Compare

This transformation lets you compare two images using a variety of methods. One of the images is the input image (Image A) and the other you select (Image B). A preview area occupies the bottom part of the dialog box and displays the differences between images A and B according to the selected method. The size of the preview area can be adjusted by resizing the dialog box.

Image B

This image picker control lets you select image B. Image A is always assigned to the input image, i.e. the preceding image in the image browser. By default, when the transformation starts up, Image B is assigned to the image preceding the input image, if any. If no image is selected, image A is used for both images.

If the two images have different widths or heights in pixels, the smaller of the two images is padded with a white border to match the larger one.

Image A, Image B

The captions of the two images are displayed here. A label is also displayed just above the preview area indicating the current orientation of the two images.

Method

This tool bar lets you select how you want to compare images A and B.

 Curtain -- Displays the two images superimposed with a divider you can move from side to side like a curtain. The divider location is displayed as a vertical line that runs from the top to the bottom of the image. Drag the divider left or right to see more of one image and less of the other. By default, image A is on the left, but if you shift-click anywhere in the preview area, the positions of the two images are swapped.

 Horizontal -- Displays the two images side by side. By default, image A is on the left, but if you click anywhere in the preview area, the positions of the two images are swapped.

 Vertical -- Displays the two images one above the other. By default, image A is on top, but if you click anywhere in the preview area, the positions of the two images are swapped.

 Difference -- Displays image A minus image B, offset so the result is mid-level gray where they are equal. The Strength slider (see below) appears when this method is selected so you can exaggerate differences to make them more visible. Clicking anywhere in the preview area toggles the display between A–B and B–A.

 Difference -- Displays image B minus image A, offset so the result is mid-level gray where they are equal. The Strength slider (see below) appears when this method is selected so you can exaggerate differences to make them more visible. Clicking anywhere in the preview area toggles the display between B–A and A–B.

 A -- Displays just image A. Clicking anywhere in the preview area toggles the display between A and B.

 B -- Displays just image B. Clicking anywhere in the preview area toggles the display between B and A.

 Blink -- Alternately displays images A and B at a blink rate you specify with the Blinks/sec slider (see below).

Zoom controls

This tool bar lets you zoom in to compare images in greater detail.

 Zoom In -- Increases the magnification factor to show more detail. Four steps equals a 2X increase.

 Zoom Out -- Decreases the magnification factor to show more of the images. Four steps equals a 2X decrease

 Zoom to Fit -- Sets the magnification factor so the image just fit in the preview area.

 Zoom to1:1 -- Sets the magnification factor so one pixel of the display equals one pixel in the images.

Zooming and scrolling only affect the preview area – when you click OK or Apply, the output image includes all of both images. If the Blink method was selected, the output image is a copy of image A.

Scroll Bars

Whenever the images are zoomed larger than the available space in the preview area, scroll bars are displayed to let you see different parts of the images.

Blinks/sec

This slider only affects the Blink method – it controls the blink rate in frames/second.

Strength

This slider is only displayed when the difference method is selected. It magnifies differences between the two images, making small variations easier to see.