Hey tweets, I've been following the discussion about the golden-plover
ID with great interest, partly because it is about how we humans
perceive color. This is a big issue in science and technology and has
been a big part of my professional life for many years. As a print
production consultant with more than 30 years of printing and color
separating experience, I would like to offer some things to consider
when using color as a field mark in photos:

1. Every person perceives color slightly differently. What looks
reddish to some might look yellowish to another. Furthermore, our
color perception changes with age: older people tend to see more
yellow. (If you'd like to check out how perceptive your eyes are to
minor changes in tone, take the color test at http://www.xrite.com/custom_page.aspx?pageid=77&lang=en
and see how well you score.)

2. Every computer monitor displays color slightly differently, unless
the monitors have been color-calibrated to the same standard. Color-
calibrating a monitor is a complicated technical process (magazines
that desire to color-calibrate their entire production system have
been known to pay an expert as much as $10,000.00 for this service).
As a result, what looks yellowish on one monitor can look bluish on
another.

3. Monitors display color using discrete pixels of emitted light. The
pixels are created (on my liquid crystal screen at least) by dyes that
show RGB light. The dyes are limited in their gamut (range of colors).
The gamut emitted by a computer screen is also limited by the amount
of back light it uses. Screens can be set to be very bright or not so
bright, changing the colors they display. Nature displays color by
absorbing some wavelengths of light and reflecting others. Colors in
nature can only be seen in sunlight, whereas colors on a monitor can
be seen when it's dark. Because of these limitations and differences,
a monitor's colors are not a perfect match for nature's colors. (If
you want to read more about color gamut, check out the Wikipedia
article "Gamut" and references in it.)

4. Different software apps address Problem #3 differently. You can see
this for yourself if you take the same photo and open it in:
PhotoShop, Adobe Reader, iPhoto, Adobe Acrobat, and Preview. The photo
looks slightly different in each app.

5. I don't know very much about digital cameras, but I suspect that
they must make compromises between the natural spectrum and the color
gamut, just as monitors must.

6. Since the colors we see are wavelengths of light, they can vary
depending on the angle at which they arrive to shine upon an object
and also the angle at which they leave an object to reach our eyes or
a camera. Ambient light also depends on how the surroundings reflect
or scatter light. Ambient light is thus very changeable, making it
difficult to compare one photo to another when the photos are taken at
different times and under different conditions.

7. Midtone colors (ones made up of almost-equal amounts of red/green/
blue light) are especially sensitive to factors 2-6 because slight
differences in any one of the RGB components can sway the midtone
disproportionately toward R or G or B, making the overall tone change
significantly. Browns are midtone colors.

8. The human eye is deeply influenced by ambience, seeing colors that
either aren't there at all, or are different than we perceive. To see
how this works, check out the TED lecture on YouTube: Don't Believe
Your Lying Eyes.

The conclusion I reach from all the above is that we should be very
careful about using colors as definitive field marks when differences
between one species and another are slight, when there is overlap
among individual birds, and when you are trying to identify a bird in
isolation from other members of the same species or other members of
related species. - Connie, Seattle

constancesidles at gmail.com
www.constancypress.com



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