| 摘要 |
Methodologies and systems to compare images with different levels of contrast are provided. Contrast is normalized between the images with different contrast levels and brightness is set. When normalizing contrast a derivative of gray level is determined for a first digital image having a first contrast level, and a derivative of gray level is determined for a second digital image having a second contrast level that is greater than the first contrast level. A ratio of the derivative of gray level for the first digital image to the derivative of gray level for the second digital image is determined, and the derivative of gray level for the first digital image is equalized with the derivative of gray level for the second digital image. Brightness of at least one image may be set automatically, such as by calculating an average pixel value excluding background and text, or manually.
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