Color Balance Facts

Most professional studio photoflash units produce a "color temperature" between 5000°K and 6000°K. However, choosing the "correct" color temperature alone does not assure fully accurate color rendition and neutral colors in a scene will still show slight colorcasts, or deviations from true neutral. While it is the nature of Xenon flashtubes to produce excellent color rendition, there remain small discrepancies in the Xenon flash spectrum that require post processing (in Photoshop or "RAW") if perfect color balance and accurate neutrals are to be achieved. This is also true of "color corrected" or "UV coated" flashtubes. Fortunately, with digital equipment, this easily accomplished.

The accessories used, as well as the shooting environment, are usually of more concern than the color temperature of the light source itself. Light modifiers such as umbrellas and softboxes will often change the color balance of the light by as much as 600°K, as will the room colors - even if they appear to the eye to be neutral. These, too, can be easily corrected in Photoshop or RAW.

With the exception of certain very expensive "constant color" lighting equipment, studio flash units that employ variable output power typically vary in color temperature by about 400°K as they are adjusted from Full Power down to 1/32 Power. The flash duration will also vary over this power range, typically becoming about twice as long at the lowest power than at the highest power. However, even the use of these "constant color" lights will not eliminate the effects of accessories and environments.

Recent tests of the ABR800 ringflash with standard reflector, using Gossen Color Pro 3F meter, returned the following results: (previous tests using Minolta Color Meter yielded readings approximately 200°K lower)

At Full Power = 5700°K

At 1/4 Power = 5500°K

At 1/32 Power = 5300°K

The same tests using a production AB800 studio flash returned the following results:

At Full Power = 5850°K

At 1/4 Power = 5650°K

At 1/32 Power = 5450°K

For all but the most critical work, the approximate 150°K difference between the AB and ABR units is insignificant.

However, when flash units are mixed with different accessories it is rare that perfect or consistent color balance will be achieved in the camera unless a "custom white balance" procedure is performed. See the camera instructions for how to do this.

There are two other methods to achieve perfect color balance:

1. Shoot test shots in RAW mode, with a known-neutral object (grey card or pure white card or background) included in the scene. Following the test shot, the neutral object can be removed from the scene or, better, placed in a corner of the scene where it can later be cropped out. When the test shots, or real shots, containing a grey card, are opened in a RAW program, it is a simple matter to use the "eyedropper tool" to sample the grey card to achieve a custom white balance. This will calculate a perfect color balance at the grey card regardless of the effect of the power levels, accessories, etc.. If this is done on a test image, the resulting color balance setting can be applied to all shots in a sequence taken at the same power levels and with the same accessories. Since it is common in a photo session to change power levels and accessories, the preferred method is to include a grey card in each shot when possible.

2. A similar procedure may be accomplished directly in Photoshop when shooting either JPG or uncompressed modes.

Shoot the session using either the "Flash" or "Daylight" white balance modes or, preferably, using a "custom white balance" procedure, including a grey card in at least one image.

Open the images in Photoshop using the same color space (sRGB or Adobe RGB98) as was set in the camera.

Open a "Levels" adjustment layer. Select the center "eyedropper tool" (grey balance) and place it over the grey card in the image and click. This will automatically adjust the Red, Blue and Green "Gamma" to produce a perfect neutral color at the point sampled. The results of this custom levels adjustment can be saved as a preset if desired and quickly be applied to other images in the same session. Once again, it is good practice to include a grey card in each image when possible so that any changes in power levels or accessories can be compensated for. In this same adjustment layer you can adjust the overall white point, black point and Gamma to achieve the contrast and tonal range desired for each shot

For sessions using a white or neutral gray seamless background it is possible to omit the inclusion of a grey card and to merely use the background as the neutral grey object. A word of caution though: Whether using a grey card or neutral background it is very important that the object be truly neutral because there are many shades of grey (blue-grey, green-grey, etc. The same applies to "white paper". So a photo grey card is the most accurate. If the grey object is not truly neutral any of the above the color correcting procedures will render it neutral and, as a result, will inaccurately render all other objects in the scene.