Calibrating
the ProgRes 3012 Digital Camera
by Stephen Seiberling
The following instructions
reflect the results of informal experimentation over the course of
several months with the ProgRes 3012 digital camera in the University
of North Carolina Herbarium. Helpful advice provided by Gene Hammond
of Catalist, Inc. in Greensboro, NC, and Steve Davis of the UNC Chapel
Hill Anthropology Dept., along with information contained in the ProgRes
Plugin user's manual (Release 3.x, June 1996), were also very useful
in developing these procedures.
Piezo Calibration
Piezo
calibration causes the camera to make minute adjustments to the devices
that control its light sensors in order to minimize certain types
of distortion in captured images. It may be necessary to perform this
step if the camera is jostled in any way, as is likely to occur should
it be removed from the copy stand, if the ProgRes Plugin software
is reinstalled, or simply after several months of normal use.
The need for piezo calibration can be checked
by comparing the three RGB channels of a recently captured image in
Photoshop. While viewing the image, shift between the red, green and
blue channels by pressing CTRL 1, CTRL 2 or CTRL 3. (CTRL ~ restores
the image to all three color channels.) A clearly noticeable shift
in the position of the image while changing from one color channel
to another is an indication that the camera's light sensors are no
longer properly calibrated, requiring execution of the steps listed
below. (Other forms of image distortion may also be caused by the
need for recalibration.)
The
following steps assume the camera is mounted on the Bogen System 800
copy stand as described in the document titled Capturing and Processing
Digital Images of Plant Specimens in the University of North Carolina
Herbarium under System Description. Additional information
on piezo calibration may be found in the ProgRes Plugin user's manual
(Release 3.x, June 1996), pp. 1-12 to 1-17 and pp. 3-30 to 3-33, and
in the plugin online Help files.
Step 1. Remove
the lens from the ProgRes 3012 camera storing it in a safe, dust free
location (e.g. inside the calibration tube container) and attach the
calibration tube by screwing it into the camera in place of the lens.
Step 2. Place
a large sheet of white paper on the surface of the table. The glass
surface of the copy stand is very reflective and may interfere with
successful camera calibration. (If you only have an 8½ x 11
sheet of white paper, lower the level of the camera so that the paper
fully occupies the field of view of the camera with the normal lens
in place.)
Step 3. Turn
on the camera using the green switch on the power supply.
Step 4. Open
Photoshop. Select File>Import>ProgRes_v.4.01.
Step 5. It may
to be helpful to restore the main settings of the plugin software
to their default conditions before carrying out piezo calibration.
Click on the Balance... button, click on Load..., and
open bal0.tac to restore the color balance settings. Click Ok
in the Colour Balance window to return to the main plugin window.
(This may also be done simply by clicking the Reset button
in the ProgRes plugin main window.) Click the Configure...
button, Load... and open config0.con to restore the configuration
settings to their defaults. Click Ok in the Configuration window
to return to the main plugin window. Make sure the Exposure time is
set to 1 and that the Overexposure box is checked in the main window.
Step 6. Turn
on the copy stand lights and turn off the room overhead lights. Raise
the brightness level of the copy stand lights until the image displayed
in the plugin window becomes light green (the overexposure indication),
and then lower the lighting intensity until the "false"
green just disappears.
Step 7. Click
on the Camera… button.
Step 8. The Camera
Setup window will now appear. Check to make sure that the number in
the Camera Label box corresponds to the camera's serial number, which
may be found on the back of the camera and on the camera's power supply
box. Select an Exposure time of x1. Make sure that the Threshold is
set to 0.15, and that Iterations is set to 10.
Step 9. Check
the box for 512 x 387 Image Format (the smallest resolution). Make
sure that none of the boxes for any other Image Format are checked.
Click on the Start Calibration button. A small popup window
will now appear instructing you to set up a slightly defocused checkerboard.
(The calibration tube, which should be attached to the camera at this
point, is designed to provide the appropriate image.) Click on OK.
Step 10. Evaluate
the results which will appear in the Camera Setup window for the 512
x 387 format based on the following criteria: Both the X and Y measurements
should be no more than 0.03 um. apart (for example, values should
be closer than 0.09 and 0.13); Neither
value should be above 0.14 um.
Step 11. If one or both of the above criteria are not met for the
first calibration at 512 x 387, repeat steps 9 & 10 until appropriate
values are obtained.
