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| ORIGINAL ARTICLE |
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| Year : 2022 | Volume
: 18
| Issue : 4 | Page : 123-128 |
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The effect of camera and display technology on the reliability of digital shade evaluation
Aswini Kumar1, Venkitachalam Ramanarayanan2, D Harikrishnan3, Rahul Sajeev1, Athira Rejithan1, Vineetha Karuveettil2, Reshma Suresh4
1 Department of Prosthodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
2 Department of Public Health Dentistry, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
3 Department of Visual Media and Communication, Amrita School of Arts and Science, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
4 Department of Periodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
| Date of Submission | 16-Jul-2022 |
| Date of Acceptance | 02-Nov-2022 |
| Date of Web Publication | 20-Feb-2023 |
Correspondence Address:
Dr. Aswini Kumar
Department of Prosthodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, AIMS, Ponekkara PO, Kochi, Kerala
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/AMJM.AMJM_26_22
Introduction: For a successful prosthodontic rehabilitation, accurate and economic shade selection methods are warranted. Shade selection with digital cameras and various commonly used digital displays can be suggested as an alternative to expensive colorimetric instruments and inaccurate visual shade selection. To digitalize prosthetic rehabilitation, standards need to be set on minimum digital specifications required to capture and communicate accurate shade selection. This study aimed to establish a minimum specification required for a digital image, to achieve the most accurate result in prosthodontic shade selection, using digital photography. Materials and Methods: A cross-sectional study was conducted among 100 dental professionals with normal color vision. Sixteen shade tabs were randomly selected from two commonly used shade guides and were photographed using four different commonly used digital cameras under standardized settings. After dividing the shade tabs into four groups randomly, the images were displayed on four different outputs. Participants were made to match the outputs to a complete set of shade guide. Descriptive statistics were used to assess the proportion of correct responses. Chi-square test was used to test for the presence of statistical association between the groups. Results: For digital shade evaluation, output from the compact camera (Nikon Corporation, Tokyo, Japan) with an effective output of 14 megapixel showed higher number of responses in terms of accuracy, in comparison with other devices which produced digital outputs with a higher pixel density. The shades were identified best on outputs with a higher pixel density of 2560 × 1600-pixel resolution, followed by full HD LCD display (1920 × 1080-pixel resolution). Conclusion: This study recommends digital photography using a 14-MP camera as a minimum specification for shade selection. For display outputs, laptops with a screen resolution of at least 1920 × 1080, calibrated in standard red, green, blue color space is recommended for visual shade selection. Keywords: Color, dental photography, digital shade evaluation, prosthodontics
How to cite this article:
Kumar A, Ramanarayanan V, Harikrishnan D, Sajeev R, Rejithan A, Karuveettil V, Suresh R. The effect of camera and display technology on the reliability of digital shade evaluation. Amrita J Med 2022;18:123-8 |
How to cite this URL:
Kumar A, Ramanarayanan V, Harikrishnan D, Sajeev R, Rejithan A, Karuveettil V, Suresh R. The effect of camera and display technology on the reliability of digital shade evaluation. Amrita J Med [serial online] 2022 [cited 2023 Mar 24];18:123-8. Available from: https://ajmonline.org.in/text.asp?2022/18/4/123/370002 |
| Introduction | |  |
The science of color is an integration of art, aesthetics, and mathematics. The increased visual demands coupled with high expectations of the prosthetic patients have called for a closer scrutiny of the shade selection and its communication process to the technician with the final aim of achieving a harmonious smile in relation to surrounding natural teeth.[1]
The shade-matching process is challenging. Success in shade selection can be achieved when prosthesis is an accurate replica of the shade of the adjacent natural tooth. The technician who fabricates the prosthesis does not see the patient directly and depends on the dentist’s written prescription to select the shade adding to the complexities.[2]
Visual shade selection is the most followed method for shade determination in dental practice but it often results in unreliable and inconsistent results. However, the cost as well as the ease of the procedure makes the visual shade matching more popular. The evaluation of color differs from one individual to another owing to different personal evaluations and interpretations, making it challenging for many dentists to select and communicate the shade effectively.[3] The visual shade selection depends on a series of visual scales. Here, the physical and psychological interacting factors such as stimulation, sensation, and perception of the observer become critical.[4]
Color matching with shade guides is also influenced by factors such as fatigue, emotions, lighting, and metamerism. In addition to this, the result depends on the type of shade guide used, the method of shade determination, age, gender, and experience of the dental professional.[5],[6] Devices such as spectro-photometers, spectro-colorimeter, spectro-radiometer, and colorimeters have been used as an attempt to overcome problems with visual shade matching in dentistry. But these are reported to be expensive and not necessarily error free.[7]
Despite being prone to error, visual shade matching is still preferred because it is relatively cost-effective and less technically demanding. Due to the individual factors involved in the shade selection, a possible alternative is to transfer a record to the technician with the aid of photographs.[8]
Recent advances in photography and computing stemmed from the use of the digital camera and digital display units for color imaging.[8] This device records the color and shape of the object in the form of digital data, which may subsequently be used to reproduce and transmit to a digital display unit.
