Colour appearance assessment for dissimilar sizes

The colour size effect is an important aspect of colour appearance phenomenon, in which the colour appearance is changed according to different sizes of the same colour stimulus. Although colour appearance has been actively researched over the last 20 years and models have been developed capable of predicting the colour appearance under a wide range of viewing conditions, the colour size effect was not taken into account due to lack of reliable colour appearance data for colours with various sizes. This lead to great difficulty for industry for faithfully reproducing colours between dissimilar sizes. In this study, it is intended to accumulate colour appearance data for various sizes, to analyse the size effect and develop a model to predict size effect in purpose of accurate colour appearance reproduction across dissimilar sizes. Colours in six sizes, including the size of a real room, were divided into two groups and were assessed by a panel of observers. The techniques of magnitude estimation and asymmetric colour matching (by using CRT and physical colours) were applied. Totally, there were 4920 assessments conducted for various field sizes by using different scaling techniques under different viewing conditions. The colour appearance of the room was investigated in two aspects: size effect and mixed illuminant based upon both physical measurement and psychophysical visual experimental results. For the former, colour appearance between the room and 10° size were compared and modelled. For mixed illuminant prediction, a mathematical model was developed to predict the adopted white for a room with any wall colour. Finally, a model for predicting colour appearance for room colours was derived including three parts: the illumination prediction, colour appearance model (CIECAM02) and size effect correction. The size effect was further investigated using the visual results from all different six SIZ es. Based upon the CIB recommended 2° and 10° standard colorimetric observers, the colour appearances of object samples were predicted. The changes of colour appearance for those colour samples from one size to another were analysed. Most importantly, the relative changes of colour appearances of six dissimilar size colours were also revealed based upon proposed experimental results. A clear trend was found that colour appears lighter and more colourful with the increase of stimulus size, there is however little change in hue. Finally, colour appearance models that are capable of predicting colour size effect for any sizes of colours were developed. They were firstly derived based upon both CIELAB uniform colour space and CIECAM02 colour appearance model, which were named as size effect correction model. Another model, named as size effect transform model, was also developed based on human cone response functions. By using those size effect models, the colour appearance for dissimilar sizes can be predicted incorporate with colour appearance model . These models can also successfully predict the visual results.