Photo Effects (Was Rio Tefe)

[Scot Gillespie <Scot.Gillespie@epsedin.co.uk>]

Mike wise wrote:
.....I feel that Uwe's photo is slightly 'enhanced'. Note the violet cast on
the white part of the tail. It's possible that a magenta filter was put over
the flash or something like that..... 

Photographs in every case always lie. This is down to a whole barrel load of
factors, I will try to cover two.

Colour Temperature: Each light source has a different and usually variable
colour temperature, which dynamically the human eye automatically adjusts
its 'white balance' too (noon daylight is relatively blue, tungsten bulb
light is tannin yellow, and fluorescent light anywhere between turquoise to
magenta). Most video/digital cameras now have an automatic white balance,
which will digitally adjust the relative colour temperature balance. Film
however has a fixed layer structure of colour filters that are set for
either an optimum "daylight" or "tungsten" colour balance. Traditionally,
this is compensated for by the use of a colour temperature meter and a set
of compensatory filters - this is a black art comparable to balancing pH,
unskilled use of additive filters can lead to horrific results. Minor colour
balance correction can be accomplished when prints are made (by a skilled
hand printer), but with slide film you tend to have to get it right first
time.

The colour temperature of the light source is also affected by anything it
is passing through, this is probably accentuated in our case most by waters
rich in tannins, so we have a brown filter between the light source, the
subject, and then film. And we are presuming that the glass of the tank is
having a neutral colour filtering affect - which is not generally true.

The colour temperature can also be affected by any subject it is reflected
off; plants, gravel, a thin coat of algae on the sides an back of the tank
etc.. As Mike pointed out it looks like Uwe used a Magenta filter, with
fluorescent lighting (and no flash) in the photograph on
http://geocities.com/Heartland/Plains/7918/aggriotefe.gif. 
This is one of the 'standard' corrections for fluorescent lighting, but
because of other colour temperature filtering, and reflection, effects this
resulted in a violet colour cast to the subject.

Refraction/reflection: In some fish you can see an iridescence on the body
and fins as they move relative to your eye and the light source, this is
caused by tiny semi-regular ridges which act like tiny prisms separating the
light its individual light sequences something akin to a rainbow. However,
dependant on the spacing, size and regularity of the tiny ridges the effect
can be just like a rainbow, be an enhanced one colour 'tone', or can be
practically unnoticeable to the naked eye. Also as this 'shimmering' effect
is dependant on movement, if the fish is static relative to the eye and
light source the shimmering/iridescent effect is not visible and is only
seen as one colour, as only one sequence of the light enters your eye. 

These latter two points come to a head if a flash is used on the subject.
This 'goes off and on' at a relatively fast speed, far faster than the sync
shutter speed of your camera, and relatively freezes the subject relative to
the camera and the light source. The intensity of the light from the flash
also is far in excess of any natural light the fish would be subject to, and
this intensity is amplifies any iridescent light sequence coming relative to
the ordinary reflected light from the fish. This effect can be best observed
on Dieter Bork's pictures on the Krib
http://www.thekrib.com/Apisto/mayland-book.html.

I think I'll now augment Mikes mantra: Colour photos should not be used in
apisto IDs...;-)

Scot
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