Early photographic processes were only sensitive to the blue end of the visible spectrum. It took many years after photography was developed for chemists to cre

Early photographic processes were only sensitive to the blue end of the visible spectrum. It took many years after photography was developed for chemists to create dyes sensitive to red and green. Using only the blue channel from a color image is an easy shortcut to obtaining the look which is sometimes done to depict someone as rugged, aged, and weathered for artistic effect. Here's an article on simulating this look digitally, from the same publication. https://petapixel.com/2019/04/05/recreating-the-look-of-1850s-tintypes-in-digital-with-math-and-science/ https://petapixel.com/2019/04/05/recreating-the-look-of-1850...