Fraunhofer STAN User manual

STAN - The Stereoscopic Analyzer
Manual: version 2.10-0-1-Z

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STAN Manual STAN version 2.10-0-1-Z
Overview
Introduction................................................................................................................................ 2
First Steps ................................................................................................................................... 3
Select Input Device ................................................................................................................. 3
Select Input Raster.................................................................................................................. 4
Adjust Vertical and Horizontal Flip ......................................................................................... 5
Calibrating your Stereo Rig......................................................................................................... 8
Mechanical Alignment............................................................................................................ 8
Roll Error Adjustment ........................................................................................................... 12
Vertical Offset Adjustment ................................................................................................... 12
Keystone Error Adjustment .................................................................................................. 12
Tilt Keystone Error Adjustment ............................................................................................ 13
Y-Offset Adjustment ............................................................................................................. 13
Zoom-Level Adjustment ....................................................................................................... 13
Calibration Options............................................................................................................... 14
Depth Volume adjustment....................................................................................................... 16
Measuring the Depth volume............................................................................................... 16
Adjusting the Interaxial Distance / Stereo Baseline ............................................................. 17
Adjusting the Convergence / Angulation ............................................................................. 19
Horizontal Image Translation (HIT) / Sensor Shift................................................................ 22
Visualization of the Depth Structure .................................................................................... 22
Color Adjustment Assistance ................................................................................................... 24
Color Temperature assistance.............................................................................................. 24
Brightness Assistance ........................................................................................................... 25
Electronic Image Alignment ..................................................................................................... 27
STAN –Specifications ........................................................................................................... 28
HD-SDI Input Formats ........................................................................................................... 28
Working Directory ................................................................................................................ 29

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Config File settings................................................................................................................ 29
Width and Height of the GUI: ............................................................................................... 30
Enable HDMI-Output ............................................................................................................ 30
Width and Height of the HDMI-Output Window: ................................................................ 30
HDMI-Output mode:............................................................................................................. 30
Width and Height of the HDMI-Output Window: ................................................................ 31
Side-by-Side HD-SDI Input: ................................................................................................... 31
Auto-Rescaling for HDMI-Output ......................................................................................... 31
Auto-HIT................................................................................................................................ 31
Motor Control....................................................................................................................... 31
Auto-Interaxial...................................................................................................................... 32
Auto-Convergence................................................................................................................ 32
Depth Plane Parallax Range.................................................................................................. 33
STAN Processing Speed ........................................................................................................ 33
Introduction
The STAN (Stereoscopic Analyzer) is an assistance system for stereo shootings and 3D
productions. An image-based scene analysis estimates in real-time the stereo geometry of
the two cameras in order to allow an optimal alignment of the cameras and lens settings
directly on the set. It automatically eliminates undesired vertical disparities between the two
views, through an electronic image rectification process. In addition it detects the position of
near and far objects in the scene, derives the optimal interaxial distance and gives alerts if
synchronization problems occur.
Figure 1 illustrates the Graphical User Interface of the Stereoscopic Analyzer. The GUI allows
an easy overview about all important stereoscopic parameters. The input images can be
monitored in a variety of visualization modes.

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Figure 1: STAN's Graphical User Interface (GUI)
First Steps
Select Input Device
If your PC system has more than one HD-SDI Input Device, choose the appropriate capture
board from the Drop Down. Figure 2 illustrates this process.
Supported capture boards are:
DVS Centaurus II
DVS Atomix
DVS Atomix LT
Blackmagic Design DeckLink HD Extreme 3D

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Figure 2: Input Device selection: Options  Video  Input Device.
The options menu is automatically opened after the start of the application when no
camera signal matching the current Input Raster could be detected. After changing the
Input Device, click Restart.
Select Input Raster
In a first step, the proper Input Raster needs to be chosen. The Input Raster is a combination
of the resolution, the frame rate, and the scan mode (progressive or interlaced). Select the
Options tab and use the drop-down menu to choose the Input Raster as shown in Figure 3.
Briefly, the Input Raster must match the configuration of the Monitor Output or the
Recording Output of your cameras.
The Input Raster can be selected in the Options tab. Within the Options tab, select the Video
tab.
SDI Input Device

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Figure 3: Input Raster selection: Options  Video  Input Raster
The options menu is automatically opened after the start of the application when no
camera signal matching the current Input Raster could be detected. After changing the
raster, click Restart.
After the first start the STAN shows the video settings in the Options tab. It is necessary to
select the proper Input Raster from the cameras. All supported Input Rasters can be found
in the ANNEX. Please note that some video equipment cannot distinguish between a psF-
Raster (progresseive scan mode using two fields as done in interlaced mode) and an
Interlaced-Raster. The psF-Raster is widely used by Sony cameras but is not specified in
SMPTE 292M.
Adjust Vertical and Horizontal Flip
When using a mirror rig, you will need to flip one or both cameras vertically or horizontally.
Before you can start working with the STAN. Figure 4 shows an example of a stereo pair
which needs a vertical flip to be applied on the left image. The left camera image was flipped
by using a mirror rig.

