Abstract
Recently, projector is one of the most common display devices not only for presentation at offices and classes, but for
entertainment at home and theater. The use of mobile projector expands applications to meeting at fields and presentation
on any spots. Accordingly, the projection is not always guaranteed on white screen, causing some color distortion.
Several algorithms have been suggested to correct the projected color on the light colored screen. These have limitation
on the use of measurement equipment which can't bring always, also lack of accuracy due to transform matrix obtained
by using small number of patches. In this paper, color correction method using general still camera as convenient
measurement equipment is proposed to match the colors between on white and colored screens. A patch containing 9
ramps of each channel are firstly projected on white and light colored screens, then captured by the camera, respectively,
Next, digital values are obtained by the captured image for each ramp patch on both screens, resulting in different values
to the same patch. After that, we check which ramp patch on colored screen has the same digital value on white screen,
repeating this procedure for all ramp patches. The difference between corresponding ramp patches reveals the quantity of
color shift. Then, color correction matrix is obtained by regression method using matched values. Differently from
previous methods, the use of general still camera allows to measure regardless of places. In addition, two captured
images on white and colored screen with ramp patches inform the color shift for 9 steps of each channel, enabling
accurate construction of transform matrix. Nonlinearity of camera characteristics is also considered by using regression
method to construct transform matrix. In the experimental results, the proposed method gives better color correction on
the objective and subjective evaluation than the previous methods.
