I’m taking photographs of paintings on a white wall, and I am post-producing them for use on a website.
Very often I’m asking myself “Is this the right brightness? Too dark? Too light?”.
I know that nothing replaces:
experience (know how your own monitor renders well known photos that are well balanced)
having a calibrated monitor (I already did this)
testing the photo on many devices (I do test on various PC laptops, iPad, Macbook, smartphones, etc.)
What other techniques (possibly as objective as possible) help you to determine if a photo is too dark, too light?
(I sometimes give a look to the histogram, mostly to know if nothing is “burnt” in highlights, but I haven’t found a reproducible method that works 100% to determine is a photo is too light or too dark)
NB: the main problem is that most devices (smartphones, laptops) have a variable screen brightness setting (I often change it accordingly to the room light, and, in the case of the phone, it can even change brightness automatically), so at the end you never know if the brightness condition of the device is good to evaluate the brightness of a photo.
Example here: how to determine which one of these 4 variations would be best adapted for most users?
When you photograph any well (evenly) lit object against a white wall, you diminish the contrast by introducing flare from the reflection of light from the wall into the lens.
Ideally, you would use a neutral (18%) grey b/g to minimize the amount of flare to preserve the contrast. Even better would be a matte black background for the same reason. Set the exposure from a reading from an 18% grey card at the surface of the artwork.
You would then close crop the image and add the white b/g in post for the Web display.
After you get a balanced (check the histogram) image, use that one.
Lighting is better if you use two balanced sources on either side of the artwork at 45° to the original so as to minimize reflections from the flat artwork surface.
When the image looks okay on your calibrated screen, you’re good to go. Each user will have to adjust their screen for their conditions, good or bad — You can’t take responsibility for remote locations.
Definition: A well-exposed photographic image has a full range of tones and shows detail in the darkest and lightest areas of the image (specular highlights excepted).
Recommendation: A good (not perfect) photographic colour reference is an X-Rite (brand) ColorCheker™ which is made from stable pigments (24 of them) free from fluorescent, ultra-violet, and metameric visual contaminants so they photograph as they appear visually. They’re EXPENSIVE but for a good reason. Tip: include one in every photo to ensure consistency.