Retouching and Editing

Cropping and Trimming Images

With cropping and trimming, an area of an image is defined and then the rest of the image is deleted or hidden, resulting in new image dimensions. This lecture covers the Crop tool, Crop command and Trim command.

Cropping With the Crop Tool

Crop tool The Crop tool offers the most options for cropping an image. Before you crop, you can set the resolution and dimensions of the resulting cropped image. After you define the area you want to crop to, you can adjust its size, move or rotate it, apply perspective, and set whether to hide or delete the remainder of the image.

Practice Exercise: Using the Crop Tool

  1. Open Cat.psd.
  2. Select the Crop tool. Drag to create a marquee around the cat as shown below. Notice that once you release the mouse button, a crop marquee appears around the selection and the area outside the marquee is darkened by what is called the crop shield. This helps you visualize what the cropped image will look like.

drawing the crop marquee

  1. To finish the operation, press Enter (Return) or click on the Commit button in the Tool Options bar.

The image window will become the same size as the crop border that you created. Because the image is on a Background layer, the Cropped Area: Delete/Hide options were unavailable. You'd have to convert the layer to a regular layer before you could use that option. Let's try that.

  1. Double-click on the Background layer in the Layers palette. Click OK in the New Layer dialog.
  2. Create another crop marquee around the cat.
  3. Set the Cropped Area option to Hide.
  4. Press Enter (Return) or click on the Commit button to apply the crop.
  5. Switch to the Move tool and drag the image around in the window. You should be able to see that the areas remaining after the first crop are still available.
  6. Select the Crop tool and draw another crop marquee. Place the pointer inside of the marquee and move the marquee around.
  7. Disable the Shield cropped area option to see what happens. Turn it on again. You can change the colour and opacity of the crop shield with the Colour and Opacity controls.
  8. Click on the Delete option and then apply the crop. Use the Move tool to confirm that the cropped areas were deleted.
  9. Restore the original image by using the Revert command or the History palette. Convert the Background layer into a regular layer.
  10. Select the Crop tool again. In the Tool Options bar, type a Width of 175 and a Height of 375. Draw a crop marquee in the image and position it so it includes the cat's head. You'll notice that the dimensions of the marquee are constrained but you're able to draw it larger than the dimensions you entered. Once you apply the crop, the image will scale down to the Width and Height you specified.
  11. Apply the crop to see the result.
  12. To clear the values you set in the Width and Height fields, click the Clear button.
  13. Undo the crop.
  14. Make another crop marquee. Using the Info palette's W and H readout to help you, drag on the side handles to scale the marquee to 200 pixels wide by 300 pixels high. Move the marquee so it frames the cat's head and foot.
  15. Enable the Perspective option in the Tool Options bar. When you hold the pointer over a corner handle of the crop marquee, the Perspective pointer is displayed. You can drag the corner handles freely and independently to apply perspective or distortion.
  16. Drag the top handles outward. Holding the Shift key while doing so will constrain the movement to horizontal or vertical.
  17. Apply the crop.

crop marquee with Perspective applied and the resulting image

The irregular shape of area within the crop marquee was resized to create a rectangular shape which resulted in the distortion in the final image.

Front Image
This option can be used when you want to crop one or more images to the same pixel dimensions as another open image. When you click on the Front Image button, the dimensions of the current image will populate the W and H fields. Then you can switch to another document and apply those values to the crop.
This option would be handy if the image you're starting with is at a higher resolution that 72 ppi. You can both crop and resample in one step.

Cropping With the Crop Command

To use the Crop command, an area of an image must first be defined by a selection marquee created with one of the marquee tools. The logical choice would be to apply a rectangular marquee but the command will work with oval or irregular selections too.

Practice Exercise: Using the Crop Command

  1. Undo the Perspective crop you made in the last exercise.
  2. Use the Rectangular Marquee tool to make a selection of the cat.
  3. Go to Image > Crop.
  4. Undo this action.
  5. Use the Elliptical Marquee tool to make a selection.
  6. Go to Image > Crop. The image was cropped to the selection border of the oval shape. If you shift the image with the Move tool, you'll see that the excess parts of the image were deleted. There is no Hide option with the Crop command.
  7. Close your file without saving it.

Using the Trim Command

The Trim command will trim off excess transparent areas from an image. It can also trim based on a pixel colour.

Practice Exercise: Using the Trim Command

  1. Open Cat_extract.psd. This image has excess transparency that we can use to practice the Trim command.
  2. Go to Image > Trim and the Trim dialog will open.

Trim dialog

The Based On options are used to set the method of trimming. The Trim Away section of the dialog lets you specify the sides of the image you want to be trimmed.

  1. Match your settings to the ones in the example above and click OK. Your image should look like the one below.

trimming based on transparency

  1. Undo this step.
  2. Duplicate the layer and use the Move tool to shift a copy of the cat layer so you can see both cats.
  3. Repeat the Trim command. This will use the opacity of both layers to set the amount of trimming.

trim based on transparency of two layers

  1. Hide one of the cat layers and trim again.

The trim was made based on the transparency of the visible pixels. The transparency of hidden layers is ignored.

  1. Close your file without saving it.

Trim Based on Pixel Colour

These options could be useful for trimming off strips of colour that appear around an image, such as on scanned images.

trim based on top left pixel colour

The image above is a very elementary example of what this option can do. The Trim dialog was set to Based on: Top Left Pixel Colour which, in this case, is green. There are strips of the colour along the top and left. Once the command is executed, the green was trimmed, leaving only the black area.

Cropping and Trimming Images Summary

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