Film colors were determined with a Minolta Chroma meter (CR
300, Minolta Chroma Co., Osaka, Japan). A Hunter Lab color scale
was used to measure the degree of lightness (L), redness (þa) or
greenness (a), and yellowness (þb) or blueness (b) of the
films. The instrument was standardized by means of a set of three
Minolta calibration plates. The films were measured on the surface
of the white standard plate with color coordinates of L¼97.3,
a¼0.14 and b¼1.71. Total color difference (ΔE) was calculated
from
ΔE ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðLf ilmLstandardÞ
2 þ ðaf ilmastandardÞ
2 þ ðbf ilmbstandardÞ
2
q
ð2Þ
Values were expressed as the means of nine measurements on
different areas of each film.
2.6