Reversal film, thanks to its special development, immediately produces a positive image with correct brightness and color, unlike negative film, whose brightness and color values after development are opposite to those of the photographed motif and only corrected by the positive process. This makes it the analog image carrier that shows us directly what we have exposed and how, without the copying process that is fraught with the possibility of falsification.
We first develop the reversal film normally, without fixing it. Instead, bleaching removes the silver image, leaving only the previously unexposed silver halides in the layer. These are then transformed into development nuclei by a second exposure, which can also be carried out chemically, and again converted into metallic silver by a development bath. Now, the originally exposed areas are clear and transparent, while the non-exposed areas are dark, reflecting the pattern of brightness values positively and correctly.
Therefore, the secret to reversal film lies not in the emulsion itself, but in the special development. With it, practically any black and white negative film can become reversal film. To make this possible, it is first developed normally and the resulting silver image is removed by bleaching. In the next step, the still undeveloped silver halide crystals are second-exposed and developed. The resulting silver image is a positive. Normal color negative films, on the other hand, are unsuitable because the reversal film requires dyes with special spectral properties that are not present there.
Silver films are essentially digital image carriers; electronic image carriers initially work internally in analog!
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