Equation to related W to L* then became,
L*=(W+31.9)/1.40 (1)
To change L* to luminance Y we used the following equation
Y/Ya=((L*+16)/116)3
Where Ys is the luminance for a standard white . We know the whiteness amount of the wall from the work of Mookrai et al. 5). We employed the data obtained under 80 lx of experimental room and for the shelf depth of 30 cm and calculated Y/Ya values to be reproduced on the photograph. The luminance of eight points on the front wall of the real room as well as of the photograph was measured by a luninometer Konica Minolta CS-100A. We used the highest luminance at an upper position on the wall as Ys.
The results of Y values are shown in Fig. 2. The abscissa is the distance on the wall from the floor and the ordinate the luminance Y. Two dotted vertical lines indicate the shelf width seen by a subject. The triangles represent luminance of the real room. There is difference in luminance between walls below and above the shelf. When the whiteness amount was transferred to the luminance for the photograph of the room it became curves shown by circles. Below the shelf luminance is much higher than the luminance of the real room.
The final step of this experiment is to modify the photograph of the real room to meet luminance shown by circles in Fig. 2. Photographs of the front wall of the real experimental room were taken by a camera and they were modified by using the level tool of Photoshop CS5.1. After printing out the photographs the luminance was measured at positions given in Fig. 2 to arrive at the luminance given by circles. This was done by trial and error.
The results are shown in Fig. 3. This is a view of the front wall of the experimental room. On the shelf some objects were placed to simulate a normal room. Along the two vertical lines numbers were marked to locate the positions for measurement of luminance and for the elementary color naming.
The left is a photograph before modification of lightness and a dark shade under the shelf can be observed. The right is the photograph that was modified according to the brightness impression. The shade under the shelf is reduced to meet the perception. Interior designers can explain the interior atmosphere more properly to clients by using modified photographs like the picture on the right.
References
1) M. Ikeda, H. Shinoda, and Y. Mizokami. Phenomena of apparent lightness interpreted by the recognized visual space of illumination, Opt. Rev. 5 (1998) 380-386
2) P. Pungrassamee, M. Ikeda, P. Katemak, and A. Hansuebsai: Color appearance determined by recognition of space, Opt. Rev. 12 (2005) 211-218.
3) C. Phuangsuwan, M. Ikeda, and P. Katemake: color constancy demonstrated in a photographic picture by means of a D-up viewer, Opt. Rev. 20 (2013) 74-81.
4) C. Phuangsuwan, S. Moolai, and M. Ikead: Lightness constancy by using real space environment, Jr. Col. Sci. Assoc. Jpn. 37 (2013) 562-563.
5) S. Mookrai, C. Phuangsuwan, and M. Ikeda: Lightness constancy demonstrated by using real space and various shadows. (Accepted for publication by Jr. Col. Sci. Assoc. Jpn.)