The Image Edit window provides a means to examine each of the original images comprising the current panoramic scene, a means to identify certain properties of each image, and an interactive means for controlling some of the properties of each image. The Image Edit window may be opened by double clicking on any part of the panoramic image in the main window.
The following figure shows an example of an Image Edit window:
This window shows one of the original flat images at a 1:1 scale (one image pixel per screen pixel). The name of the selected image and its sequence number (starting from zero) are shown in the title bar.
This window may be resized and scrolled, but the image scale is fixed. The Tab and Shift-Tab keys can also be used to hop to the adjacent images to the right and left. Any side image may be selected by double clicking on part of the panoramic scene derived from that side image.
The following features are superimposed on the image in the Image Edit window:
Most of these features can be controlled interactively, as described below. In addition, the image which appears in this window can be subjected to copy-and-paste operations. The copy and paste operations are based on the underlying image shown in this window, and they do not affect the features superimposed on this image.
To close the Image Edit window, click on the "X" on the right end of the title bar.
Return to Image Edit Window (top).A small "+" marks the point which has been identified as the optical center of the original image. The horizontal portion of the "+" will not be visible when this mark is superimposed on the horizon line.
Initially, the "+" mark is located at the point determined by one half the number of rows and one half the number of columns in the selected image. There should be no need to modify the location of the "+" mark as long as the selected image represents the complete untrimmed original image captured by the camera, or if the selected image represents a symmetrically trimmed portion of the original image captured by the camera.
If the selected image represents an asymmetrically trimmed portion of the original image captured by the camera, then the "+" mark should be shifted horizontally by one half the difference btween the number of columns trimmed from the left and right sides, and vertically by one half the difference between the number of rows trimmed from the top and bottom.
The "+" mark can be shifted by dragging it with the left mouse button. The cursor changes to a four-way arrow when the "+" mark is selected.
Asymmetrical trimming causes the optical center of an image to differ from the geometric center of the image. The optical center of an image corresponds to the point in the image where a line perpendicular to the image plane passes through the center of the lens.
Asymmetrical trimming seldom occurs with images obtained directly from a digital camera, but this can be a problem with scanned images obtained from film cameras. Most commercial film processing laboratories never provide "full negative" prints. Instead, the prints they deliver are always cropped, and the cropping is generally not symmetrical. Consequently, the geometric center of the scanned print is usually not exactly the same as the optical center of the original image.
Similar problems can be encountered if the film plane of a camera is not exactly perpendicular to a line passing through the center of the lens and the geometric center of the image capture surface (film, CCD, etc.). This type of error is usually negligible, except for specialized cameras specifically designed to allow the image plane to be tilted.
Return to Image Edit Window (top).The horizon line represents the intersection of the horizon plane with the scene. The horizon plane is defined by a plane perpendicular to the vertical axis of the panorama (the camera rotation axis) passing through the eye point (the lens of the camera). This feature is represented by a straight horizontal or diagonal line extending from the left edge of the Image Edit window to the right edge.
The slope and vertical position of the horizon line are controlled by the camera tilt and roll angles. Initially (zero tilt and zero roll), the horizon line appears as a horizontal line passing through the center point ("+"). A non-zero value of the camera roll angle will cause the horizon line to become diagonal with a slope determined by the camera roll angle. A non-zero value for the camera tilt angle causes the horizon line to pass above or below the center point ("+").
The horizon line typically passes near the center point ("+") with a small (nearly horizontal) slope. If the camera was pointed up or down by a large angle, the horizon line may appear closer to the top or bottom of the Edit Image window.
The horizon line should pass through the elements of the selected image which have the same elevation as the lens of the camera. In the case of an outdoor scene with an clearly visible distant horizon, the horizon line should be parallel to and very close to the visible horizon. Any separation between the horizon line and a visible horizon implies a need to adjust the camera tilt angle so as to reduce this separation.
Return to Image Edit Window (top).The Image Edit window contains a set of four clipping lines representing the left, right, top, and bottom boundaries of a clipped image derived from the selected image. When the image blending option is turned off, the complete panoramic scene is determined by warping each of the clipped images and concatenating the resulting warped clipped images. In this case, the left and right clipping lines indicate where the selected image abuts the adjacent images on either side. The top and bottom clipping boundaries serve no function except to exclude unwanted areas at the top and bottom portions of the selected images.
Even when the image blending option is in effect, the left and right clipping boundaries continue to represent reference points where adjacent images coincide. In this case, the right clipping boundary in one image and the left clipping boundary in the adjacent image both correspond to the same azimuth angle in the resulting panoramic scene.
Ideally, the positions of the left and right clipping boundaries are determined automatically by the automated stitching controls. If the automated stitching controls should fail to produce a satisfactory result, then one may use the left and right clipping boundaries to align the adjacent images manually.
The horizontal clipping boundaries of any image can be adjusted manually by placing the cursor on the right or left "vertical" line in the Image Edit window. When the cursor changes to a thin white double arrow, the selected clipping boundary may be dragged to a new position. When the left mouse button is released, the panoramic scene will be regenerated.
To align a pair of adjacent images, first compare the two original images and identify a conspicuous feature in the overlapping region shared by both images. Open the left image in the Image Edit window and drag the right clipping boundary to a prominent point on the conspicuous feature. This point should preferably be located near the center of the overlapping region shared by both images. Then, press the [TAB] key to select the next image to the right, and drag the left clipping boundary in that image to the corresponding point on the same feature.
After using the left and right clipping boundaries to establish the horizontal alignment of a pair of adjacent images, one may use the camera roll adjustments to establish the vertical alignment of the images.
Return to Image Edit Window (top).The blending boundaries (also called cropping boundaries) are represented by black areas along the left, right, top, and bottom areas of the image in the Image Edit window. The following figure shows an example of these black areas:
These black areas cover portions of the original images that are excluded from the image blending process. When the mouse is located on the left or right blending boundary, the cursor changes to a fat white double arrow. The blending boundaries have no effect unless the image blending option is active.
Setting the blending boundaries is equivalent to using an external image processing utility to trim the original images down to the size represented by the blending boundaries The advantage of the blending boundaries is that they allow the extent of the trimming or cropping to be determined interactively and reversibly with immediate feedback based on exactly how the amount of trimming affects the resulting panoramic image as seen in the main window.
Initially, the blending boundaries coincide with the boundaries of the original images, so no black areas are visible around and of the images. When the blending function is activited for the first time for a given scene, the blending boundaries are moved to positions midway between the original image boundaries and the current clipping lines.
The blending boundaries can be adjusted manually by placing the cursor on the edge of the black area and dragging the boundary with the mouse (with the fat white double arrow). Moving the blending boundaries out toward the original image boundaries provides a softer blend, but also increases the risk of ghosts and "double vision" artifacts. Moving the blending boundaries towards the center of an image provides a sharper transition from one image to the next, but this can be used to eliminate "ghosts" caused by people or other objects which may have moved between the capture of one image and the capture of the next image.
The blending boundaries can be moved inside the clipping lines, but if a blending boundary of one image is shifted to a point beyond the corresponding blending boundary in the adjacent image, the resulting cropped images will no longer overlap and a black band will appear in the resulting panoramic image.
Placing the cursor on the clipping lines changes the cursor to a thin white double arrow. The thin white double arrow can be used to drag the clipping lines, thereby altering the image alignment. Be careful not to drag the clipping lines if the adjacent images are already properly aligned.
Return to Image Edit Window (top).