The light tent, and understanding white balance

Several weeks ago I had an email from a lady called Gwen Hartley who had read my articles about my self-assembled light tent (parts 1, 2, 3) but was having some issues with the colour of the images that came out. I’m reproducing our correspondence with her permission, as I think this is useful information.

Gwen wrote:

… all the pictures we take (without flash, right?) are YELLOW & people cannot see the true color of my husband’s artwork (he’s a glassblower).

… We’re currently using a larger, taller lightbox, as he needed to be able to put taller pieces in it to photograph for customers. We have 11 lights now — with 100 watt compact fluorescents in them, and they STILL look yellow & are not a true reflection of the piece’s color.

I attached 2 pics of the pieces we took yesterday… notice how YELLOW they look?! We even tried to brighten them in PhotoImpact… NO LUCK! What are we doing wrong? We are supposed to NOT use a flash, right, so we don’t get the light spot? It looks SUPER bright to the eye, but when we photograph it — it’s YELLOW.

IMG_8002.jpg    IMG_8007.jpg

At this stage I didn’t really have enough information make a definite diagnosis, but I thought it would be a good idea to work through the problem with her:

What kind of camera are you using to take the photos?

You need to set your white balance to compensate for the lighting conditions. If you are using a DSLR you can usually shoot in RAW and then change the white balance in your photo software. For a compact, sometimes they have an “indoor” or “tungsten / fluorescent” light setting… otherwise you can use some software to set the neutral colour – I’m not familiar with PhotoImpact though.

I use software called Lightroom which is intended for DSLR users primarily… by using the eyedropper white balance tool and tweaking the brightness and clarity / contrast settings the images look a little better to me.

Again, I don’t know enough about your specific situation, but basically you want to work out the colour temperature of the lamps you are using and compensate for it – lots of photo software has white balance or neutral balance tools – you just click on the bit of the image you know is white, and it rebalances the image for you.

I also attached some edited versions of the images she had sent me, which looked like this:

IMG_8002.jpg    IMG_8007.jpg

Gwen was pleased at the changes:

[we have a] Canon PowerShot S2 IS – 5 megapixels… I don’t need anything fancy – just TRUE COLORS of the pieces & non-yellow-looking images!

… I’ll check into the white balance… there HAS to be something on one of the many settings on this camera!

Now, luckily, if you don’t have a DSLR then something like a PowerShot S2 is just the kind of compact camera you’d want for this kind of photography, as it has the right level of manual control to allow adjustment of white balance etc.. I did a bit of research, and came up with the following advice:

A PowerShot is a nice flexible compact camera.

Looking into the details about the camera you have, I found this review.

It looks like if you set the camera to P or Av mode, and then go into the function menu, the second option down will be White Balance – try the Tungsten and Flourescent light settings (if you have the manual for the camera you’ll probably be able to learn more about this). That would help for getting the right colours straight off the camera. Custom WB would be even better, in this mode you usually photograph something you know to be white, and then tell the camera to use that as a marker to where the white is in the image.

I also did some reading up on the software you have, PhotoImpact, and I found this. This describes doing basically what I did with your other images – you get an eyedropper to pick a colour from the image that should be “white”, or the software can try to fix it in Auto mode.

I have to say that Gwen’s husband Scott does produce some truly beautiful artwork – check out Infinity Art Glass to take a look. I’m really glad to have been able to help them.

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5 responses to “The light tent, and understanding white balance

  1. Wow, incredible glass work… I too have problems with white balance when I take pictures (sometime), but I tend to do a lot snap shots out doors. I am hoping to start using Photoshop CS4 to improve my handy work.

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  2. Glass is one of the toughest things to light and photograph well. The work looks amazing so I hope they find a system that they like.

    I used to do a lot of this kind of work so here’s my USD$0.02 worth…

    1) Skip the CFL bulbs and use color balanced photo bulbs. Assuming they still sell these. They will get you as close as possible to full spectrum white light. Problem with most CFL is not so much that they are heavy on green but more that they are almost completely lacking in some of the other spectra. So it’s tough to correct after the fact because you can dial down the green but tough to add in the missing spectra. If I *had* to use CFL, I’d at least buy full-spectrum versions such as plant grow lights or reptile lights.

    2) Whether they switch bulbs or not, use the white card method. Photo stores used to sell reference white cards but a piece of clean poster board is a good approximation. Hold it in the spot where the object being photographed will rest and turn on the lights. Next hold the camera so the card completely fills the screen and use the Custom White Balance. This will tell the camera what “white” should be and all the other colors will use it as a reference. This is much more accurate than the pre-sets in most cases. This should be done fresh for every shoot because bulbs change character as they accumulate burn time. This process will get the original image file as close as possible to correctly balanced and so require much less post-processing.

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  3. This is a great summary of things to try to correct for dodgy WB Andy.

    Canon, for all their various achievements (and I’m a fan remember) have never really nailed auto WB in artificial light, be it tungsten or fluorescent.
    When shooting with a light tent I always use a custom WB set from a white card image. Here’s a useful tip though – if you’re shooting with CFLs particularly, make sure they’ve had time to completely warm up before setting the white balance, or you might find you still need to correct later.

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  4. If you want to be pickier you need to start understanding color spaces, making sure you have color profiles for your monitor, printer, etc. Correcting the white balance is theoretically only useful if your monitor has a colour profile (at least, once you then try to reproduce it elsewhere). I’ve dabbled with this but I’m not going to claim to know enough to speak authoritatively. Nevertheless, this FAQ is pretty thorough: http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html.

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  5. Having read your post and Nick’s post too, I think I’ll be making efforts into constructing my own tent soon…

    Looking for advice and hints/tips as to what works well? Particularly whether to use tracing paper or material for the diffuser? What type and how many lights to use? And if you’ve seen any foldable designs I might be able to plagiarise?

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