This section of the EgyGene GelAnalyzer4 software: Image Analysis part includes the necessary commands to adjust the image size.
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The gel image is displayed on the screen with two methods: Fitting the imge or viewing it with its actual size. Fitting the image method adjust the image size in respect to the screen size. While the second method displays the real size of the image. You can zooming the image to see its bands clearly which enables the correct band detection.
Tutorial video
(Set the video quality to 720 to be clear)