The Portland Metro Photographic News

Editor's Note:  If you are serious about Color Balance, and your photography business depends on your ability to produce accurate color images, Steve Anchell provides this technical discussion that you need to digest.  Steve is a respected Oregon photographer, workshop instructor and a PMPN favorite contributor.  Steve has written this primer to help photographers understand the intricacies of achieving accurate color balance.

With all the controls found in digital cameras and in Photoshop it should be easy to achieve good color balance.  In the best of all possible worlds it would seem as if the answer would be to use the white balance presets which are found on most DSLRs.  These presets are set according to the manufacturer’s idea of what will look good and may, or may not, improve the overall color.  For example, the cloud and the thunderbolt both cause the image color to be warmer (how warm is determined by the camera company).  This may, or may not, be an improvement but it is not correct color balance.

In this article I am going to divide color balance into “best” and “accurate.”  Best color is entirely subjective.  If you are working on your own project the best color is anything you like in your image.  If you like the warmer colors of the flash or cloud pre-sets then that is the best color–for you.  If you decide to use the white balance controls in Photoshop to make the photo cooler, that is the best color–for you.

For the professional photographer “best” color is not good enough.  To understand why watch the movie “The Devil Wears Prada.”  In just one short scene you will find out how important it is to accurately reproduce color.  That is the scene where magazine editor, Miranda Priestly (Meryl Streep), is explaining the color of a sweater to her assistant, Andy Sachs (Anne Hathaway).  The sweater is cerulean blue, and if your client has hired you to photograph that sweater for an ad or a catalog it had better reproduce as cerulean blue, I’ll let Miranda explain why in the movie.

And it is not just fashion photography that requires color to be accurate.  Interior designers and architects demand that the color of their walls and furniture selection be spot on.  Toy makers, appliance manufacturers, and most other clients all want the color they specified for their product, not whatever comes out of your camera.  

Standards

In order to reproduce color accurately there must be a standard against which to measure our materials and results.  Sometimes standards can be arbitrary.  For example, were you to chose to use 6500K as your standard this would be an arbitrary choice based on what you, or your client, feels is best color.

Though you may read on the web anything from 5000K to 6500K, 5500K has always been the standard used for determining accurate color in photography.  This is the only color temperature that is entirely neutral.  That means it will reproduce white and gray without a color cast.  

Whatever color temperature you choose as your standard I recommend that the first image in any important series of photographs should include an X-Rite Gray Balance Card or ColorChecker.  I have two ColorCheckers, one is full-sized which is for use in my studio and the other is a Mini ColorChecker which is the size of a credit card and fits in a shirt pocket.

Accurate Color

To reproduce color accurately it is necessary to match the camera and the lights to a specific color temperature as measured in Kelvin (K).  That means if the light source is 2720K and you are using film balanced for 3200K you will need a blue color correction filter (CC) over the lens or a blue light balancing filter (LB) over the lights to bring the two into balance.  If you are using digital you can use the Kelvin white balance adjustment found on high end DSLRs to dial in 2700K and make your final adjustments in Photoshop.  (I chose the 2720K temperature as an example because it is the color of my tungsten lights, see Figure 1).

Figure 1.  This photo was lit using tungsten modeling lights.  The Sekonic Prodigi C-500R color meter read the color temperature as 2720K.  The white balance Kelvin preset (K) on the Nikon D700 was set to 2700K and 20K more was added in Photoshop.  An X-rite ColorChecker is being held by the model, Molly.

From the above it is clear that to achieve accurate color you need to know the color of your lights.  In some instances the color balance is known within a reasonable degree, for example if you are using fairly new 3400K BBA photofloods or 5500K studio strobes.  But if the light is mixed for example, 4100K cool white fluorescent in the ceiling, 6500K daylight coming through a picture window and perhaps a 250W 3200K ECA photoflood as an accent light off to one side, then how do you know the true color temperature of your lights?  In addition the color temperature of photofloods change over time.  The same is true with studio strobes, though to a lesser extent.  In any case the only way to know the true color of your light is to use a color meter.

Why is this important?  Is it not possible to use the RAW image editing capabilities in Photoshop or similar image editing program, to correct the color temperature?  The answer is both yes and no.  You can, and should, make the final adjustment to color balance in a RAW processor but you cannot make it accurate unless you know the color of your light source.  Without knowing the color temperature of the lights you are working in “best” color not “accurate” color.

