A crop is a making a rectangular selection in a photograph. This could be a compositional adjustment of the photograph or fine tuning the shape to fit a display medium. Cropping is useful for candid and action shots where there are compositional aspects beyond the photographer’s control.
There are a number of reasons why it is difficult to always compose the photograph perfectly in the camera. It could be there is no time to move to a position frame the photograph exactly, or it may be physically impractical. Especially when the distance from the subject does not match the focal length if you are using a prime lens, but also when you run out of zoom.
For action shots often there is no time to carefully frame a fast moving event in the viewfinder, the main object is making sure you capture all the important elements of the subject. The old compositional adage is to “fill the frame” but you do need to take care not to overflow the frame.
Even in nominally static landscape photography, time can be critical as the changing light will not wait. So you have to shoot when an opportunity presents itself, often depending on the angle of the sun and breaks in cloud cover.
Software editing apps, such as Adobe Lightroom, only present a preview of the changes to the user. Any changes are not made to the original photo file, but are applied when a copy is created or a print is made. This allows photographers to improve their composition skills by experimenting with cropping adjustments to photos.
The lessons learned using the cropping tool can be applied to future photographs to minimise the need or extent of any cropping required. Keeping cropping to a minimum preserves resolution because every time you crop part of a photograph you lose resolution or a number of megapixels from the photograph. High-resolution digital cameras make this less of a problem it is still better to preserve as much detail as possible.
Large bodies of water, such as lakes and seas, produce a flat horizon. Most buildings have vertical orientation rather than leaning to one side.
One of the important jobs of the crop tool is to choose the section of the image from the original photograph to a different aspect ratio print or screen size. The relationship between the width and height of an image is the aspect ratio.
Photographs are displayed using a wide variety of shapes. Even the humble print has a range of paper sizes with slightly different shapes and then there are device screens. I have a number of computers each with a different shape and size screen. This also applies to cameras, where the width and height of the film, or digital sensor, varies.
Using Lightroom crop tool
The basic crop tool is an adjustable rectangle superimposed on the image shown in Lightroom’s preview window. To adjust the size of the crop box drag it by one of its edges.
When the padlock icon in the crop menu is closed the crop box uses a fixed aspect ratio where dragging one side also moves the adjacent side as well. If the padlock is open then the side being dragged moves independent of the adjacent sides. This changes the aspect ratio as well as the size of the selection.
This technique is useful when there is flexibility in the display format and the best composition does not match the aspect ratio of the camera.
The Adobe Lightroom crop tool menu has a number of standard aspect ratios for common print and screen sizes. Then there is an option to add a custom aspect ratio for the pop-up list.
The Lightroom crop tool selection overlay has Rule of Thirds guides to help make adjustments using this compositional guide.
The Straightening tool has a number of options for rotating the crop box. There is an auto function where Lightroom analyses the photograph and estimates the proper horizontal angle. Also, there is an angle slider for adjusting the horizontal angle by dragging the slider or specifying a numerical value.
Pro Tip: use the up and down arrow keys to alter the numerical value of the angle in small steps.
If you move the pointer outside the crop box corner then the pointer changes to a double-ended arrow, indicating the crop box is in rotate mode. Then click and drag the pointer to alter the angle of the crop box.
The spirit level icon allows you to draw a line on the image to match a horizontal or vertical object and Lightroom uses that as a reference to straighten the crop box image.
It is easy to move the crop box around the image in the preview window. Move the pointer inside the selection area and when the pointer changes to a hand to drag the crop box to a new position on the image.
Cropping is necessary after Lightroom tools to correct the perspective of apparently tilting tall buildings. If you tick the “constrain to crop” option in the crop panel then Lightroom automatically crops the image to fit.