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Figure 4: Unmodified camera signals. The left image is flipped due to the use of a mirror rig
while shooting the content. Using the Side-by-Side view mode, one can easily perceive
which flipping option is necessary.
We know choose the appropriate flipping in the Options menu as shown in Figure 5 and
Figure 7. In our example we need to flip the left image vertically.
Figure 5: Select the appropriate flipping in the Options menu. In our example, the left
image needs to be flipped vertically. Changes apply immediately.
After applying the flip, we switch back to the Side-by-Side view mode to check the result of
the flipping settings as illustrated in Figure 6. Apparently, we do now have a valid stereo pair.
Figure 6: Stereoscopic image pair. The left image has been flipped vertically to compensate
for flipping introduced by the mirror rig. You can start using the STAN now.
Some stereo rig configurations might require to flip both cameras vertically and one camera
horizontally.

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Figure 7: Vertically or horizontally flip the images when using mirror rigs. You can define
the flipping in the menu:
Options  Video  Flip Left Image / Flip Right Image
As shown in Figure 7 you can also swap the left and right input channel. If for instance, the
left camera is connected to the right STAN input channel (and the right camera to the left
STAN input channel) you can use this feature to compensate this erroneous configuration.
Figure 8 illustrates this process.
Figure 8: Swap the left and right camera input on demand. The changes apply immediately
When you change the flipping settings and/or the swapping settings, these apply apply
immediately, i.e. no restart is required.

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Calibrating your Stereo Rig
Mechanical Alignment
One of the main features of the STAN is to provide assistance for the mechanical alignment
of the rig. In Figure 9 the results of the geometrical analysis are illustrated. In this example,
Roll, Vertical, Keystone, Tilt-Keystone, Y-Offset and Zoom settings are being evaluated and
displayed.
Figure 9: Displaying the parameters for the Mechanical Alignment.
To achieve an optimal mechanical alignment the red marked values in Figure 9 need to be
calibrated as:
Roll –0°
Vertical Offset –0%
Keystone –0%
Tilt Keystone –0%
Y-Offset –0%
Zoom Level –100%
In general, during the setup and calibration phase, you should try to get near the above
mentioned values. Depending on which stereo rig you use, it might happen that you need to
calibrate some values iteratively.
To perform the adjustment, use the appropriate calibration knobs and/or screws on your
stereo rigs, and turn them until all values are near the optimum.
In addition, you might want to get a visual feedback. To do so, choose one of the overlay
modes in the Overlay menu as shown in Figure 10 to Figure 12.

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Figure 10: The Anaglyph Overlay mode can be used to get a visual feedback of the quality
of the mechanical alignment. Red or cyan lines around horizontal object borders in the
image are clear indicators of the presence of vertical disparities and thus a poor
mechanical alignment.
The Anaglyph Overlay mode is widely used to assist the calibration of the stereo rig. Red
and Cyan border indicate differences between the left and the right image. This can be used
to identify vertical disparities indicating a missing calibration of the stereo rig. Moreover,
one can easily detect horizontal disparity and especially the convergence plane. This assists
the stereographer the choose the right convergence angle or Horizontal Image Translation
(HIT). One can choose between three Sub-Options:
Input
Program
Preview
These options define, if the uncorrected image pair sill be shown in the anaglyph overlay
(Input), or if electronically corrected images shall be shown (Program and Preview).
Program refers to the correction parameters which are active on the HDMI-output while
Preview applies correction matrices which become active when hitting the button Rectify.
These Sub-Options are also available for the visualization modes Difference and Opacity
Overlay.

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Figure 11: Difference Overlay Mode. The Difference Overlay Mode shows the luminance
difference between the two images.
The Difference Overlay Mode is also widely used to perform the mechanical calibration of
the rig and to choose a proper convergence plane. In the Difference Overlay mode, all
objects in the convergence plane disappear. These regions are displayed in grey. Vertical or
horizontal disparities yield to black and white edges around the objects.

