I’ve noticed that pictures that I take of my work in my studio are often brighter than the painting looks. I don’t know the exact reason and it’s easy to fix in Photoshop but here are some possibilities.
The cameras settings can easily create brighter images. There are several reasons for this. The imaging chip reacts to light differently from our eyes. The camera is capable of imaging darker shadows than our eyes so a very dark colour looks lighter through the camera.
The lighting in my studio is fluorescent. It’s full spectrum fluorescent but it still has a heavy green spike. All fluorescent bulbs have this. You don’t usually see this through a digital camera because all digital cameras compensate for light temperature. If you have ever used a film camera you have seen this. Pictures taken under fluorescent light have a green tint. Incandescent bulbs emit a cooler colour spectrum and subsequently have a yellow or red tint. I know this will seem wrong to many of you. Blue and green light has a higher temperature that yellow or red light. You could buy different film if you were using incandescent light (artists normally call that warmer). The different light spectrum may skew the image histogram to a lighter tone. Professionals using digital cameras take a photo of a colour chart that includes a white section. The camera can take a reading from the white section and give a proper colour balance for the image (this is usually done automatically).
My monitor may be set so that an image appears brighter. This is actually easy to set. Take a digital photograph of a colour chart, put it up on the screen and compare it to the original. Most monitor software has the ability to adjust the colour rendering. I use my monitor while painting because prints can’t reproduce the colour spectrum that a monitor can. I adjust the screen images to something I like and paint accordingly so I’m already compensating to some extent.
The light reflection off various paint may also contribute to the problem. Light and frequency reflection is a complex subject. Some of the pigments we paint with are somewhat iridescent; like a butterfly wing. This is a quantum effect that changes the frequency slightly depending on the direction it is viewed from. It’s not something we usually want but there are iridescent paints out there so be aware of them and experiment.
Complex! But make it simpler. Get the image up on your monitor, tweak it in whatever way you can until you like it. Now paint from it. I still use a printed image but I compare it to my monitor and paint accordingly. When I take a picture of the painting I adjust it until it looks like the painting. I still can’t guarantee that what you see on your monitor will match the painting exactly but no matter what I do I can’t guarantee that.