Usually in the field of image quality assessment the terms "automatic" and "subjective" are often incompatible. In fact, when it comes to image quality assessment, we have mostly two kinds of evaluation techniques: subjective evaluation and objective evaluation. Only objective evaluation techniques being automatizable, while subjective evaluation techniques are performed by a series of visual assessment done by expert or non-expert observers. In this paper, we will present a first attempt to an automatic subjective quality assessment system. The system computes some perception correlated color metrics from a learning set of images. During the learning stage a subjective assessment by users is required so that the system matches the subjective opinions with computed metrics on a variety of images. Once the learning process is over, the system operates in an automatic mode using only the learned knowledge and the reference free computed metrics from the images to assess. Results and also future prospects of this work are presented.
CONTEXTWhen it comes to image quality assessment, we have mostly two kinds of evaluation techniques [20] : subjective evaluation and objective evaluation. These evaluations can be done with a priori information (with reference) or without use of a priori information (reference free). Subjective approaches, which to date are the only widely recognized method of determining actual perceived quality, are complex and time-consuming, both in their preparation and execution [21]. Subjective evaluation is formalized with defined procedures [20]. Objective quality evaluation use metrics to evaluate image quality. Objective evaluation is automated, hence it costs less than a subjective evaluation, plus it can be done in real-time since it needs no user interaction. Objective quality metrics can be full reference, reduced reference or reference free [21] Moreover, automatic objective assessment systems do not necessarily correlate well with perceived quality [20,21]. Ideally, a quality assessment system would perceive and measure image or video impairments just like a human being. As long as quality metrics are not correlated with human perception, subjective evaluation is still mandatory. This explains why in some domains such as photography and old film restoration, where there is no reference to compare to, subjective quality evaluation is the most reliable technique used. In the last works we presented some original reference free metrics [22][23][24][25] that correlated well with human perception (metrics for contrast and color quality based on statistical and perceptual approaches). These perception correlated metrics were a first step to bridge the gap between subjective and automatic approaches. In fact, since perceptual correlated metrics are available, automatic computation and learning -and hence automatic assessment-become possible.In this paper, we will present a first attempt to an automatic subjective quality assessment system. The system computes some perception correlated color me...