They say good light is when light is soft, during those rare hours of the day. And bad light is harsh light, where the light is straight on in the middle of the afternoon.

That all seems to make sense but why is it that computer cannot fix this? Isn't this a matter of contrast? If the light looks harsh doesn't that just means the contrast is too high? Can't the software make it a smoother gradient?


3 Answers 3


The problem is the software can't distinguish between a gradient on your shirt, different colors of leaves and an actual shadow. Software is great at finding edges by looking at the contrast, but it has no idea what those edges correspond to. If the image was reproduced in actual 3d and the software knew the light source and what kinds of shadows things would cast, then in theory, it could do what you are talking about as long as sufficient detail was captured (this is basically how 3d rendering software works), but that information simply isn't available from a normal photograph.


While many folks use the term "bad" for harsh light, and good for soft light, these phrases are not accurate. Most people look better in soft light. Harsh light has very strong contrast and can accentuate features, like wrinkles, that we don't like in people.

But harsh light can be just exactly what some photos and/or subjects require. This strobist article shows some excellent results from harsh light. http://strobist.blogspot.com/2007/02/on-assignment-speedlighting-college-gym.html

With hard light, there are sharp shadows, and very quick transitions between light and deep shadow.

It depends on what you mean by "computer fix". A computer can do anything that a programmer can tell it to do. So it can lighten up the dark areas. But it can't change the dynamic range that the camera captured. And it can't tell if the dark area (say under the chin) was wanted or the same as a very dark piece of background.

If you are really asking if a talented human using something like Photoshop could fix it in post, the answer is yes. But it may not be worth it for most photos.


The reason a computer cannot "fix" harsh lighting is because of the nature of the shadow's edge in harsh lighting. The difference between harsh and soft lighting is not simply a matter of contrast, it is a matter of grade. There is a contrast factor, however that is the result of the gradient, and it is a structural and local phenomena, not a global one nor a micro one.

You have a quick gradient between shadow and non-shadow with harsh lighting, while you have a gradual gradient between shadow and non-shadow with more diffuse soft lighting. There is absolutely nothing a computer can do about that, unless you intend to manually paint in a softer gradient yourself, taking into account all of the various contours of whatever it is you are shading. The nature of light, and how it shades a surface, is a matter of the light interacting with those surfaces. Assuming you had DETAILED information about the physical structure of each object in your scene, as well as detailed information about each and every light source, and the position of the camera relative to them all, then you could probably have a computer reconstruct the appropriate shading. That is a lot of information you are never going to have, though.

If you need a certain kind of lighting in your scene, you need to apply it in the scene. There really is no way to correct the wrong kind of lighting in post. It should also be pointed out that there is no such thing as good or bad lighting, really. It really depends on your goals. Harsh light is often selected explicitly for use in portraiture, as much as softer and diffuse lighting, or even combinations of a variety of types of shading.


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