*3.3. Human Subjective Evaluation*

The color sensation is commonly considered as a subjective feeling of human beings. In this work, a human test is carried out to evaluate our color enhancement approach. The procedure consists of an image re-coloring stage to produce the CVD-friendly output, and an evaluation stage to analyze the responses collected from the volunteers. In the human test approved by an IRB (institutional review board) [38], people with color vision deficiency were asked to give judgments for the images enhanced by the re-coloring algorithms. We first let the subjects understand the purpose and process of this color test clearly. Three types of color vision deficiencies: protanopia, deuteranopia and tritanopia are considered, and the subjects are classified to groups for testing. Four different approaches, *M*1, *M*2, *M*3, *M*<sup>4</sup> are then evaluated as follows.


We collected 55 valid subjects in the test. The results are tabulated in Table 4. In the table, *i* is the method of different research stages, *j* is the index of the test image, the letters are the feeling level of the pros and cons (denoted by A, B, C, D) for the subjects. The summary indicates the proportion of the method *Mi* for the test image *Fj* chosen by subjects is over 1/3. As shown in Table 4, 83.64% (marked in blue) of 55 subjects selected level A for the method *M*<sup>2</sup> and the test image *F*1. The numbers marked in red indicate the proportion of method *Mi* in levels A, B, C, D with higher percentages, and the associated methods are more representative in the level. Thus, each level (A, B, C, D) is represented by the methods: *M*2, *M*4, *M*3, and *M*1. It also shows that the best to the worst for color vision deficiency feeling of the four different methods are given by *M*2, *M*4, *M*3, *M*1.

**Figure 16.** The comparison of CVD simulation results processed using our re-coloring technique and Kuhn's method. The first and fourth rows are two test images and their CVD simulation results. The second and fifth rows are the visualized RMS values, and HDR-VDP evaluation is shown in the third and sixth rows.


**Table 4.** The human test on 55 valid subjects with four different methods. The number are shown in percentage. The numbers marked in red indicate the proportion of method *Mi* in levels A, B, C, D with higher percentages, and the associated methods are more representative in the level.
