Technical Guide > Image Quality

Image Quality

There are many ways to create a digital reproduction of a work of art, and not all methods will produce an image of the same quality. We believe it is important for anyone intending to use these images to understand the method by which the image was created and what to expect from that image in terms of quality. In addition, images may be appropriate for one use but not another. Listed below are the most common digitization methods used at NGA and a short description of the expected quality to be achieved from each.

Direct Digital Capture
This is the highest quality digital reproduction produced at NGA. Artwork is captured using a professional, large-format, high-resolution digital camera back that is calibrated for color. The camera back’s multishot feature allows it to eliminate moiré interference patterns in the reproduction. The image is also corrected for uneven distribution of lighting, which results from lens falloff and nonuniform light distribution on the surface of the artwork. Each image is proofed against the original artwork under ISO1 proofing conditions and manually corrected when necessary.

Rapid Capture
Images are captured using a professional, medium-resolution digital SLR camera. The image is corrected for uneven distribution of lighting due to lens falloff. The camera is calibrated for color to assist in accurate reproduction, but each artwork is not reviewed individually for accuracy. Images are reviewed in batches, and batch color corrections are applied when necessary. This allows NGA to capture a high volume of images with reasonable accuracy.

Scanned E-6 Matched to Artwork
Before the National Gallery of Art created direct digital captures, all artwork was photographed on E-6 transparency film. These transparencies have been scanned using a professional flatbed scanner that is calibrated for color. However, because E-6 transparencies have inherent limitations with respect to accurate color reproduction, the scan is manually color corrected while viewing the original artwork under standard proofing conditions (or as close to standard conditions as the situation allows) to make the reproduction more accurate. An attempt is made to correct the most significant color errors, while less significant errors are allowed to remain. This allows NGA to produce acceptable reproductions from a scanned transparency in a reasonable amount of time.

Scanned E-6
The transparencies have been scanned using a professional flatbed scanner that is calibrated for color. The image has been color corrected (when necessary) to match the color of the transparency. The transparency may, or may not, accurately represent the original artwork.

Only images in the above categories are cleared for Open Access. These categories are identified for each image in the preview image metadata.

1 International Organization for Standardization