Stuart's take
Film's depth is microscopic, but it's real. Part of it is the ink sitting on the paper, part of it is how light changes the density of the silver halide crystals, and every time light is exposed onto something, it freezes that moment and adds another layer.
Pass one: what happens when light hits film?
Color film is a stack. In a typical color negative, a blue-sensitive layer sits on top, then a yellow filter that stops blue light from reaching the layers below, then the green-sensitive and red-sensitive layers. Each layer forms its own dye when developed: yellow, magenta, and cyan. A digital sensor is a single flat layer under a grid of color filters.
Film layers are also built from crystals of different sizes. Larger crystals are more sensitive and make coarser grain, smaller ones are slower and finer, so grain varies with exposure across the picture.
As one layer develops, it can hold back development in its neighbors. These interimage effects increase the separation between colors.
Pass two: what does printing add?
A print is a second exposure: light goes through the negative onto light-sensitive paper, and the paper has its own response curve on top of the film's. Slide film skips this step, because the slide itself is the final image.
Pass three: what happens when you look at a print?
Light from the room goes down through the dye, hits the white paper, and bounces back up through the dye to your eye, so it crosses the dye at least twice. Some light also scatters sideways inside the paper and comes out under neighboring dye, which softens edges at a scale too small to see as blur. A screen works differently: it gives off its own light.
What's halation?
Bright light can pass through the film, reflect off the back of the base, and come back into the emulsion, making a glow around highlights, often reddish. Most films have an antihalation layer to reduce it. CineStill 800T, made from Kodak motion picture film with its antihalation backing removed, is known for exactly that red glow around lights.
Why isn't color the answer?
Because color depends on the viewer and the room as much as the photo. Your eyes adapt to the light around you, so the same photo looks different on your phone outside at noon than in bed at night. Screens change too, with brightness and night modes. And about 1 in 12 men and 1 in 200 women have some form of color vision deficiency.
Stuart's take
That's the same rabbit hole people fall into mixing songs. Color is the wrong dragon to chase. Analog warmth in music is the equivalent of the depth in film, and people are building supercomputers to chase color when there are easier ways to get at depth.
None of this makes digital worse. It's one capture and no dye, where a film print has three crossings of light. In Stuart's view, that difference is the depth people notice and can't always name.
Frequently asked questions
What makes film look different from digital?
Layered capture, a second exposure in the print, and light passing through dye on paper twice when you view it. A digital photo on a screen is one capture shown as emitted light.
What causes halation in film photos?
Bright light passes through the film, reflects off the back of the base, and re-exposes the emulsion, making a glow around highlights. Most films have an antihalation layer to reduce it.
Why does the same photo look different on different screens?
Your eyes adapt to the surrounding light, and screens change with brightness and night modes. About 1 in 12 men and 1 in 200 women also have a color vision deficiency.