2010 Volume 9 Issue 5 Pages 231-240
Using digital photos in RAW format, we previously reported that the ratio of Blue and Red (B/R) in digital photos is useful to a marker of purity of air in day time. Namely B/R of fine sky is larger than 2.0 and ratios of green and red (G/R), and blue and green (B/R) of fine sky are larger than 1.5. Recently file sizes of photos taken by a digital camera can be reduced by JPEG format. The effect of the file size reduction on the B/R value is analyzed by changing reduction rate. No significant refraction of the file reduction effect was observed for the case of 50% reduction rate. A digital camera is included in some mobile phones. Photos taken by digital camera are usually stored in JPEG format to reduce file size. A variety of B/R values was observed in 20 photos taken by 8 different cameras on mobile phones. The standard deviation of B/R values is almost 10%. 3D scatter plots of data by G/R, B/R and B/G showed that 20 data are lying on a plane except for one point. A new marker is necessary to compare B/R values of different photos taken by different cameras.
