What are the specified performance criteria for densitometric reproducibility of base plus fog, mid-density, and density difference?

• A. Base + fog: +/-0.05; Mid-density: +/-0.10; Density difference: +/-0.10
• B. Base + fog: +/-0.10; Mid-density: +/-0.20; Density difference: +/-0.05
• C. Base + fog: +/-0.02; Mid-density: +/-0.05; Density difference: +/-0.05
• D. Base + fog: +/-0.15; Mid-density: +/-0.25; Density difference: +/-0.20

Answer: (A)

Reproducibility in densitometry means repeated density measurements under the same conditions stay essentially the same, so the readings are reliable indicators of exposure and processing. The three measurements you’re watching—base plus fog, mid-density, and density difference—each have specific tolerances because they affect how stable and meaningful the readings will be.

Base plus fog is the background density from the film itself, without any useful image information. Because any variation here shifts the entire density scale, it’s kept under the tightest control. A deviation within plus or minus 0.05 ensures the background level remains consistent across measurements.

Mid-density represents the central portion of the exposure’s tonal range. It’s more susceptible to small fluctuations from scanner response, processing, or film variability, so a slightly larger tolerance is allowed—plus or minus 0.10—while still keeping readings reproducible.

Density difference is the contrast between two regions. It also needs to stay tightly controlled to guarantee that small changes in the image aren’t mistaken for real differences in exposure. Matching the mid-density tolerance at plus or minus 0.10 helps ensure the measured contrast is reliable.

In short, the specified criteria require base plus fog to be very stable, while mid-density and density difference can tolerate a bit more variation, yet still remain within limits that ensure consistent, meaningful densitometry readings.