If you are making a positive into negative image, here is how it is;
- Posterization. This effect was once done in the darkroom with separate negatives that, when printed together, reduced the tonality of an image to only a few tones. This filter lets you choose the amount of tonal levels to make a posterization, though usually 2-4 are sufficient. Too many will look too much like a conventional photograph. This effect works particularly well with black-and-white images.
- Threshold. Use this filter to immediately convert an image to high-contrast black and white. To control the level of threshold, adjust the filter's histogram