Image: Shroud of Turin
Positive and negative images of the Shroud of Turin. The image on the right was digitally produced by inverting the brightness of the pixels in the positive image but without inverting their hue, and then by increasing both the brightness contrast and the hue saturation. Finally noise and so-called “salt and pepper” filters automatically removed the noisy information from the original image which hinders the appreciation of the actual face.
credit: Dianelos Georgoudis / Wikimedia Commons