Thursday 29 May 2014

Colour - Grey Card Test (Foliage Canopy)

Typical Forest Birding!

It is May in a northern deciduous woodland.  Birding in the woods is usually more about songs and calls than crippling views and when that warbler, flycatcher or thrush finally pops up it is generally bathed in vivid green, making ID more of a challenge.  

HERE I summarised white balance corrections, including the limitations of manual white balance using just the Kelvin colour temperature scale, versus a Grey Card, which can correct for all colour casts, including the green channel.  I also unveiled a "pimped up" grey card rig.  Now to put this rig to the test in the field.

Here is the setting, a typical woodland scene in Ireland in May - pretty green!

Here is the test rig shot without white balance correction.

Now here is that shot again with DNG profile and white balance correction completed - that's just two mouse clicks!

White balance involved shifts in both the Colour Temperature (Red and Blue channels) and in what Adobe refers to as "Tint" (the green channel).  Despite an incredibly overwhelming green cast, white balance was a doddle.

Here is a breakdown of the white balance correction in Camera Raw.  First Colour Temperature.

Colour temperature is reading 5050K.  The yellow component of the foliage has been removed but the green channel is unaffected by the colour temperature correction.  As explained HERE manual white balance tools often don't allow for corrections in the green channel.  Grey card corrections however do correct all channels.

Here, a massive correction in the green channel (Tint +77) was required to bring white balance in line.

The purpose of the rig is for a more in depth view so here is the analysis bit.

Overall the white balance performed really well in this setting.  There is very little if any residual colour casting evident in any of the targets.  There is a slight green cast still evident in the shadows (residual foliage influence) and a slight blue cast evident in the highlights (sky influence). 

In summary, I think it is a very good idea to carry a Grey Card into the forest!

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