Batch Adjustments - Sync
RawTherapee lets you batch-adjust, or sync, the processing settings in many photos at the same time in generally two ways. It lets you copy and paste a processing profile (a collection of tool settings), in parts or in full, to any number of images. It also lets you select any number of images and adjust any tool in all of them at once (sync), and it lets you do this in two ways. Let's take a closer look.
Both ways involve making a selection of photos you want the processing profile or adjustments applied to. Selections are made using standard key combinations: Shift+click to select a range, Ctrl+click to select individual images, or Ctrl+A to select everything. Both ways are performed from the File Browser tab. The "copy & paste" method can also be done via the Filmstrip.
Copy & Paste
Copying and pasting a processing profile to a selection of images is a very common task. Assume you took a series of photos - for example studio shots, wedding portraits or focus-bracketed macro photos. All images in each series are going to be very similar; they will probably use the same lens, the same ISO, the same white balance, and end up being used for the same purpose. This means that they will all probably require the same processing settings - the same noise reduction, the same sharpening and lens distortion correction, and so forth.
To process the lot, what you would usually do is open any one image from the whole series in the Editor tab and tweak it to your liking. Once you have finished tweaking it, you will apply this image's processing profile to all other images in the same series. To do that, go to the File Browser tab, right-click on this photo and select "Processing Profile Operations > Copy", then select the images you want to apply this profile to, right-click on any one of them (it doesn't matter which) and select "Processing Profile Operations > Paste". In one quick operation you have replicated the same tool settings in the whole series of images.
Additionally, RawTherapee lets you apply only a part of the copied processing profile, for example only the "Resizing" tool. To do this, use the "Processing Profile Operations > Paste Partial" option instead of the "Paste" option.
RawTherapee lets you instantly apply tool adjustments to a selection of images. Similar functionality in other software is called "sync". This method is useful for when you don't need to see an accurate preview of your changes, for example when you only want to enable the "Resizing" tool in a selection of photos, because when working in the File Browser tab your only preview are the small and inaccurate thumbnails. This method can only be performed from the File Browser tab because you need access to that tab's batch tools (the panel on the right).
When you're in the File Browser tab, select the images you want to batch-adjust (sync), then use the tool panel on the right to make adjustments. Your tweaks can either replace the existing ones ("Set" mode), or be added to them ("Add" mode). For example if you select two photos, one of which has previously been tweaked with +1EV Exposure Compensation and one which has not, and you set Exposure Compensation to +0.6EV, then the previously-tweaked photo would end up having +1.6EV Exposure Compensation in "Add" mode and just +0.6EV in "Set" mode. The photo which was not previously tweaked would have +0.6EV in both modes. You can decide which tools should work in which mode from the Batch Processing tab in Preferences.