HCT User Guide
page 26
Copyright © 2001 HutchColor, LLC
User_Guide_43.docx 2/10/19
Adjusting profiling curve, exposure and balance
The camera curve, exposure and balance used when creating a profile should be determined
together, as they can affect each other. Each camera software is different but the following steps are
a good guide for most cameras. If your camera has no capture software, make a series of
exposures or exports (if you have the ability to alter the file during export) until you get a file that
meets the following criteria as closely as possible.
•
To ensure the basic curve has a sufficiently wide sensitivity range, place a black trap in the
scene with the target to simulate the darkest black the camera is likely to encounter. A good
black trap can be made by lining a black plastic 35mm film canister (remember film?) with black
felt. Make sure no direct light falls inside the canister.
•
If your camera software displays a curve over a histogram, start with a curve wide enough to
include both the blackest and whitest regions of the HCT (including black trap) simultaneously. If
necessary, edit a basic curve to extend the range as needed.
•
Set the optimum exposure by adjusting aperture, integration time, ISO sensitivity and/or light
intensity until the brightest white patch of the target reads about 245-250 in all three colors.
•
When possible, always profile and shoot at the lowest ISO setting to reduce noise. In some
cases it may be desirable to create different profiles for different ISO settings.
•
Adjust the shadow end of the curve until the black trap reads between 2 and 10 in all channels.
If the black trap consistently reads 0, at least try to get the darkest patch of the HCT (patch V28)
above 0 in all channels. If possible, make sure the camera curve has at least an 8 f-stop range
from white to black (may not be possible on some cameras.)
•
Tweak the curve until it is almost a straight line with roughly equal separation throughout the
scale but slightly less contrast in shadows.
•
Adjust overall curve height at the middle tone until patch L27 on the HCT measures somewhere
between 100 and 130 in all colors.
•
Balance may be set one of two ways. If there is no metamerism error between the target
material and the standard gray card you will use during production work, use the gray card to
balance the profiling exposure. If the target takes on a color cast due to metamerism failure or
UV or IR reflection, balance on a neutral gray or white patch of the TARGET for the profile
exposure but use the standard GRAY CARD during production work.
Using the profile
There are two primary uses for a camera profile: to display the image correctly in the camera
software or image editing software like Photoshop, and to ensure a good reproduction on an output
device.
Most medium-format camera software will allow you to select your own profile to be used during
framing and capture. Generally this is set in the Preferences under a heading like “Profiles” or ICC”.
For this to be effective you also need a good monitor profile. What you see on the monitor at the
time of capture should now be a good simulation of the original, except in very saturated colors that
may be outside the monitor’s gamut. Remember that the appearance on your monitor will be greatly
affected by the intensity and color temperature of the ambient lighting.
Some camera software will allow you to embed the profile in a ‘raw’ RGB capture. This is ideal if you
want to preserve the maximum quality in a high-bit file, yet maintain the integrity offered by the
profile. Always make sure the recipient or output process is ICC-aware and knows how to use the
camera profile correctly.
Some camera software will convert from your selected camera profile into a ‘working space’ of your
choice when the file is saved or exported. If the final destination is a commercial press or wide-