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Figure 12: Opacity Overlay Mode
Figure 13: The Cut-Off Area mode combined with the Side-by-Side view mode allows for an
optical feedback of possible calibration errors. In this example, the right camera suffers

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from a 1.1° roll error. The white and orange rectangles ins the two images coincide with
the current camera geometry.
Roll Error Adjustment
The Roll error refers to a roll of the right camera with respect to the left camera. To reduce
the roll, error, you can turn the appropriate knob on your stereo rig (e.g. Quasar). A good
calibration yields to values within a range of +/- 0.1° Roll error.
Note: If you have a roll error of 1 °, and an image height of 1080 pixel, you would have
around 16 pixel of vertical offset at the left and right image borders. In comparison, a roll
error does induce vertical disparities near the image center.
Vertical Offset Adjustment
The Vertical offset is the mean disparity between the left and right image. It is measured in
percent of the image height. To reduce the Vertical offset, you can adjust the tilt of one or
both cameras.
Note: If you have a vertical disparity of 1 %, and an image height of 1080 pixel, you would
have around 10 pixel of vertical offset.
Keystone Error Adjustment
The Keystone error is induced by a convergent camera geometry. During rig calibration, one
aims to bring both cameras in a parallel geometry. The cameras are parallel when the
Keystone error vanishes.

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Note: When the Keystone error vanishes, the two cameras are in parallel position.
Tilt Keystone Error Adjustment
A Tilt Keystone error indicates the presence of a strong tilt error. Similar to a convergence
angle, a camera tilt also yields to a keystone. This effect can be observed for instance when a
projector is displays an image onto a wall and the optical axis is not perpendicular to that
wall. However, the Tilt Keystone error is usually very small and vanishes automatically when
adjusting the Vertical offset.
Y-Offset Adjustment
The Y-Offset indicates a height difference between the two cameras. The result is measured
in percent and refers to the ratio of height error and interaxial distance. If you have an
interaxial distance of 100mm and STAN indicates a Y-Error of 1%, your cameras are 1 mm off
in height.
STAN performs an image based measurement. For a robust measurement of the Y-Error,
please make sure that STAN can find objects in different planes. In doubt, you can check
using the Side-by-Side viewing mode with activated Feature Points display, if STAN finds
feature points in different depth planes. We also recommend to minimize all other errors
(e.g. Roll, Vertical, Keystone, Zoom, etc.) before minimizing the Y-Offset. This will yield to
more robust measurements.
Note: If you have an interaxial distance of 100mm and STAN indicates a Y-Error of 1%, your
cameras are 1 mm off in height. You cannot perform a Y-Error measurement with zero
interaxial distance. For a robust measurement, you need an object tracked by the feature
point detector near the camera, and also an object which is far away.
Zoom-Level Adjustment

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The Zoom-Level other than 100% indicates a mismatch between the two cameras’ focal
lengths, i.e. the two magnifications factors of the lenses are not identical. STAN measures
the ratio between the two focal lengths and displays it in percent. To minimize the error,
change the magnification factor of one of the two lenses, i.e. the zoom level, in case of fixed
focal length lenses, you might try another pair of lenses which might have better matching
focal lengths. Alternatively, you might move one camera along the optical axis. However, this
introduces a small perspective error, which can be neglected in most cases. Try to bring the
Zoom-Level in a region around 99.9 % and 100.1 %.
Note: When STAN measures 101.0% percent Zoom Level, the focal length of the right lens is
by 1% longer than the focal length of the left lens. This will induce vertical disparities of ca. 5
pixels near the top and the bottom of the stereo images when using full HD resolution.
Calibration Options
In the Fitting tab in the Options menu you can choose, which geometric parameters are
important four your calibration process. In many cases, Roll, Vertical, and Zoom are
sufficient to monitor, if the rig is still well calibrated, or if the mechanical calibration
procedure needs to be performed again. Figure 14 shows the corresponding dialogue in the
Options menu which is used to enable or disable the tracking of the different geometrical
parameters. All parameters which are tracked, will also be shown in the bottom area of the
GUI.

