Comparing Image Files

Merge image comparisons make it easy to compare various types of image file and see precisely which pixels have been modified.

Information If you haven’t already, spending a few moments browsing the Instant Overview of File Comparison and Merging will help you quickly become familiar with Merge file comparisons. It may also be helpful to review the Making the Most of the Ribbon topic.

Performing a comparison

To open a new image comparison:

  • Choose the New image comparison item in the drop-down menu of the leftmost ribbon item.
  • Or, if you are already viewing an image comparison, click the New image comparison button in the ribbon.
  • Or, press Ctrl+Shift+Alt+P.

The screenshot below shows a new, empty image comparison tab.

A new image comparison window

Two empty areas where the compared images will be displayed take up the majority of the window. Above each file pane is an entry field that you can use to enter the path to a file that you want to compare.

To compare two images, you can type the paths of two image files into the entry fields or use the buttons on the right-hand end of the entry fields to choose files to compare.

The Browse button opens a file-browsing window and the Show history button displays a list of the files that you have recently compared. Double-click a row in the list to load and compare the relevant files. Alternatively, hold Ctrl and double-click a file in the list to load only a single file.

If there are other versions of the file named in the entry field available for comparison in a version control system repository, the Versions button displays a list of these other versions. If this button is not enabled, check the relevant options on the Application and Credentials options pages.

To perform the comparison once you have chosen the two image files to compare, click the Start or recompare button in the ribbon, or press the Enter key while one of the filename entry fields has focus.

You can also drag and drop files from File Explorer on to the filename entry fields or on to the file panes.

Three-way file comparisons

In addition to two-way file comparison, the Professional Edition of Merge enables you to compare (and, for text files, merge) three files. Please see the Three-Way File Comparison and Merging topic for more information. The Professional Edition also supports the automatic merging of text files.

The image comparison display

Two sample image files (Test1.png and Test2.png) are provided in the Merge installation directory. The following screenshot shows the results of a comparison between these two image files.

Results of comparing test1.png and test2.png

The control strip at the bottom of the image comparison window enables you to customize the appearance of the comparison results. The screenshot below shows the above image comparison, but with only the changed pixels visible.

Results of comparing test1.png and test2.png, with only changed pixels visible

Show unchanged pixels

Toggles the display of unchanged pixels. When unchanged pixels are not displayed, the chequered transparent background is shown in their place.

Show changed pixels

Toggles the display of changed pixels. When changed pixels are not displayed, the chequered transparent background is shown in their place.

Highlight changed pixels

Highlights changed pixels by altering their colour. Repeated clicks on this control will cycle between off, and two different highlighting styles.


This slider control can be used to blend the compared images together on top of one another.


This slider zooms the compared images. It has discrete positions for 1×, 2×, 4×, 8×, 16×, and 32× magnification.

The Ctrl+= and Ctrl+- shortcuts can also be used to increase and decrease the image magnification respectively.

Information The current magnification is displayed to the left of the slider.

Layout controls

You can use the Two-way (horizontal) or Two-way (vertical) buttons in the ribbon (or the F11 and F12 keys) to change the layout of the files within the file comparison window so that the compared files are displayed one above the other or side-by-side (the default).

There are many options that you can set to customize how Merge compares and displays files. There are help topics that will enable you learn how to customize Merge so that it produces the best results for you.

As you scroll one file up and down using its scroll bar, the other file is scrolled so that the two files remain aligned. You can temporarily prevent Merge from keeping both files aligned by holding down the Ctrl key whilst scrolling. When you release Ctrl, the files will snap back into alignment.

Mouse navigation

Merge supports mice with wheels. If you have a three-button mouse, you can click within a file panel with the middle mouse button to enter a panning mode. The file will scroll in the direction you move the mouse. To stop panning, click the middle mouse button again. If your mouse has a wheel, you can use it to scroll up and down within the active file.

Switching between multiple file comparisons

Merge allows you to work with multiple file comparisons open at the same time. A tab strip along the top of the main file comparison window allows you to switch between file comparisons with a single mouse click.

Supported file formats

Format File extensions
CompuServe Graphics Interchange Format *.gif
JPEG - JFIF Compliant *.jif;*.jpeg;*.jpg
Portable Network Graphics *.png
Tagged Image File Format *.tif;*.tiff
Windows or OS/2 Bitmap *.bmp,*.ico
DirectDraw Surface *.dds
Digital Negative *.dng
Windows Media Photo *.wdp
Canon Raw Image *.cr2