Store development snapshots and compare with the current edit.
A snapshot is a stored bitmap of the center image in the darkroom view. Snapshots can be taken at any point in the development process and later overlaid onto the current center view. This allows you to undertake a side by side comparison (by default left=snapshot, right=active edit) while you are tuning parameters of a module. This can also be combined with the history stack module to compare a snapshot against different stages of development.
To take a snapshot, click on the take snapshot button. Above the button you will see a list of the snapshots that have been taken for this editing session. The name of each snapshot reflects the name of the module selected in the history stack and its position at the time the snapshot was taken.
Click on the name of a snapshot to show it – this enables a split view between the saved snapshot image and the current state of the processed image. You can control the split view by moving the splitline back and forth over the image with your mouse. If you hover over the splitline with your mouse, a small rotation icon will appear on the center of the line. Click this icon to change between vertical and horizontal split view.
At all times, an arrow containing the letter “S” is displayed to indicate which side of the image is the snapshot and which is the current edit.
Click on the name of the snapshot again to disable the overlay and return to your editing session. Click the module’s reset button to remove all existing snapshots.
Note: Snapshots are retained for the duration of your darktable session. This means that you can also use snapshots to compare with a duplicate edit of the same image. Just navigate to that image and enable the snapshot view as normal.