Step 12. Once suitable values have been produced at the 512 x 387
resolution, check the All box to select all eight of the Image Format
resolutions at once. Click on the Start Calibration button,
and click OK in the small popup window.
Step 13. Evaluate the results for all eight Image Format resolutions
using the same criteria as above, i.e. each pair of numbers should
have a spread no larger than 0.03, and no individual value should
be greater than 0.14. If any values do not meet the criteria, redo
the procedure returning to step 9. (You may find it necessary to repeat
this process two or three times, before all values are acceptable.)
Step 14. Once suitable values are obtained for all Image Format
resolutions at x1 Exposure time, exit the Camera Setup window by clicking
on Ok. If longer exposure times for capturing images may be
used, repeat the process using the following steps. Select an exposure
time of 2 using the Exposure time slider in the lower left portion
of the main ProgRes Plugin window. Readjust the light intensity so
the false green just disappears, and then repeat the above steps 7
through 13 at the Exposure time of x2. This same process should then
be repeated for x3, and x4 exposure times. When values that meet the
two criteria in step 10 have been obtained at all eight Image Format
resolutions, for all four Exposure times, the process is complete.
(The whole process can take an hour or more to fully complete. If
there's no need to capture images at longer exposure times, end the
process after successful calibration at x1.)
Color
Calibration
Once
a particular lighting setup has been established for capturing images
with the ProgRes 3012 camera it is important to calibrate how the
camera will interpret color for those lighting conditions. The results
of the procedure are saved in a color matrix file which can be used
to adjust the output of the camera when capturing images. (In order
to apply the calibration results the appropriate color matrix file
needs to be specified in the ProgRes plugin Configuration window.
See Capturing Images with the ProgRes Camera in the document
titled Capturing and Processing Digital Images of Plant Specimens
in the University of North Carolina Herbarium for more information
about using color matrix files.)
Additional
information on color calibration is contained in the ProgRes plugin
user's manual (Release 3.x, June 1996), pp. 3-35 to 3-36, and may
also be found in the ProgRes plugin Help files.
Step
1. If it is not already on, turn on the camera using the green switch
on the power supply.
Step 2. Open Photoshop and select File>Import>ProgRes_v.4.01.
Step 3. Restore the main settings of the plugin software to their
default conditions by doing the following: Click on the Reset
button in the ProgRes Plugin main window to restore the color balance
settings; Click the Configure... button, Load..., and
open the config0.con file to restore the configuration settings to
their defaults. Before exiting the Configuration window click on the
box for Shading Correction: White and Black so that it is checked.
Click Ok in the Configuration window to return to the main plugin
window.
Step
4. Remove the camera lens cap and position the GretagMacBeth ColorChecker
chart under camera in the center of the location where herbarium sheets
are placed for image capture. Adjust the height of the camera with the
Varispeed 1000 motorized height control mechanism so that the color
checker chart entirely fills the display window from left to right,
but with all of the color squares on the chart still fully visible.
(It may be necessary to turn on the copy stand lights to be able to
see this clearly.) The appropriate height of the camera should be about
84 cm. as indicated by the position of the lower edge of the motorized
height control mechanism on the ruled portion of the copy stand column.
Step 5. Establish the particular lighting conditions used to capture
images. (See Lighting Setup in Capturing and Processing
Digital Images of Plant Specimens in the University of North Carolina
Herbarium for more information about lighting.) Remember to turn
off the room overhead lights. Click on the Start Focus button,
and adjust the lens focal ring until the image is sharply focused.
(See Capturing Images with the ProgRes Camera in Capturing
and Processing Digital Images of Plant Specimens in the University
of North Carolina Herbarium for information about focusing.) Now
readjust the height of the camera if necessary so the color chart
properly fills the display window. Refocus the camera.
Step
6. Temporarily remove the ColorChecker chart and, without changing
the height of the camera, follow the procedures for establishing the
white reference as described under Shading Calibration below.
(After completing color calibration the white reference should then
be reestablished with the camera in its normal position for capturing
herbarium sheet images.)
Step 7. Again place the color chart in the center of the copy stand
table. Rotate the chart so the white field is displayed in the lower
left corner of the ProgRes Plugin display window. Carefully reposition
the chart so that it's centered, with all of the color squares fully
visible, and so that the top and bottom edges of the chart are parallel
to the top and bottom of the display window. (It's helpful to set
the display to 200% when making this adjustment.)
