Will filters help me get more accurate color when photographing my paintings? I have problems especially with reds and especially if there are no strong contrasting colors in a red painting.
Probably not. Color filters can be useful when you want to get a certain look in a black and white photograph, but usually don't enhance color. That's because they are inherently restrictive — they subtract colors from the scene.
Probably what you need is a) better lighting on the painting and b) to shoot in Raw so you can make careful adjustments to bring out those subtle differences in reds.
It's a good idea to color-calibrate your monitor, and the suggestion of working with a color target for accurate color isn't a bad one. And, definitely do not use automatic white balance — set it manually to the color of your light source, or use a gray card.
I should also mention that a filter can help with one thing: if your paintings are reflective (oil paints, say), using a polarizing filter on your light source and on the camera may be helpful. There's a good tutorial on that at http://chsopensource.org/2013/02/27/polarized-light-photography-for-art-documentation/. but from your description, this isn't the issue you are dealing with.
I'd recommend getting a colour swatch such as the X-Rite Color Checker Passport. If you take a photo of your painting with the device in shot, this acts as a reference for all other photos taken with the same lens and lighting conditions, and ensures the colours are as accurate as possible.
The device comes with a stand-alone application and a Lightroom plugin so you can use the reference image to create a profile, which you then apply to all the images from the shoot. You should be aware that the standard white balance settings in your editing software don't always work once you've applied the profile but the device has grey and tinted patches to allow you to use custom white balance tools to tweak the image to get the required effect.
The problem is most likely white balance. Your camera can't tell the different between a grey painting in red light and a red painting in white light. If it sees a lot of red, it'll probably assume it's in red-ish light and will "correct" away some of the redness.
A simple solution is to photograph a piece of white paper or plastic (make sure it really is white and not some off-white colour) in the same light before photographing your painting. Shoot in RAW mode and tell your RAW file convertor or image editor to make that piece of paper white. Then copy the white-balance settings to your painting. A more advanced solution would be to use a proper photographic grey card or a device such as the one that Nick Miners suggests in his answer.
Filters will definitely help, contrary to the other answers. Let me explain this (and I assume that you shoot in RAW. the only proper way to go.)
Let's say you have an average RGB value of (95%, 25%, 10%) through the entire picture. This is basically a heavy red color cast over the image. Now,
- RED is being digitized using the ~95-100% of the dynamic range of the ADC,
- GREEN is being digitized using the ~25-30 % of the dynamic range of the ADC,
- BLUE is being digitized using the ~10-15 % of the dynamic range of the ADC.
So in effect, your Red color resolution will be fine, Green is more coarse, and Blue is even worse (around 4 bit color intensity loss compared to Red).
Now you can do four things:
- Clip at Red - meaning your Green and Blue will have inferior resolution - the scenario above,
- Increase exposure value so that Green and Blue are at around 90%, but that means your Red will be overexposed, and much of detail will be lost
- You create HDR from several shots. This is actually a workable way, but make sure you do not keep shooting overexposed images for long, because you can burn a pixel out accidentally.
- You filter out Red! So you basically reduce the intensity of Red from 95% to be around the same as Green and Blue, something around 25% should be fine. Then you will have correct exposure levels for all channels. (Ideally, you should have the same for R,G and B...) Then at home, you compensate against the filtered color, and you will basically have a HDR image with fine color resolution. You compensate by using a color reference chart, taking a picture with filter on.
Now, the described process is about Red, but you can compensate against any color cast to have a better dynamic range photo at the end. Do I recommend this?
- If you do shots that require a specific shutter, and you cannot repeat the very same shot, yes, go with filters, just make sure your color processing flow is working! (Test before you make your production shots.)
- If you can create multiple shots, go for HDR. This is a much better way to collect all the color information there is available. Use a color reference again if needed, and also understand that you will have a HDR image at the end, so you will have to do some dynamics compression of some sort. But if you paint, that HDR image will convey far more information than the other three methods.
Traditionally the technique for photographing prints and paintings is called "cross polarization", where you have polarizing filters on both the lens and the light sources. This helps prevent glare (which washes out detail and color).
The setup is a little complicated, but you want two lights set at 45 degree angles from the artwork, and the camera set back to avoid reflections from the lights off the stand or art board. The polarizing filters on the lights should be set at the same angle/orientation and the orientation of the filter on the camera lens should be offset from the ones on the lights by 90 degrees (or so).
If you google "cross polarization art photography" you should run across several tutorials that give practical advice for setting up the filters, etc.
I specialise in photographing paintings and most of the above are good suggestions. Definitely start with a white balance for the lighting you are using and for super accurate colours a Q card OR colour checker passport would be essential. BUT all this is out of the window and a complete waste of time unless your monitor is calibrated. The mention of polarising the light [should you be using studio lighting] as well as the camera for the more trickier of oil paintings, is a recommendation too, but only used in extreme cases. Good luck