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How are photography and xerography based on photochemical processes?

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Underwater view of a glowing chain of tunicates with a scuba diver and boat visible near the water's surface in the background. — photochemical reaction Chain of fluorescent tunicates.

Photography and xerography are both image-forming technologies that rely on the interaction between light and specific materials, though they utilize different physical and chemical principles to create an image.

Photography

Traditional photography is based on the light-sensitivity of silver salts, such as silver bromide, which are coated onto a film base. When light from a scene strikes this emulsion, it triggers a chemical change that creates an invisible [latent image]. During the development process, the silver salt crystals that were exposed to light are chemically converted into metallic silver, forming a visible, tonally reversed negative image.1

Xerography

In contrast, xerography is an electrophotographic process that relies on photoconductive substances, such as [selenium]. These materials have an electrical resistance that decreases when exposed to light.234

The process functions as follows:
* A photoconductive surface is given a uniform electrostatic charge in the dark.2
* When a light image is projected onto this surface, the photoconductor allows the charge to leak away in the illuminated areas, leaving an electrostatic "image" charge.2
* This latent charge pattern is made visible by applying an oppositely charged powder, known as toner, which adheres only to the charged areas.32
* The toner is then transferred to paper and fused with heat to create a permanent image.342