuracy of the alignment of the CCD array's red, green, and blue planes.
Proper alignment is necessary to produce clean edges between colors.
The results, presented in pixels, describe the maximum distance between any two misaligned planes. Most scanners in the roundup performed adequately, except for Canon's CanoScan FB1200S and Pcafic Images ScanAce 1236U, both of which produced mis-registration over a full pixel. The color registration problem you see here may become more pronounced when you try to enlarge the image. The uniformity rating is derived by dividing the highest brightness level by the lowest. An ideally uniform scanner would achieve the uniformity rating of 1.