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If I take portraits against a white background I like to use a colorchecker passport to ensure that my subjects come out at the end of my workflow looking 'true to life'.

The problem is that due to whatever reasons, my white background sometimes comes out looking slightly grey.

Is there a way to whiten the background without interfering with the colour of the subject? I could just up the white level etc. but that would obviously apply to my subject as well.

I have PS and LR but prefer to use LR.

To add some clarity to this post: I am specifically asking about modifying the background colour in lightroom or photoshop whithout it applying to the subject.

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A couple of links that could result useful: zackarias.com/for-photographers/photo-resources/… (it has a problem with the image loading, it worked in the past), and blog.patdavid.net/2013/08/a-simple-headshot-of-myself.html –  Rmano Mar 4 at 17:21

2 Answers 2

You haven't talked about your lighting at all, but that's almost definitely where the problem is. Simply, the background needs to be lit independently of the foreground. You almost definitely need more space between subject and background (to avoid light spill) and depending upon subject size you may need several lights to evenly light the background adequately. Meter for the background and subject independently so that you can be sure enough power is being put out on the background to make it white.

Another problem -- though much smaller -- is likely that using the ColorChecker is working against you. The background is almost definitely not a brilliant pure white, so the color adjustments you're making are helping to bring that down to a more realistic almost-white. Again, lighting the background independently of the foreground helps solve this because you can be sure you're setting the flash output on the background to something that will ensure white is... white.

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I don't know how you can say I almost definitely need more space without know about the lighting conditions. The question was more to do with changing the background colour in post to make minor adjustments without those applying to the subject. I have seen people do it with masks etc. but not sure how to do it. –  connersz Mar 4 at 15:54
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Did you light the subject and background independently? If the answer is no, you almost definitely need more space between the foreground and background in order to adequately light them. That's all there is to it. Your question also doesn't say you can't re-take the photo. –  Dan Wolfgang Mar 4 at 16:35

If the white balance and white point are correct, then the background should be displayed as white. If it isn't, then you are doing something wrong with your color target. If it is a good neutral grey, then the white balance is correct, but the white point is too bright. I would adjust the white point to bring the white point up to where it belongs.

It may also mean that you don't have enough light on the background if the subject has brighter highlights than the background itself (in which case it isn't going to be possible to get a white background without selective color replacement or matte painting). If the subject is more brightly lit than the background, then relatively speaking, the background would be grey.

If the background was too dark and the subject is too bright to bring up the white point overall, then you will need to mask out the subject so you can work exclusively on the background. If it's a fairly regular color, you can probably use the magic select to get a quick starting point. Once you have a mask for the background, you can apply an exposure correction or simply change the color of the background by itself.

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Ya, it sounds more like an exposure issue than a color correction issue. –  rfusca Mar 4 at 14:39
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Yes it is no doubt due to not enough light on the background, but that's hard to get perfect when using the small LCD screen on camera and often looks grey later. –  connersz Mar 4 at 15:23
    
The question is about post processing and adjusting the background colour without changing it for the subject also. –  connersz Mar 4 at 15:56
    
@connersz in that case, masking/matte painting is your only option that I know of. You have to isolate the background from the foreground. –  AJ Henderson Mar 4 at 16:24
    
@AJHenderson I think he's asking how to mask/paint –  rfusca Mar 4 at 17:27

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