Various studies have established that the digital photography is a reliable method of shade selection in the clinical setup.[9],[10],[11],[12],[13],[14],[15] But the digital cameras available today differ widely in their specifications and capabilities. There are no established guidelines for the selection of digital cameras for dental shade selection warranting the need for standardizing minimum specifications. Another factor that determines the reliability of the image is the output unit used, which also requires a minimum specification for display resolution and a standard color space for display calibration. Thus, the reliability of the shade selected using digital photography depends on the specification of the capturing unit as well as the output medium.
The objective of this study was to establish an optimal specification required for the digital camera and the display output to be used for a reliable shade selection.
| Materials and Methods | | |
This cross-sectional study was conducted in a dental school in India. The study participants consisted of dental professionals (clinical dental students and faculty) with normal vision. All participants were subjected to the Ishihara test for the presence of any color blindness.[4]
A total of 16 shade tabs were randomly selected from two shade guides for the study [Table 1]. The shades were limited to A and B, as they are the commonly selected shades in the clinical setup. The shade tabs were then equally divided into four groups. The markings on each of the shade tabs were masked with adhesive masking papers. The experiment involved the photographing of 16 shade tabs (VITA PAN Classical shade guide, VITA – Zahnfabrik, Germany) using four different digital cameras [Table 1] and [Figure 1]. Three camera models used were of the same manufacturer (Nikon Corporation, Tokyo, Japan), to reduce the variation in color reproduction due to vendor-specific image processing algorithms, and as a control fourth camera model was a smartphone camera from a different manufacturer (Apple Inc. California, USA). The cameras were put on automatic mode and settings were kept as default. The shade tabs were photographed by keeping an 18% grey card as the recommended background to standardize the color assessment.[16] Standard indoor lighting with cool-white LED lights of color temperature 4000 K was used as a light source to simulate a typical clinical environment. Photographs were taken by fixing the cameras on a tripod (Camgear, CGR_UD, China) to standardize the object camera distance at 40 cm. Normal lenses with an average effective focal length of 50 mm were used in all these cameras to closely match the perspective of human vision.[17] The configurations of all four cameras were standardized by the following settings: image quality (standard), color Space (sRBG), noise reduction controls (off), and active D-lighting (disabled) HDR (disabled) lens corrections (vignette control, chromatic aberration control, and distortion control) was kept off.[18] To mimic a clinical situation, all the photographs were taken by a dental professional with only basic knowledge of photography. All the digital photographs were stored as JPEG files. Images obtained from each of the cameras were then displayed on one of the four different displays [Table 1] and [Figure 1]. The images were viewed in Microsoft photo software on Windows system and on Mac systems; images were opened with preview.
Participants were made to match the outputs with a complete set of shade guide. The participants were informed about the possibility of fatigue of retina cells on continuous staring of the sample. No time limit was given for the whole recording and participants could take breaks. To mimic the clinical situation, the display outputs were kept at a comfortable viewing distance of the participant. No restriction was placed as far as the position of the display was concerned. The participants were free to move around the shade tab on the display output. The results were noted on a custom-made response sheet and the correct identifications made by the participants were noted to identify the best combination of camera and display.
The obtained data were entered, coded, and analyzed using SPSS version 17.0 for Windows. Descriptive statistics were used to assess the proportion of correct responses. Chi-square test was used to test for the presence of a statistical association between the groups. A value of P < 0.05 was considered statistically significant. The study was approved by the Institutional Ethics Committee and informed consent was given by all the participants.
| Results | | |
A total of 100 responses were obtained for the study of which 23 were males and 77 were females. Of the media used for shade capturing, maximum number of correct responses were obtained with Camera 1 (36.25%), whereas Camera 4 gave the least number of correct responses (7.5%). Of the outputs used, participants identified the shades best in Display 4 (30.25%) and least in Display 3 (16%), irrespective of the medium used for shade capturing.
There was a significant difference between the four output groups (Displays 1, 2, 3 and 4) with each of the input groups viz. Cameras 1, 2, 3, and 4, respectively (P < 0.001) [Table 2]. Camera 1 with Display 4 produced the maximum percentage of correct responses (58%) and the responses were least correct with a Display 1 (14%). When Camera 1 was used to capture the shade, the best output was Display 4 (37%). Similar result was obtained when a smartphone camera (Camera 3) was used as the input device with correct responses of 15% with Display 4. A digital single-lens reflex (DSLR) camera used as the input device resulted in a photo display giving the best responses (32%).
