X-ray film is a special type of photographic film that is optimized for recording X-rays. A polyester carrier film is coated with photographic emulsions, usually based on silver bromide with an ordered silver crystal structure. The crystals provide a resolution in the single-digit µm range. Lead foils are used for amplification, especially at higher energies, with their thickness determining the blurring. The maximum permissible energy and the thickness of the foils are regulated by standards, e.g., in ISO 17636-1:
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From this, the requirement for spatial resolution of digital images is derived in Part 2:
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In addition to spatial resolution, contrast resolution and dynamic range are also important. ISO 11699-1 describes several film classes with different sensitivities (the dose required to achieve an optical density of 2).
The luminance range behind the film can be 6 orders of magnitude. In contrast to medicine, where the dose exposure to tissue should be as low as possible, image quality is the primary concern for industrial film, so that evaluation should only begin at a density of D=2.0. The maximum density is limited to approx. D< 5, as light boxes and the human eye set a limit.
Wire or step-hole indicators in accordance with ISO 19232 are used to determine image quality. If the required wire is recognizable or the required hole set is visible, the image quality is acceptable.