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Figure 14: Select the geometrical parameters to track: Options  Fitting  Roll / Vertical /
Keystone / Tilt Keystone / Zoom / Y Offset

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Depth Volume adjustment
Measuring the Depth volume
A key benefit of the STAN is the intuitive and precise measurement of the current Depth
Volume. The value is shown in the center of the colored Depth Bar in the lower left region of
the GUI. Moreover, the width of the Depth Bar is proportional to the depth volume. Figure
15 illustrates this relationship.
Figure 15: The Depth Bar: Measurement of the current Depth Volume. The Depth volume
in this example is 1.7 % of the screen width.
Beside the depth volume, STAN is measuring the amount of depth before the convergence
plane (i.e. Screen Plane) and behind the screen plane. These numbers are shown in Figure 15
above the captions Near and Far.
Another way to measure the Depth Volume is to use grid lines. You can overlay grid lines.
You can activate grid lines in the Overlay tab by pushing the Grid button. The position of the
grid can be moved left and right using the slider as shown in Figure 16. Use the sensor shift
(or HIT) to bring an object of interest (e.g. the nearest object) to convergence. Subsequently,
you can measure the disparity, for instance of the far clipping plane. A horizontal disparity of
2% corresponds to the spacing between two grid lines.

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Figure 16: Grid lines applied to an Anaglyph Overlay image. Each grid line corresponds to a
disparity of 2% of the image width. Use the slider to move the grid lines left and right. The
sensor shift (or HIT) can be used to bring the near clipping plane or the far clipping plane to
convergence.
The grid lines can be used to countercheck the automated depth volume measurement.
However, the fastest and more precise way to check the current Depth Volume, is to read it
right from the colored Depth Bar as shown in Figure 15.
Adjusting the Interaxial Distance / Stereo Baseline
Once the current Depth Volume has been calculated, you may want to adjust the interaxial
distance in order to meet your Depth Budget requirements.
The Depth Volume is constantly measured by STAN and displayed as shown in Figure 15. If
this number exceeds the Depth Budget, the STAN will give a feedback to increase or shorten
the interaxial distance. This illustrated in Figure 17.

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Figure 17: The Depth Volume (1.7 % in this example) is compared to the Depth Budget
(Total Parallax to be defined in the Options menu). Subsequently, STAN derives, in which
direction, the interaxial distance needs to be changed. In this example, the red arrow to
the right indicates that the interaxial distance needs to be increased drastically. If you
increase the Depth Budget (i.e. Total Parallax), STAN will take this into consideration and
suggest higher interaxial distances.
Note: You can hide or show the interaxial distance advices and/or the interaxial distance
gauge. To show the interaxial distance advices, go to Options  GUI and activate
Interocular: Show. If you want to display the convergence plane gauge in the GUI, activate
Interocular: Gauge in addition.
The interaxial distance gauge shows the current motor position if a connection to the rig
motors has been established. The colored arrows (left and right) indicate in which direction
the interaxial distance should be moved to in order to get an optimal result. They can turn
into red (very bad), yellow (bad) and green (good) or vanish (very good). The following table
summarizes the different indicates and resulting advices.
Symbol
Indication
Advice
The Depth Volume considerably
exceeds the Depth Budget.
Strongly reduce the interaxial distance
and/or increase the distance between

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stereo rig and the nearest object.
The Depth Volume exceeds the
Depth Budget.
Reduce the interaxial distance or
increase the distance between stereo rig
and nearest object
The Depth Volume slightly exceeds
the Depth Budget.
Slightly reduce the interaxial distance or
increase the distance between stereo rig
and nearest object
The Depth Volume perfectly
matches the Depth Budget
Optimal interaxial distance has been
found. Keep shooting.
The Depth Volume is slightly lower
than the Depth Budget
You might slightly increase the interaxial
distance in order to take full advantage
of your available Depth Budget or bring
the stereo rig nearer to the scene’s
nearest object.
The Depth Volume is lower than the
Depth Budget.
Increase the interaxial distance or reduce
distance between the stereo rig and the
nearest object in the scene.
The Depth Volume is much lower
than the Depth Budget. Objects
might look flat, or your scene
contains only a single depth plane.
Increase the Interaxial Distance or reduce
the distance between stereo rig and the
scene in order to bring depth into the
scene.
Table 1: Description of the indications and advices given by STAN in order to find the best
possible interaxial distance.
Note: The colors of the interaxial distance arrows depend on the 3D-Settings in the Options
menu. The Depth Volume is compared to the Depth Budget and a corresponding suggestion
is calculated.
Adjusting the Convergence / Angulation
Beside the interaxial distance, the convergence plane is the next important stereoscopic
parameter which needs to be set with care. STAN automatically calculates the position of the
Depth Bracket, i.e. the relative position of the Depth Volume to the convergence plane. The
amount of depth in front of the convergence plane and behind the convergence play are
displayed as shown in Figure 18.
Figure 18: Positions of the near- and far clipping planes are shown in the GUI. The values
are used to derive a suitable convergence plane.