A set of manual controls for controlling the alignment of adjacent images is provided on the right side of the AutoStitch dialog:
These controls provide means of handling rotation of the camera about the line of sight (camera roll), as well as rotation of the camera about a horizontal axis perpendicular to the line of sight (up/down tilt). Additional controls for handling the rotation of the camera about the (vertical) axis of the panorama are provided in the Image Edit window.
A step-by-step procedure for using the manual stitching controls to align the images in a scene is presented below.
The camera tilt and roll controls work by changing the current camera orientation settings by an orientation "step". The size of the orientation step is determined by the Adjustment Step Size slide bar. The current Adjustment Step Size is shown in a box on the right side of the slide bar. A step size of "1" corresponds to roughly a one pixel change in the image rotation settings.
If the "Align All Sides" option is in effect, the camera tilt and roll adjustments are applied to all images in the current set of images. This method can be used to compensate for systematic errors in the camera orientation, where all images share a common defect. Such systematic errors can occur, for example, when using a tripod which has not been levelled adequately.
In addition, when the "Align All Sides" option is in effect, a button labelled Minimize Adjustments is located below the Camera Angle Adjustments box. The purpose of this button is described below.
If the "Align Selected Seam" option is in effect, the specified camera roll adjustments are made to the pair of images sharing the selected seam, and the camera tilt adjustment is applied only to the image identified as the "Right Image". This method can be used to compensate for random orientation errors such as those found when using a hand-held camera.
Return to Manual Stitching Controls (top).If the original flat images have been captured using a hand-held camera, or suffer from any of the defects identified under Stitching Problems the following procedure may be used to stitch the original flat images into a complete panoramic image:
If no problems have been encountered in any of these steps one may click on the "Stitch" button to close the Autostitch dialog, then continue with Exposure Balancing. Otherwise, it may be necesary to return to the Image Edit window for each image on either side of a problem seam, drag the vertical clipping lines to a common feature, and use the "Roll+" and "Roll-" buttons to restore the alignment at these seams. Take care to select "Align Selected Seam" before using the "Roll+" and "Roll-" buttons.
Set the Search Range slider to "Tweak" or ""Disable" for any problematical seams, and set the Search Range slider to "Narrow" or "Tweak" for any other seams. Then click on the "Start" button for each seam to improve the quality of each seam. After reaching the best possible alignment for each seam, click on the "Stitch" button to close the Autostitch dialog, then continue with Exposure Balancing.
Return to Manual Stitching Controls (top).The camera roll adjustments are controlled by two buttons labelled "Roll-" and "Roll+". The effects of these buttons are complementary to each other, and the effect of one can be undone by the other.
If the "Align All Sides" option is in effect, the "Roll+" button shifts the columns of each image so that the left edge moves down while the right edge moves up. This type of correction can be used to adjust a set of images captured using a camera mounted on a tripod, where the tripod head is not level (or not perpendicular to the tripod axis of rotation).
If the "Align Selected Seam" option is in effect, the "Roll+" button shifts the columns in the "Left Image" so that the right edge moves up while the left edge remains unchanged, and the columns of the "Right Image" are shifted so that the left edge moves down while the right edge remains unchanged. This preserves the alignment of each of these images with the other images representing this scene. This type of correction is most useful for working with images captured from a hand-held camera.
Return to Manual Stitching Controls (top).The camera tilt adjustments are controlled by a pair of buttons in the center of the Camera Angle Adjustments box. These buttons appear above and below the "Up/Down" label. As with the camera roll buttons, the effects of these buttons are complementary to each other, and the effect of one can be undone by the other.
The camera tilt angle adjustments make it possible to compensate for errors in the original images resulting from failure to aim the camera in a direction perpendicular to the axis of rotation. Such errors can arise from several sources:
For example, the photographer is standing on a tall tower or mountain top, and all of the interesting scenery is below the level of the photogapher, so the photographer points the camera down at the "interesting stuff". Alternatively, the photographer is surrounded by tall buildings, so the camera is pointed up at the second story level instead of straight ahead at eye level.
The camera tilt adjustment function corrects each original image for errors in the camera tilt angle by using the original image to calculate the image that would have been captured if the camera had been aimed "straight ahead" instead of "up" or "down".
The effect of the camera tilt angle correction can be seen in the Image Edit window. A small "+" in or near the center of the image shows the point at which the camera has been aimed (where the view direction intersects the scene). A horizontal line shows where the "horizon" intersects the scene. The "horizon" is defined by a plane at eye (camera) level perpendicular to the vertical axis of the panorama. Initially, the "+" falls exactly on the horizon line (so the horizontal portion of the "+" disappears).
If the "+" mark in the center of an original image is found at a point located above the level of the camera, it shows that the camera was pointed "up" instead of "straight ahead". In this case, the camera tilt buttons must be used to adjust the level of the horizon line until the horizon line passes through the original image at "eye level".
At this time, there is no automated means of determining the camera tilt angle. The only means of determining the camera tilt angles is to use the "Up/Down" buttons to ensure that the horizon lines pass through each original image at the "eye level".
If the "Align All Sides" option is in effect, the tilt angle values for all of the original images are incremented by the amount indicated by the "Adjustment Step Size" slider. In this case, a step size of "1" unit corresponds to moving the horizon line by one pixel.
Return to Manual Stitching Controls (top).The manual stitching controls and the automated stitching controls all operate on a seam-by-seam basis. Each operation attempts to optimize the alignment of a single pair of adjacent images. The result is a set of camera tilt and roll angles for each image comprising the scene. Although these results provide valid solutions for each seam, they are not necessarily the best solution for the entire panoramic scene.
The "Minimize Adjustments" function examines the current set of camera tilt and roll angles and replaces these with a new set of angles optimized for the entire scene while preserving the alignment of each individual seam. This operatiuon is based on the following assumptions:
On the basis of the first assumption, the average camera tilt angle for the entire scene is determined based on the set of camera tilt angles previously determined based on each individual seam. The resulting average tilt angle is then subtracted from the camera tilt angle associated with each image. This ensures that the average camera tilt angle for the entire scene is zero.
If the average camera tilt angle is not zero, as the result of systematically pointing the camera up or down, then either this function should not be used, or the average camera tilt angle must be entered or restored after using this function. A non-zero average camera tilt angle can be imposed by selecting "Align All Sides", setting an appropriate value for the "Adjustment Step Size", then clicking on the Tilt-Up or Tilt-Down buttons.
On the basis of the second assumption, the average camera roll angle for the entire scene is determined based on the set of camera roll angles previously determined based on each individual seam. The camera roll angle associated with each image is then replaced with the resulting average roll angle, and the corresponding image tilt angles are adjusted to preserve the alignment at each seam.
Repeating this fuction has no further effect.
The "Minimize Adjustments" operation attempts to preserve the alignment of all seams. Depending on the size of the adjustments applied by this operation, however, it may be necessary to repeat the stitching calculations with a "Narrow" or "Tweak" setting for the Search Range.
This button is available only when the "Align All Sides" option is in effect.
Return to Manual Stitching Controls (top).