The
purpose of a digital camera chart is to characterise the camera in
the lighting conditions being used.
The chart is photographed in the
lighting conditions used and a profile is made by comparing the camera
RGB colours with the CIE colours of the chart as measured in manufacturing.
It is then critical that the chart looks the same in the photograph
as when it was measured. This means there should not be any gloss effects
where light from the source is directly reflected back into the camera.
To aid the photographer with this we do not have any gloss patches
in the chart and the chart is made from very matte paper.
Some charts
have gloss patches and even silken patches where small amount of gloss
effect
are seen, almost imperceptible to the user but the software can easily
detect it.
Not only do we use matte paper to eliminate gloss effects
but we print the chart with colour fast inks so, if treated with care
the chart
will last a long time.
To increase the range of the chart so shadow
areas are handled correctly we have attached flock patches which
make the chart much darker than any matte print process can deliver.
The chart comes in two sections.
One covers the
whole area and is a randomised chart area which reduces the problems
of the illumination being none uniform not only in light level but
also in colour.
If for instance you have all the green patches on one
side of the chart and that side of the chart was illuminated in darker,
yellowier light then after profiling all the green colours would come
out lighter and bluer because the profiling software will compensate
for all the different light on the green patches.
Having random patches
spreads out the effect of the varying illumination so each colour region
will have some patches from all the illumination conditions on the
chart. Thus the profiling software will balance out the corrections
made and one colour will not be unduly effected by one lighting condition.
There is a second, small chart in the lower
left hand corner.
This is for use in shooting very small field of
view shots; for instance products like perfume bottles.
In this case
you just put the small chart into the field of view without having
to undo your photographic set up just to shoot the chart. Just place
the small chart into the field of view and use the small chart data
set.
Each chart comes with its own data set.
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