Why would a camera change colors on the image when producing JPEGs?

Question

There's a room with windows closed by curtains, it's night outside and the only light source is a set of LED filament lamps inside the room. Lamps are designed to have 2200K color temperature to have "retro" look and so light is notably yellowish and all the scene lit by these lamps also looks yellowish to an eye.

Then there's a point-and-shoot digital camera with "scene modes" like "sports", "sunset", "landscape" and the like. Camera can only produce JPEG, so all post-processing is done inside the camera.

Camera positioning and focal length is the same during all filming so camera sees the same scene all the time.

In "landscape" mode the resulting shot is not yellowish — it looks as if it was lit by a 4000K-6500K color temperature fluorescent lamp. In "sunset" mode the shot looks yellowish more or less the same as what an eye sees.

So post-processing behaves differently. It deliberately changes colors in "landscape" code. Why would it do so?

It's not something like automatic exposure where a camera cannot know the expected brightness of an object and so guesses how bright is should look. If the camera doesn't do that we would have to either manually set exposure or have a ton of severely overexposed or underexposed shots.

Visible color of an object looks like something objective — if it looks yellow then it looks yellow, why change it in the first place? I just don't see how this color alteration is useful.

Why does a camera alter the colors in the entire scene during post-processing?

Answer 1

Visible color of an object looks like something objective — if it looks yellow then it looks yellow, why change it in the first place? I just don't see how this color alteration is useful.

This is the fundamental misunderstanding. Visible color is not objective at all. That sounds surprising if you haven't really stopped to consider or investigate, but it really is the case. Remember the blue/yellow dress?

"Color" is actually a sensation that arises in the mind, not a physical property. Unlike, say, scent, which relies on specialized receptor neurons for each smell, color is largely the result of complex subconscious processing in the brain. Our color perception is very dependent on situation. (In more depth, see this answer to a different question).

So, that's the first thing. The camera can't just show you "true color", because it's just a dumb mechanical device. In some ways, the post-processing it does to create a JPEG mimics human color perception (because, hey, these cameras are made for humans), but fundamentally a lot of decisions are up in the air. This is why white balance is a user-selectable parameter even on the most primitive digital cameras, and on the ones where just about everything else is always automatic.

Related to this, then, is the matter of taste in processing for different subjects. For example, it's usually the case that when photographing people, we want to mute color a bit to downplay skin blemishes. And for landscapes, people often want pushed up colors to make greenery or fall foliage or rock formations or whatever stand out.

Your camera's scene modes are black boxes — you can't see what affect they actually have, beyond guessing from the name and the manufacturer's description. But they definitely do guide the camera's choice in color processing. It sounds like in your case, it also affects the camera's assumptions about white balance (which is fairly reasonable, as a landscape is not normally lit by candles).

If you're not happy with that, it's best to avoid scene modes. The ultimate version of this, of course, is shooting in RAW. You note that your camera can't do this, so it may just have to be a limitation you must accept for — but something to consider for now next time you get a camera.

See also Are scene modes, white balance, color tones, and similar just post-processing effects?

Answer 2

It's the effect of changing the white balance that you are seeing in the color shift of the different modes. The camera has to guess the white point of the image in order to render the JPG in automatic mode. In the Landscape mode it is guessing you are outside under natural light. In Sunset mode it guesses the light is yellow at sunset and renders the colors accordingly.

The white point is the RGB values that define what our eyes see as white. But the camera can only capture what its sensor sees, so it doesn't know how we perceive white in the scene. It makes its best guess as to what is white instead.

This is one reason photographers use RAW -- you can change the white balance to whatever you like in post processing. If you have the camera process the RAW image itself to produce a JPG, it has to guess the white balance.

Check your camera to see if there is a white balance setting you can control. You may be able to manually set white balance to get the colors you want.