Image cropping: the easiest picture editing action that you might be doing wrongly!

Cropping= cutting a picture from sides. It is like using a scissors to cut a photo print from one or more sides.

tool is available on all image/ photo editors and mobile image apps. It is there even in the basic 'gallery' or 'photo' apps on mobile phones and in the camera app. 

Most users of digital images use this tool, but the irony is that not many understand how this tool impacts the image, and the best way to crop images.

If you are interested in going into the details of how different image editing tools work, I would refer you to Better Digital Images, my ebook on digital image editing and digital photography. I give here some basics of cropping:

Cropping of pictures leads to change in their properties

Cropping is done basically to remove objects from the sides, thus also reducing the size of an image. But remember that cropping affects the image in many more ways than cutting the sides of a photo print. Look at these concepts:
  • Cropping removes some objects from the image. Because of this, cropping is usually carried out to frame the pictures better. 
  • Cropping reduces the size of the image in terms of pixels. So, if an image is of 5  MP (megapixel) size and you cut it from the middle, the resultant pics would be 2.5 MP each. 
  • It can change the aspect ratio of the picture. Aspect ratio is the ratio between the width and height of the picture. If you have a wide image of 5 inch x 3 inch size and remove 2 inch from one side, the resultant image would now by a square image of 3 inch on each side. 
  • Cropping can reduce the quality of picture if you crop the picture and then pull it to the original size. Suppose you have a picture of 10 inch x 6 inch size and you cropped it into 5 inch x 3 inch to remove some peripheral objects. Now if you want to make this picture again of 10 inch x 6 inch, it will pull the pixels and add new pixels into the image; thus, the resultant picture would suffer a quality loss. 
  • It can distort the picture if you crop the image not in the original aspect ratio and then try to fit it into the original aspect ratio or an altogether different size. For example, you cropped a 6 inch x 6 inch image by removing different sized areas from height and width, the resultant pic will no longer be a square image. If you try to fit it into any shape other than a sqaure, it will get distorted. 

How to use cropping tool the best way in a photo editor

With the above understanding let us use cropping wisely, as follows:

Crop images for better framing and removing unwanted objects. 

When you shoot a photograph, you sometimes do not see a disturbing object till it shows up in the photograph. You would definitely like to remove it from the photograph without artificially manipulating it. Or you have a group photograph out of which you want to frame a part in which only you and your best friend standing next to you are seen. Or you took a photograph of your child in which the background is too overbearing and the child's pic is lost in it - you would like to remove most of the background so that the child comes out prominent. 

Think of the final size of picture before you begin cropping it. 

If by cropping the photo too much, the remaining part would remain like a small stamp, it would not look clear. On mobiles and computers/ laptops, the image viewers often expand small pics to the size of the app/ device: if so, the small picture would look too bad in clarity and contrast. So, crop a picture only as much is required.

Think of the final aspect ratio of picture beforehand. 

If you cut out one side of the photo or other image, the original aspect ratio would change. Therefore, if you need to cut from width, cut from the height also in the original ratio. Most apps show the crop tool with brackets in the corners of the picture (please see the C image below). If you slide these corner brackets, the cropping will preserve aspect ratio. 

Use the crop tool before resizing the picture. 

If you have to reduce the size of the picture, one way is to squeeze it to the new size. But any reduction (or enlargement) of picture leads to decline in quality. So, when you need to reduce the size of the picture, think of cropping it first, before resizing so that you will need less squeezing of the picture. However, you should do this only if removing object from the original picture will not harm the picture.

How does cropping actually affect a picture?

For more clarity, I will illustrate the concept of cropping with the help of a picture: 

Look at the collage of 4 images given here.  Let's see the first one on the left: it is the original one. It has two hills, a tree and something at the right bottom, which is spoiling the image. 

image cropping and resizing

Now look at A. We wanted to remove the disturbing object and cropped the right portion of the image. Now the earlier wide image has become less wide. We must crop some height too so if we want to retain the original aspect ratio, as shown in C.

But we may want to create an image out of the original, which has aspect ratio like A (=less wide) but we would like to retain the object. One way is to resize the image with the new width. When we do that, the shapes of trees and hills get distorted like B. This is not desirable.

In C, we see the corner brackets that can be pulled to crop the image in the original proportion. If we click on the corner where C is written and pull the cursor inward, a new area can be seen that has less height and width in the same aspect ratio as the original image.

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