[Robert N]

When setting the manual white balance on the K-3, the instruction manual advises selecting a white item for colour balance reference. However, when trying both white and grey test cards, the grey card appears to give a more consistent result, when comparing the adjusted balance to the equivalent photoshop adjusted balance (using a grey test card). Hence on this basis, I would have thought Pentax would advocate using a grey test card, rather than white. Although I appreciate that generally, it is easier to find a white item than grey, I would expect Pentax to advocate a grey card for best results. I have both white and grey credit card sized test cards.
It will interesting to see what others users feel on this subject.

[photoptimist]

Good advice!

One issue with "white" paper is that it often contains optical brighteners (Wikipedia). These additives convert UV light into a blueish glow that tricks the human eye into seeing a brighter white. Anyone who has seen a t-shirt glow intensely under a blacklight has seen what these can do. Brighteners are also added to textiles and laundry detergents to make yellowed clothing look whiter than it really is. Needless to say, anything with optical brighteners in it will give weird white balance reading.

A gray card also has the distinct advantage of being the right target light meter readings.

[stevebrot]

I would expect Pentax to advocate a grey card for best results

I would think so as well and that would be my recommendation. My reasoning goes as follows:

• As noted above, white paper often has brighteners. The same is true for white fabrics that have been laundered. In addition, white objects are often not white in the colorimetric sense (equal contributions of red, green, and blue).
• Commercially available 18% gray cards do have equal contribution of red, green, and blue and will provide an unambiguous reference
• Post-processing software (e.g. Adobe Lightroom), may not allow "dropper select" of a high value white point as white balance reference

I carry a gray card for potentially tricky stage or event lighting and try to include it (held by a willing volunteer) in test shots for various positions in the room or stage. As for in-camera settings, I use auto, multi-auto, or a setting of 5500°K, shooting RAW, with intent to edit WB as needed later in post.

As for the advice in the user manual...I suspect the suggestion of white is a matter of convenience.


Steve

[TonyW]

As long as the white balance card is accurate in equal RGB it should not really matter if it is light or mid grey. Be aware that some 18% grey cards are not actually neutral (they do not need to be as they are designed for exposure estimation). Note: I have not looked at 18% reflective cards other than those produced by Kodak which do exhibit colour variation, my own being towards the warm side of neutral

See attached. Left to right Kodak Gray Card, X- Rite Colour Checker Passport, Lastolite 12% Ezybalance. The X Rite passport also has a white balance and grey card built in. Using white balance on the Kodak card produces too blue an image, but really only a small difference that can easily be accounted for if needed

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Last edited by TonyW; 02-04-2020 at 06:10 AM.