Capturing Panoramic & Composite Images
Panoramic Photography
Panoramic photography is a term used to describe photographs that have a very
large field of view. In most cases, the field of view is 360 degrees in the
horizontal by 180 degrees in the vertical, capturing photographic information in all
directions. These images are viewed using a program like QuickTimeVR where
users can navigate the panorama by scrolling in any direction up, down, left, or
right in all directions. Panoramic images prove to be very useful for site
documentation, since they can be used for multiple purposes; QuickTimeVR
tours, texturing point cloud data, and for computer rendering different lighting
conditions.
I. Capturing Panoramic Images
The most effective way to capture panoramic images is to take multiple
overlapping photos and use a computer program to register them together into
one panoramic image. Although any camera and lens combination can be used
to capture a panoramic photograph, there are ways to optimize the process for
achieving the desired resolution and quality with minimal effort.
II. Spherical Panorama Head Purchasing or making a spherical panorama head
for your camera will greatly increase the accuracy and speed with which a
panorama can me taken. A spherical panorama head allows for the camera be
rotated in all directions around the nodal point of the lens. When taking multiple
pictures, rotating around the nodal point eliminates parallax between pictures for
precise alignment of images. Make sure when choosing/making a panorama
head is to make sure that it can support the weight of your camera and lens.
Some other highly recommended features are degree markings, click-stops, and
movable axis.
III. Finding the Nodal Point To find the nodal point, the most effective way is to
attach your camera to the spherical panorama head, rotate the camera while
looking through the view finder, and check for parallax. To make it easier to
notice parallax, mount a paper tube to a wall and set the camera up to look
directly down the tube. Next, rotate the camera and see if the back opening of
the tube moves relative to the front opening. If so, re-adjust the axis on the
spherical panorama head until there is no relative movement. Mark on the
spherical panorama head, or write down the axis positions for that camera and
lens combination.
IV. Lock Aperture When taking pictures for a panorama, it is important that the
camera have a constant aperture. This is because the aperture size determines
the depth of field for the photograph. A small aperture opening (large f-number)
has a very large depth of field, meaning that both close and far objects in a scene
should be in focus. The aperture needs to be as small as possible that still allows
for reasonable fast shutter speeds. Try dialing the aperture f-stop up until the
shutter speed to no less than 1/60th of a second outdoors and 1/20th of a second
indoors.
V. Lock ISO ISO is the International Standards Organization designation for
sensitivity of the camera sensor to light. An ISO of 200 will expose twice as fast
as an ISO of 100. The higher the ISO of the sensor, the more noise artifacts will
show in the image. When taking high quality photographs try to keep the ISO as
low as possible. For panoramic images try not to exceed an ISO of 400 and
make sure that the ISO of the sensor is locked for the duration of the panorama.
VI. Lock White Balance White balance sets the temperature in Kelvin’s of the
light source for a given photograph. If the white balance is set correctly, a
photograph of a white surface will appear white in the photograph. If the whitebalance is set too high or too low, the white surface will appear blue or red. For
most applications, white balance is set to the sun (5000K) but it may actually be
much less, say for indoor lighting with standard light bulbs (2800K). Most
camera’s come with a variety of pre-determined white-balance settings for
daylight, overcast days, fluorescent, incandescent, etc. so use the one that most
accurately describes the light source for a given scene. If you are unsure of the
white-balance, you can take a measurement from a photo of a white piece of
paper or digital grey card. Check your cameras manual for setting the white
balance. Make sure that for panoramic photographs you lock the white balance
before shooting the photos.
VII. Lock Exposure Locking exposure on a camera sets the ratio of aperture,
shutter speed, and ISO so that a consistently exposed image is created across
multiple exposures. For shooting a panorama, make sure that the metering mode
on the camera is set to matrix, therefore averaging the light-meter reading across
the entire frame. Also, the ISO and aperture should be locked before setting the
exposure lock so that only the shutter speed is locked when exposure is locked.
When locking exposure be sure to use a light meter reading that is representative
of the entire scene being photographed.
VIII. Average Meter Reading Find an area of the scene that has an average
amount of light and lock the exposure to that region. For example, if the scene
being photographed for a panorama is half in the sunlight and half in the shade,
align the viewfinder of the camera until half of the composition is in the light and
half in the shade then lock the exposure. Take a test photograph of a light and
dark area and see the results. The area in direct sunlight will be a little
overexposed and the area in the shade will be a little under exposed. As a
general rule it is better to err on the side of underexposure since it is easier to
adjust and underexposed image than an over exposed one. If it is necessary that
every portion of the panorama be exposed properly, then you will need to bracket
exposures appropriately.
