The only difference between the crop tool in RawTherapee and that in other programs is that the cropped-off area is never discarded - this means that once you draw the crop you don't need to click any "OK" button to apply it - it's done. You will see the masked cropped-off area in the preview, but it will not appear in the saved image. Go to "Preferences > General > Crop mask color/transparency" to change the color and transparency of the masked area around the crop.
Activate crop-placing mode by clicking the "Select Crop" button in the tool panel, the button in the Editor's top toolbar, or the appropriate keyboard shortcut, then create the crop by clicking and dragging over the preview with your mouse. Use the Shift key to move the crop over the image. Resize a crop by placing the mouse on one of the sides or corners. To clear the crop, activate crop-placing mode again (via the keyboard shortcut or either of the buttons mentioned above), and click anywhere in the preview without dragging.
Use Guide Type to select popular guides to help you in composition while cropping, and a horizontal (landscape) or vertical (portrait) orientation. By default, as of version 4.2.214, RawTherapee automatically detects and uses the same crop orientation as the orientation of your image - the "As Image" option.
The PPI value does not change any physical property of the image, it only sets metadata which describes the intended print size of the current crop (or the whole photo if there is no crop). For prints up to 13x18cm (5x7 inch), 300PPI is a good choice; bigger prints can have less pixels per inch.
Use "Fix ratio" to set the crop to a fixed ratio.
- Classic negatives have this ratio, as do APS-C DSLR cameras.
- The Four Thirds System.
- The 1080p and 720p high-definition video format, and due to this the most common computer monitor aspect ratio since 2010.
- The most popular computer monitor aspect ratio between 2005-2009. Still popular in tablets.
- 24:65 XPan
- Hasselblad's medium-format cameras.
- 1.414 DIN EN ISO 216
- 1.414 DIN EN ISO 216 is the standard paper size ratio such as A4, B5, etc.
- The US Letter size.
- 11:17 - Tabloid
- A common tabloid newspaper format.
- 45:35 - ePassport
- Guides to help you crop a portrait for a biometric passport. Official measurements do not specify exact ratios, just min/max measurements within which the eyes and chin-crown distance must lie. The guides represent the averages of those distances. The first horizontal guide is for the crown, the second is roughly for the nostrils, the third is for the chin. "On the photo, the face must be between 29mm and 34mm from the bottom of the chin to the crown (the top of the head, not the top of the hair)." .