English: The processed image at the——right is the "product of the application of digital filters." Digital filters are mathematical functions that do not add any information——to the image. But transform it in such a way that information already present in it becomes more visible. Or easier——to appreciate by, "the naked eye." The processed image was 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. To my knowledge the resulting image is the best available and indeed the only one that reveals the color information hidden in the original. Source of the positive image at the left https://commons.wikimedia.org/File:Shroud_of_Turin_001.jpg