I wanted to follow up on the contrast issue brought up earlier, so I took a large number of samples to examine exactly what's going on. Here's what I found. First, here's the photo I'm using as a sample, in an ideal colour-corrected representation:
Next, some JPEGs straight out of the camera showing uncorrected results. All images were shot at f/4.5 at 0.4s, ISO 80.
Black backing on both sides of the cradle
White backing under photo, black backing on reverse
White backing on both sides of cradle
At a glance, you can see that the contrast is mostly similar in the first two, but very washed out in the third. Here's their histograms:
White + black mix
It's clear that the all-white image is being overexposed, contributing to the washed out look. However, even if I compensate for that:
It becomes evident that the all-white background version is still looking too bright in the dark areas. It looks like the problem is reflection from the cradle itself - a bright cradle is reflecting light onto the other side of the cradle, resulting in brighter dark tones.
The all-black version also exhibits less visible noise. The following two examples are full-sized crops enlarged a bit, taken from the raws, with the same processing applied to each and noise filtering turned off.
All black background
All white background
The noise may partially be due to my original hypothesis about light being reflected into the lens from the background, because if you compare these shots from the all-black and black opposite, white facing versions:
There's colour artifacting showing up in the version with a white background facing the camera, even though it has the same contrast thanks to the black background opposite the photo. You can also see that the all-black background version has visibly lower luma noise.
This is irrelevant to anyone not shooting raw, but I've also found that the versions with black under the photo itself provide better results in pumping up the blacks, which is necessary in this environment to obtain a lifelike level of dark colour when shooting documents. The all-white background version requires a much higher setting, and ends up with worse results.
To summarize the tl;dr version:
- A black background under the item being shot reduces noise, resulting in a better image
- A black background opposite the object being shot reduces light reflections, resulting in better contrast
The opinions expressed in this post are my own and do not necessarily represent those of the Canadian Museum for Human Rights.