###### Abstract  
Image-assisted digital shade guides are increasingly popular for shade matching; however, research on their accuracy remains limited. This study aimed to compare the accuracy and reliability of color coordination in image-assisted digital shade guides constructed using calibrated images of their shade tabs captured by a mirrorless camera (Canon, Tokyo, Japan) (MC-DSG) and a smartphone camera (Samsung, Seoul, Korea) (SC-DSG), using a spectrophotometer as the reference standard. Twenty-nine VITA Linearguide 3D-Master shade tabs were photographed under controlled settings with both cameras equipped with cross-polarizing filters. Images were calibrated using Adobe Photoshop (Adobe Inc., San Jose, CA, USA). The L* (lightness), a* (red-green chromaticity), and b* (yellow-blue chromaticity) values, which represent the color attributes in the CIELAB color space, were computed at the middle third of each shade tabs using Adobe Photoshop. Specifically, L* indicates the brightness of a color (ranging from black [0] to white [100]), a* denotes the position between red (+a*) and green (-a*), and b* represents the position between yellow (+b*) and blue (-b*). These values were used to quantify tooth shade and compare them to reference measurements obtained from a spectrophotometer (VITA Easyshade V, VITA Zahnfabrik, Bad Sackingen, Germany). Mean color differences (\(\Delta\)E\({}_{00}\)) between MC-DSG and SC-DSG, relative to the spectrophotometer, were compared using a independent \(t\)-test. The \(\Delta\)E\({}_{00}\) values were also evaluated against perceptibility (PT = 0.8) and acceptability (AT = 1.8) thresholds. Reliability was evaluated using intraclass correlation coefficients (ICC), and group differences were analyzed via one-way ANOVA and Bonferroni post hoc tests (\(\alpha\) = 0.05). SC-DSG showed significantly lower \(\Delta\)E\({}_{00}\) deviations than MC-DSG (\(p\) < 0.001), falling within acceptable clinical AT. The L* values from MC-DSG were significantly higher than SC-DSG (\(p\) = 0.024). All methods showed excellent reliability (ICC > 0.9). The findings support the potential of smartphone image-assisted digital shade guides for accurate and reliable tooth shade assessment. 1 Department of Restorative Dentistry, Faculty of Dentistry, The National University of Malaysia, Jalan Raja Abdul Aziz, Kuala Lumpur 50300, Malaysia; [EMAIL_ADDRESS] (S.T.C. ); [EMAIL_ADDRESS] (S.Y.S. ); [EMAIL_ADDRESS] (M.Z.K.) Department of Research and Development, Tunka Abdul Rahman University of Management and Technology, Lorong Lembah Pernai.3, Pulau Pinang 11200, Malaysia; [EMAIL_ADDRESS] (S.T. mismatches in the conventional shade-matching method can arise from significant variations in natural tooth color and surface characteristics [2], as well as discrepancies in color perception among clinicians and technicians. Furthermore, factors such as the observer's age, experience, eye fatigue, color blindness, and lighting conditions [3; 4; 5], further contribute to the unreliable conventional shade matching outcomes [6], which results in greater patient dissatisfaction [3]. On the other hand, instrumental shade-matching devices, such as spectrophotometers and colorimeters, provide an objective approach to shade selection, addressing the limitations associated with the conventional shade selection method [6]. Among these instrumental shade-matching devices, spectrophotometers have been shown to offer more reliable measurements because of their ability to analyze light reflection across the entire visible spectrum [7]. However, spot measurement spectrophotometers such as VITA Easyshade V, with their small measurement window, can restrict the assessment of a natural tooth's overall color [8; 9]. In addition, spectrophotometers tend to be expensive and are not always readily available in clinical settings [9].