IX. Bracket Exposures Exposure Bracketing is a setting on the camera that will
take photographs above and below the metered exposure by varying shutter
speed. When shooting a panoramic photograph it helps to bracket exposures
until you achieve a result where both the light and dark areas are properly
exposed. This is will increase the dynamic range of the scene, allowing for the
processed panoramic image to be lightened and darkened after shooting. If the
bracketed images capture the very lightest and darkest regions of the scene, the
dynamic range will be wide enough to be considered a high dynamic range
image.
X. Capture Panorama Capturing a multiple exposure panorama means that
there will be many individual images taken for a scene that will be processed into
a single panoramic image. Because there are many individual photos, it will take
some time to photograph a panorama be sure to have a consistent routine for
each panorama so that no photographs are accidentally skipped or duplicated.
Also, be aware of moving subjects of a scene (i.e. people, clouds, trees,
automobiles, etc) since they may appear unnatural in the resulting panorama (i.e.
same person showing up multiple times, car cut in half, etc.).
XI. Top-Down/Bottom-Up Methods Before taking photos look to see what
portions of the scene are moving and try to take the photographs in an order that
reduces the time differential between overlapping photographs. There are two
general methods for the capture order of a multi-row panorama; shooting from
the top-down, or from the bottom up. Shooting a top-down panorama is usually
the most effective way to capture a multi-row panorama since it allows for taking
the last photo straight down without the tri-pod. Some example situations of when
to use a top-down method are when photographing sun-rises, sunny days,
overcast days, partially cloudy days, indoor environments, and any time you want
to shoot a photograph straight down to eliminate the tripod from the panorama.
Shooting bottom up is usually not recommended except for sunsets.
XII. Finishing Touches There are some suggestions for turning a good
panorama into a great panorama, and they involve keeping in mind a couple of
problem areas in a panorama, such as lens flare and the tripod.
XIII. Lens Flare Removal Direct sunlight hitting the lens is the most common
cause of lens flare, resulting in one or more photographs to be overexposed. Try
to set up the camera so that the sun is not directly hitting the lens (shady areas).
If this is not an option, then use a technique where several images are
photographed of the sun; one with the lens flare, one covering just the sun with
an opaque object from one side of the frame, and one covering the sun with the
same opaque object from the other side of the frame. Later, these three
photographs can be altered so that the arm and opaque object are removed, and
the sun inserted.
XIV. Tripod Removal The tripod will appear in every spherical panorama, and
there is a simple solution to removing the tripod from the panorama. First, make
sure to photograph in a top-down method, so that the last photo taken will be
straight down. After taking the photos straight down with the tripod in the
photograph, remove the camera and hold it in the same position as if it were still
being held in the spherical panorama head. Be sure that your feet are as far from
the tripod as you can manage while maintaining your balance, and that your
shadow is not cast over the area where the tripod was standing. Next, have
someone else move the tripod and take a couple images straight down. These
images will be used to remove the tripod from the final panorama.
Composite Photography
Composite images are captured by taking multiple photos and combining them
into a single image. These images are very useful when there needs to be very
high resolution texture data evenly across a surface, such as the front of a
building or a long flat surface. There are two methods for capturing composite
photos; nodal composites and mosaic composites.
I. Nodal Composite Images Nodal composite photography is a method for
capturing very high resolution image data of a 3D surface by taking multiple
photographs around the nodal point of the lens. By rotating the camera around
the nodal point of the lens, this eliminates parallax and allows for images to be
registered together seamlessly. This is effective for photographing 3D surfaces in
high detail, such as a detailed sculpture or an entire site from an adjacent hill.
Nodal composite photography is essentially the same method for capturing
panoramic images, except the field of view is usually along the lines of what a
single photograph would be. For example, it may take a 35mm lens to
photograph the corner of a building being documented. If a very high resolution
image is desired, a 110 mm lens might be used to photograph the same area by
taking 10 pictures in a nodal composite.
II. Mosaic Composite Images Mosaic composite photography is a method for
capturing very high resolution image data of a 2D surface by taking multiple
photographs and combining them into a single image. When capturing a mosaic
photograph it is important to lock the cameras exposure, maintain a
perpendicular view, have 30% overlap between images, and keep a constant
distance to the flat surface being photographed. These images are effective for
capturing large frescos, paintings, tapestries, etc. that are flat since three
dimensional surfaces have inherent parallax problems.