Step 8. Make sure the Overexposure box is checked in the plugin window.
Adjust the aperture ring on the camera lens (the one closest to the
camera body) so that the image is bright, but no part is overexposed
(the "false" green should not be visible). If you have not
already done so, make sure that the box for Shading Correction: White
and Black is checked in the Configuration window of the plugin software.
Step 9. Generate a prescan of the color chart by clicking on the Prescan
button. Now click in the Crop Size box so that a check appears. Adjust
the size of the cropping box by clicking and dragging the corners
of the frame with the right mouse button so that the box extends from
the upper left corner of the dark skin tone square to the lower right
corner of the black square.
Step 10. Click on the Camera…button. In the Camera Setup window
click on the Get Colour Reference… button. Click Start
in the Colour Calibrator window. The ProgRes plugin software now analyzes
the color output of the camera for the lighting conditions based on
the expected values of the squares in the color chart and reports
an average score for the precision attained. Scores of 95.0 or higher
are desirable. Save the results by changing the Matrix File Name to
something that can be recalled later (e.g. ps_test1.mtx) and clicking
on the Save button. (The file name requires the .mtx extension
and should begin with the letters ps.) This saves the data from the
color analysis in a file that is used to adjust image output if it
is specified as the Colour Matrix file in the Configuration window.
Click on the Ok button to exit the Colour Calibrator window.
Click on Ok to close the Camera Setup window.
Shading Calibration
The
ProgRes 3012 camera may be calibrated to adjust for inconsistencies
in the ability of the camera's light sensors to produce a completely
black signal (black reference calibration), and to correct for variation
in lighting intensity across the portion of the copy stand table where
specimens are placed for scanning (white reference calibration). It
is probably unnecessary to redo the black reference calibration for
new lighting conditions, however, results for the white reference
will differ if the lighting setup is modified, and thus will benefit
from recalibration. (In order to use the results from the black and
white reference calibrations make sure that the box for Shading Correction:
White and Black is checked in the Configuration window of the ProgRes
plugin software.)
Prior
to carrying out black and white shading calibration it may be helpful
to restore the color balance settings to their default values by clicking
on the Reset button in the ProgRes Plugin main window. Also
be sure to select the appropriate Colour Matrix file established for
the current lighting setup in the plugin Configuration window (see
Color Calibration, above) before carrying out the following
steps.
Additional
information on black and white shading calibration may be found in
the ProgRes plugin user's manual (Release 3.x, June 1996), pp. 3-37
to 3?38, and in the ProgRes plugin Help files.
Black
Reference
Step
1. Turn on the camera using the green switch on the power supply.
Step
2. Open Photoshop. Select File>Import>ProgRes_v.4.01.
Step 3. Make sure the lens cap is screwed on all the way. Turn off
all lights in the room.
Step 4. Click on the Camera…button in the ProgRes Plugin window.
Step 5. Click Get Black Reference in the Camera Setup window.
Click on Yes in the Global Black Reference window. The camera
now performs a scan to calibrate it's light sensors to a totally black
image. Once the scan is complete it's safe to turn the lights back
on.
Step 6. Click on Ok in the Camera Setup window to exit.
White
Reference
Step
1. Position a large, clean, white sheet of paper on the surface of the
copy stand table. The sheet of paper should be larger than an herbarium
sheet so that it covers the entire area scanned by the camera. If there
are any visible marks or other blemishes on the side of the paper facing
the lens when the calibration is performed, subsequently scanned images
using white shading correction will contain areas of distortion.
Step 2. Make sure the camera height is set to the level used to capture
herbarium specimen images (normally about 126 cm. as indicated by
the position of the lower edge of the motorized height control mechanism
on the copy stand column.), unless establishing a white reference
for color calibration (see Step 6 under Color Calibration,
above).
Step 3. Turn on the camera using the green switch on the power supply.
Step 4. Open Photoshop. Select File>Import>ProgRes_v.4.01.
Step 5. Establish the precise lighting conditions used to capture
images. (See Lighting Setup in Capturing and Processing
Digital Images of Plant Specimens in the University of North Carolina
Herbarium for more information about lighting.)
