Influence of image file and white balance on photographic color assessment

How the color parameters obtained from digital photographs may be influenced by illumination, file format, and subject color is unclear.

The purpose of this in vitro study was to evaluate color differences (ΔE₀₀) and CIELab color coordinates among different types of file formats of dental shade tab images with and without white balance.

Different shade tab colors (n=10) were photographed with a digital camera under standard conditions. The photographs were stored in RAW, JPEG, and TIFF file formats and evaluated with and without white balance (WB) adjustment by using an image software program and a gray reference card with known color coordinates. CIEDE2000 color differences between each image file format and the control group (RAW WB) were calculated, and interpreted by the visual perceptibility (PT₀₀=0.8) and acceptability (AT₀₀=1.8) thresholds. The ΔE₀₀ color shift was defined according to CIEDE2000 lightness, chroma, and hue and interpreted by the following respective visual acceptability thresholds: 2.92, 2.52, and 1.90. The differences among the color coordinates were analyzed by Kruskal-Wallis and Bonferroni post hoc tests (α=.05).

The color coordinates presented statistically significant differences between the file formats and control group (P<.001). Excellent matches (ΔE₀₀ ≤0.8) were observed on TIFF and JPEG saved from RAW-WB. Images without WB presented unacceptable mismatches (ΔE₀₀ >5.4). ΔE₀₀ color shift of images without WB were predominantly influenced by ΔH₀₀, while JPEG, WB, and TIFF WB were mostly influenced by ΔC₀₀.

Only compressed JPEG or TIFF files of dental shade tabs derived from original RAW WB photographs were able to achieve color differences within the limits of the 50:50% perceptibility threshold, providing excellent color matches with the RAW WB files.