I took a quick whirl at it as well, and using the levels command (using the histogram) was able to get the background darker and still keep some of the detail in the hair.
Bon, I find your image slighly overexposed, there is a white haze to the image, the background, i feel would look better as black, i think, you could do one of two things to your images to correct this. Post processing you could increase the contrast, thus darkening the background, this also increases the highlights, so bring the brightness down a few steps to compensate, OR, you could try forcing your camera to underexpose by say 1/2 a stop, this will increase the contrasts in the image, and reduce the white haze I have mentioned. I have had a quick try with your image with what I suggested above, and got the result shown, the face appears alot darker but I feel the rest of the image and the model is alot cleaner. I am interested to hearing your response Russell
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