The reason we use Photoshop for the final color adjustment is because the Kelvin WB presets vary according to the camera–no two necessarily agree.  So we need to rely upon our software to provide a standard available to everyone.  With RAW as your in-camera quality setting, you can use AWB or Kelvin preset or a custom WB preset and then make your final correction in your preferred RAW processing program.

For any of this to have validity it is critical to keep your monitor calibrated by using a Datacolor Spyder3 Pro or similar calibration tool.  I suggest that you calibrate all the way through to your printer using the Studio version of the Spyder3 Pro.

Achieving Accurate Color with a Meter

Let me start with an example.  Without knowing the color temperature of your tungsten lights you set AWB on your camera and expose.  Opening the image in Photoshop you find the color balance chosen by the camera is 3400K (Figure 2).  The color looks good, you might even consider it to be “best” color–that color which you think looks good.  But it will not be accurate.  On the other hand, if you read the light source with a color meter and know that it is 2720K you can open the image in an image editing program and adjust the temperature slider to 2720K.  The meter will also suggest magenta and green filtration for complete color correction.  These can also be added in the image editing program.

Figure 2.  Using the same lighting set-up as in Figure 1 the Nikon D700 was set on AWB.  The results were a color temperature of 3400K, warmer than Figure 1.

The color meter I recommend for anyone making a living photographing for others, is the Sekonic Prodigi C-500R (Figure 3).  The Prodigi C-500R meter uses four color sensors to accurately read either film or digital.  The reason for the differentiation is that digital capture is based on human visual response while film capture is based on the color characteristics of the film being used.  The fourth sensor is required to accurately read human visual response.

Figure 3.  Using White Lightning studio strobes the Sekonic Prodigi C-500R indicates that a -7 blue filter is needed over the lights to bring the color temperature from 5350K to 5500K.  The difference is negligible but may be important, depending on how accurate you need to be.

All that a color meter will do for you is read the color of your light source so that you can match it to your film or digital WB.  That’s it.  But if you want your color to be accurate you need a color meter.  Even so, no color meter is 100% accurate, but it is as close as you can get.

Using a Prodigi C-500R color meter my strobes register as 5330K.  Using the AWB setting the color temperature is 4200K in Adobe Lightroom (Figure 4).  Using the flash preset it is 6150K in Lightroom (Figure 5).  Knowing the color temperature to be 5560K WB preset in the Nikon D700 to get as close as possible in the camera.  The result is 5300K out of the camera.  The final 30K was added in Lightroom (Figure 6) for a very accurate color rendition.

Figure 4.  Still using strobe lighting the D700 was set on AWB.  The result is a color temperature of 4200K.  This indicates a mired shift of 52 from the 5350K of the strobes resulting in a noticeable blue cast.

Figure 5.  This time the flash preset was used.  The result is a color temperature of 6150K, considerably warmer.  You should be able to discern a pink color cast to the second white patch in from the lower camera left corner.

Figure 6.  The Prodigi meter reads the color temperature of my strobes as 5330K.  The Kelvin preset on the Nikon D700 was set to 5560K which resulted in 5300K in Adobe Lightroom.  This is because the D700 recorded the color temperature at about 250K less than the camera's K preset suggests.  An additional 30K was added in Lightroom.  This is the most natural and accurate of all the images.

Accurate Color without a Meter

If you want your colors to be consistently accurate as possible without using a color meter, then use the following two step process.

1. Set the custom white balance in your camera using a gray card.  A neutral gray card should be used to obtain accurate white balance with DSLRs while a white card should be used for video.
2. After you have set the custom white balance using a gray card take the first photo with an X-Rite Gray Scale Balance Card.  After downloading your images into an image editing program use the dropper tool to set the white and black points using the reference card image.  Once these are set determine accurate color temperature by using the gray strip in the middle.

If you follow this procedure your color balance will be as near to accurate as possible without using a color meter.

Sources

Sekonic Light Meters, (914) 347-3300

X-Rite, (800) 248-9748

Steve Anchell is a writer and photographer who teaches darkroom and digital workshops from his home in Salem, Oregon. He will be teaching one day Lightroom Library and Lightroom Develop workshops on February 20 and 27.  For more information visit www.anchellworkshops.com.

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First printed in Shutterbug Expert Photo Techniques 2009/2010

Updated for Portland Metro Photographic News