Upload & Sell: On
It can be kind of hard to get your head around ... and most people will think I'm whack as it isn't something they've heard advocated elsewhere.
I'm suggesting that the WB from ambient sunlight is the gradient combination of the warm/cool. The "white" sunlight gets separated by the atmosphere in a gradient range from warm to cool (somewhat like a spherical a prism if you will). When our subject receives light from all of that range simultaneously, it is receiving a re-assembly of the warm & cool back into white ... i.e. daylight balance.
When we take pictures in the shade, the warm direct sunlight is being blocked and only the cool overhead sky is available to illuminate our subject, thus our WB is cool. Conversely, during the "golden hour" when our subject is being sidelit from the direct warm light, our sidelit subject is not reflecting the illumination from the overhead sky and our WB is warm.
Thus warm + cool = neutral. This can be seen as Cyan (BG) + Red or Blue + Yellow (RG) if you will.
In many instances, the separation of the warm & cool are reassembled into an homogenous blend of the two and we accept it as a single color of light. However, in the case of your knife, we have a scenario where the diffuse light presents that reassembling of warm & cool, yet the angle of the knife and its subsequent AI=AR is reflecting a particular portion of the overhead sky. That particular portion of the sky is absent of the warm light contribution to the overall homogenized WB.
This can be evidenced by how the changes in the knife's angle changes the color of the knife, while the unchanged items in the scene remain the same. Only the knife is changing color, because it is reflecting a different color of light that is illuminating it. This can even be seen within the same image with the changing color of the knife's spine.
It isn't quite as though you have two different light sources as we would typically think of say one tungsten and one fluorescent mixture, but more of a blended gradient.
Like I said, many will think this is whack, but it is what gives us blue snow, blue hair and a myriad of other blue/cyanic tones in our neutrals. Sometimes the separation of the warm and cool works well to our advantage, i.e. a cool blue body of water reflecting the cool overhead sky. Change the angle of the reflection to include equal amounts of diffuse blue overhead and specular warm and the offset each other to a neutral and our water looks dull gray. Change the angle even further toward the specular warm light and we get the warm golden tones. The body of water didn't change colors, only the angle of light that we are reflecting iaw AI=AR.
While this isn't something that most people concern themselves with, it is something that I am (insert OCD comment now ) aware of that bothered me for a long time regarding it, until I better came to understand rgb light theory and this separation/re-assembly that represents (daylight) ambient light as a blending of diffuse cool and direct warm in varying degree/amount iaw AI=AR.
One additional aspect regarding this. When we have "gray skies", we typically associate that 'gray' to a reduction in luminance, but it is also a very homogenized blending of the the warm & cool to produce the neutral "gray" lighting. Blue bark in the forest while golden shafts of light filter through the canopy is yet another indication of how ambient white is separated into warm & cool relative to our orientation to a given portion of the sky.
Now that you (et al) think I'm totally nuts ...
Short version (i.e. practical vs. theory) ... +1 @ tweak on the blue channel.
How much you take out vs. leave in, highly subjective to what you deem looks "natural", and what kind of mood you want to present.
The reason I mention it here ... is that the mood for me at the image is one of "old world Tuscany" kind of thing and the associated warmth. Imo, having such blue is incongruous with a warm (or neutral) mood. Yeah, its a nit ... but that's what you came here for.
I still like it.
Edited on Mar 04, 2013 at 04:06 PM · View previous versions