Step 6. Make sure the Overexposure box is checked in the ProgRes Plugin
window. Remove the camera lens cap. Adjust the lens aperture ring
until the "false" green appears, then turn the ring clockwise
to decrease the aperture until the green just disappears. The aperture
setting should be close to that typically used when capturing images.
Step 7. Click on the Camera… button to bring up the Camera
Setup window. Then click the Get White Reference button. Click
Yes in the Global White Reference window. The software now
scans the white image area to identify unevenness in light intensity
across it's surface.
Step 8. Click Ok in the Camera Setup window to exit.
Setting Shadow and Highlight Color Balance Values
It's
helpful to reestablish the shadow and highlight color balance values
from time to time as the lighting intensity changes when light bulbs
age or are replaced, or if the lighting setup is modified. (For additional
information about setting color balance values see the ProgRes plugin
user's manual [Release 3.x, June 1996], pp. 3-11 to 3-13 and pp. 3-21
to 3-23, and the plugin online Help files.)
Step
1. Turn on the camera using the green switch on the power supply.
Step 2. Open Photoshop. Select File>Import>ProgRes_v.4.01.
Step 3. Remove the camera lens cap and position the GretagMacBeth
ColorChecker chart under camera in the center of the area where herbarium
sheets are placed for image capture.
Step 4. Click on the Configure... button in the ProgRes Plugin
window. Make sure the selected Colour Matrix file is the one used
for capturing images with the current lighting setup (normally ps_reflect1.mtx).
Also make sure that Shading Correction: White and Black is marked
with a check. (These settings may be reestablished by clicking the
Load... button in the Configuration window, and opening the
config1.con file.) Click Ok to exit the Configuration window.
Now restore the color balance values to their default settings by
clicking the Reset button in the ProgRes Plugin main window.
Make sure the Overexposure box is checked, and that the Exposure time,
as indicated in the lower left portion of the plugin window, is set
to 1.
Step 5. Establish the normal lighting conditions used to capture images.
(See Lighting Setup in Capturing and Processing Digital
Images of Plant Specimens in the University of North Carolina Herbarium
for more information on this topic.) Remember to turn off the room
overhead lights. Adjust the camera's aperture ring so that the image
is as bright as possible in the plugin display window, but without
any overexposed areas as indicated by the "false" green
color.
Step 6. Click on the Start Focus button, and adjust the lens
focal ring until the image is sharply focused. (It's often helpful
to use the black and white focusing device for this process. See Capturing
Images with the ProgRes Camera in Capturing and Processing Digital
Images of Plant Specimens in the University of North Carolina
for details on focusing.)
Step 7. Click the Prescan button. Once the ColorChecker chart
has been scanned set the image size to 100% so that the entire chart
is visible in the display window.
Step 8. Click the Set White button. Using the mouse move the
dropper icon over the white square in the image of the color chart
and observe the RGB values displayed on the left side of the plugin
window. Clicking on a point with the left mouse button selects it,
defining it as white for the ProgRes software. Ideal points to select
for defining the white value, in order to produce high quality images,
have RGB values that are all equal or close to 240. You can visually
double check the results of your selection by clicking on the Undo/Redo
button to make "before and after" comparisons. (The Auto
White button chooses the brightest pixel in the image to define
the white value. This produces poor results if any pixel in the image
is overexposed. Clicking the Reset button restores color balance
values to their default settings.)
Step 9. Now click the Set Black button. Move the dropper icon
over the black square in the color chart, or the black band on the
far right of the image, and observe the RGB values displayed on the
left side of the plugin window. Clicking on a point selects it and
defines it as black for the ProgRes software. Ideal points to select
for defining the black value have RGB values equal or close to 20.
(The Auto Black button chooses the darkest pixel in the image
to define the black value.)
Step 10. If the results of choosing points to define white and black
values appear satisfactory, click on the Balance... button
in the ProgRes Plugin main window and click Save.. in the Colour
Balance window. Give the file a new name with the .tac extension,
or choose the bal1.tac file to overwrite the existing color balance
file. (The bal0.tac file contains the default color balance settings
and has been set as "read-only" so that it can't be easily
overwritten.) Click Save, and then Ok to exit the Colour
Balance window. Click the Online button in the ProgRes Plugin
window to exit Prescan mode and return to live image display in order
to capture images.