作法: 
	用GIMP(open source)
	取得histogram: 			Colors -> Info -> Histogram，截圖存檔
	histogram equalization: Colors -> Auto -> Equalize， export as -> 存檔

input file: 
	./0_before_left_dark.jpg
	./0_before_left_light.jpg
	./0_before_right_dark.jpg
	./0_before_right_light.jpg
original_histogram:
	./2_before_left_dark_histogram.png
	./2_before_left_light_histogram.png
	./2_before_right_dark_histogram.png
	./2_before_right_light_histogram.png
output_photo:
	./2_after_left_dark.jpg
	./2_after_left_light.jpg
	./2_after_right_dark.jpg
	./2_after_right_light.jpg
new_histogram:
	./2_after_left_dark_histogram.png
	./2_after_left_light_histogram.png
	./2_after_right_dark_histogram.png
	./2_after_right_light_histogram.png