Significant differences were also noted when the four input devices were associated with each of the output (P < 0.001) [Table 3]. When a printed output display was used, maximum correct responses (32%) were obtained when the shade was photographed using the smartphone camera. On use of a laptop, smartphone, or laptop with organic light-emitting diode (OLED) display as the output display device, maximum participants identified the shade tab correctly when DSLR camera was used for capturing the photo (36%, 36%, and 58%, respectively).
| Discussion | | |
Aesthetics plays an important role in the success of prosthodontic treatment. Incorrect shade matching accounts for frequent re-fabrication of the prosthesis. The limitations of widely used conventional shade selection methods are well discussed in the literature. The traditional visual color-matching acceptability has been noted to be less than 40%.[8] This is because shade selection is based on visual perception affected by physiological and psychological responses, which can differ according to the environment. This leads to inconsistent and unreliable shade selection.[8] To combat this, newer techniques such as spectrophotometers and colorimeters are adopted. But they are relatively expensive, technique sensitive, and hence, not regularly used in routine clinical practice.[10]
Digital imaging for color matching is now widely used in dentistry.[11] This has led to the popularity of improved image-capturing options using hand-held devices like smartphones.[13] The newer technique of digital shade selections is made possible by the evolution of digital image capturing devices (input), and its transmission through an electronic medium (Internet) to the technician who views it on a computer, laptop, smartphone or by taking a digital print (output). This process is deemed to be easy, economical, and readily available for clinical use.
There are numerous advantages of digital photography when compared to other conventional techniques. First, a digital photograph helps to exactly replicate the color of the restoration due to its high image quality. This is beneficial to capture the accurate color of different areas of the same tooth when compared to conventional methods. Similarly, perception of color is dependent on several factors like source of light, object being viewed, and the observer.[19] Capturing the shade in a digital medium could thus minimize the subjective errors of the observer. There is also error-free communication of the designated shade by the clinician to the technician adding to its advantage.
However, environmental factors can still affect the quality of shade capturing. This can be controlled by following the recommended lighting conditions during shade selection. The use of color-corrected light is recommended. Removal of other distracting backgrounds needs to be considered of and the use of neutral background in the form of a grey bib is recommended. As to define a standardization and to closely match the perspective and angle of view of human vision, usage of an effective focal length of 50 mm is recommended for lenses, to avoid geometrical distortion in images.[20] All the display devices were color calibrated using standard red, green, blue (sRGB) color space to ensure standardization in color reproduction.
In this study, contrary to the popular belief that the higher specification camera gives a better shade reproduction, the percentage of participants who correctly identified the pictures were highest when a compact camera with an effective megapixel value of 14 was used. This may be because the outputs from higher specification cameras had a high number of pixels which eventually forced the display outputs to accommodate images with higher pixel density, causing larger-than-life contrast and clarity in image display. This could have caused the disparity in shade perception. For shade selection, the requirement of megapixels also depends on the output that is chosen to view the image. Higher megapixels are required if the images are required in printed form whereas computer monitors require lower megapixel. A camera with 7 effective megapixel output would give sufficient clarity for 14 × 11-inch sized inkjet prints. In this study, all the files were saved as a jpeg image to ensure the same degree of compression and it was compatible on Macintosh and Windows systems.
Even though no time limits were given to the participants, a short rest period was recommended for the observers. This was to prevent the fatigue caused to the eye. A correlation between the time consumption and success of match was previously reported.[13] Shorter duration reduced the fatigue and enhanced shade selection ability. Therefore, eye fatigue can be ruled out as a potential confounder.[21]
The display resolution of the output unit plays an important role in the digital shade evaluation.[22] Ziefle[14] reported that the higher resolution displays had a higher comfort level, and it increased the visual performance. In this study, it was noted that the participants were able to do correct identification of the shade on an organic LED display that had higher resolution.
When the smartphone camera was used, it was found that the participants were able to correctly identify the print-out of the pictures. This could be because of the lower-than-actual image size when projected on other output devices.
Previous studies have compared agreement between shade captured by digital process and conventional shade guides and were found to be high.[15] A study done by Miyajiwala et al.[23] comparing digital cameras and contact-type instruments also supported the use of digital cameras in shade matching.
The results of this study reveal that digital imaging may be used as a viable method. If used correctly, the method may be used as an objective method by eliminating the dentist factor. It is also possible to identify the exact shade of different surface of the same tooth and can be communicated to the technician without disparity.
| Conclusion | | |
The study concluded that an optimum specification of the camera will be 14 MP. The object may be photographed under the standard white light of 4000K with a neutral color as background. The study reported the ideal output display unit to be a laptop monitor with a minimum 1920 × 1080 resolution, calibrated in sRGB color space.
Financial support and sponsorship
Not applicable.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1]
[Table 1], [Table 2], [Table 3]
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