Click on the "Exposure" button to open the Balance Exposures dialog. As shown in the following example, this dialog displays the name of the currently selected image, the gamma value for this image, and the exposure change value for this image.
There are several buttons below the Exposure Change value. The most important of these buttons is the one labelled "Balance All". In the case of a well-behaved set of images, this is the only button that will be needed, although it may be necessary to select this button several times to achieve a satisfactory balancing of exposures. The other buttons allow one to override the calculated exposure correction values in case of problems.
After completing the exposure balancing operation, click on the "Exposure" button to close the Balance Exposures dialog. Then procede to the image blending operation.
Return to Balancing exposures (top)To see the gamma value and exposure change value for any image, simply browse through the scene in the main window until the portion of the scene resulting from this image can be seen in the center of the main window. Positive values for either value represent increased exposures (brighter images) compared to the original images, and negative values represent decreased exposures.
The "Exposure Change" value represents a linear exposure correction factor for all pixels in an image. This is calculated by comparing the left side of each image to the overlapping portion of the adjacent image to the left, except that the first image is not compared to the last image. Positive values of the "Exposure Change" value tend to bleach out bright portions of an image, and negative values can turn bright areas into a muddy gray. Consequently, large values of the "Exposure Change" value can cause very unsatisfactory changes to the colors in each image.
The "Gamma Value" represents a non-linear exposure correction that preserves high and low levels of each color while increasing or decreasing intermediate intensity values. This results in much better exposure adjustments than are obtained from the linear "Exposure Change" factor, but the calculation of the "Gamma Value" is more difficult than the calculation of the "Exposure Change" factor. Each time the "Balance" or "Balance All" operations are performed, a new "Gamma Value" is determined based on previous value for the "Exposure Change" factor. This causes the "Exposure Change" values to be reduced to smaller values while transferring all of the exposure balancing effects to the "Gamma Value". If all of the "Exposure Change" values are within the range of +1% to -1%, then there will be little or no bleaching or muddying of light areas of any image.
Return to Balancing exposures (top)The "Balance" button is similar to the "Balance All" button, except that the "Balance" button performs the exposure balancing calculations only to the currently selected image as identified in the "Image Name" field. This may be used in problematical situations where some exposure values must be set "manually" and others can still be determined automatically.
Return to Balancing exposures (top)The "Reset All" button sets all exposure and gamma values back to zero (the initial default). This can be used to "start over" if anything goes awry with the exposure balancing calculations. Don't use this button except in an emergency.
See the following section for a list of conditions that may cause the exposure balancing calculations to fail.
Return to Balancing exposures (top)For a well-behaved set of original images, there should be no problems with the exposure balancing operation. Problems can arise in any of the following conditions:
In such cases, one may enter the exposure values manually, using a trial-and-error approach until satisfactory results are reached. Values entered manually take effect when the "Apply" button is selected. Exposure values may be calculated automatically for individual sides by selecting the side, then selecting the "Balance" button.
No matter how they are determined, the exposure values cannot replace missing data. If there are gaps or sever exposure variations, it may be best to recapture the entire scene with better lighting conditions.
Return to Balancing exposures (top)The automatic exposure adjustments are performed relative to the first image in the current set. If the exposure values for the first image are increased (manually), then subsequent application of the "Balance All" function will increase the exposure values for all other images. Entering negative values for the exposure values for the first image will cause all subsequent images to become darker then the "Balance All" operation is performed.
Manual changes to the current exposure values can be entered directly in the "Gamma Value" and "Exposure Change" data boxes. Such values take effect when the "Apply" button is selected. Manually entered values may be disregarded when the "Balance" or "Balance All" operations are performed.
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