Today’s Question: How does the Trim command in Photoshop relate to the Crop tool?
Tim’s Quick Answer: The Trim command is similar to the use of the Crop tool in that it allows you to crop the photo. However, with Trim you are cropping in an automatic fashion based on pixel values found at the edge of the photo, rather than making a specific choice about how to crop the image.
More Detail: When you use the Trim command (found on the Image menu) you are able to choose how to automatically crop the image based on pixels along the edge of the image. If there are transparent pixels along the edge of the image you can choose the “Transparent Pixels” option in the Trim dialog to crop the image to bring all four edges of the image in to the first non-transparent pixel on each side.
You can also choose to trim the image based on the color of the top left or bottom right pixel. For an actual photographic image this would obviously not be very helpful, since each pixel is likely to have at least some degree of variation. So this is more useful for things like screen captures or graphics. For example, if you had a graphic set against a white background, you could use the Trim command to crop all of the “outside” white pixels so that the edge of the image aligned with the edge of the graphic.
Note, by the way, that you do have the option to choose which edges you actually want to trim, with the Top, Bottom, Left, and Right checkboxes. Ultimately, however, the Trim command is mostly helpful for screen captures, graphics, and certain composite images.
It is also important to be aware that the Trim command takes a destructive approach, whereas the Crop tool allows you to take a non-destructive approach to cropping. With the Crop tool you can choose to disable the “Delete Cropped Pixels” checkbox on the Options bar, so that when you crop you are really just reducing the canvas size and hiding the cropped pixels. Those hidden pixels can then always be revealed with the “Reveal All” command found on the Image menu. The Trim command, by contrast, crops by actually removing the trimmed pixels from the image.