This article is for those who need help deciding if and how to resize their digital images. It is not a comprehensive tutorial, it is meant to help someone decide what to do if they are asked for a high-resolution image to be printed in a catalogue, for example.
- to speed up the display of your image on websites and social media, especially when viewed on mobile devices
- to reduce the size of the documents in which the images are embedded
- to comply with submission guidelines for web or printed images
- to avoid overwhelmed the email system when sending many attached images
- to control the size and quality of the image as it will appear on the web or print
Do I really need to resize?
Do not resize your original images. Always make a copy of your original image, and resize the copy.
For posting images online, not really. Most web / social media platforms take care of this for you. If you want “pixel perfect” images, you will want to resize for specific platforms. These sizes are well publicized on the web.
For print, you need to ensure that the size of your image is big enough so it won’t print fuzzy. Read on to find out how.
What do you mean by "image size"?
Digital images are a mosaic of tiny color dots called pixels. The more pixels an image has on the horizontal and on the vertical, the “smoother” it will look on the computer screen or on the printed page.
image size = number of horizontal pixels by number of vertical pixels
For example, an image may have 960 pixels on the horizontal and 699 on the vertical. The size is 960 by 699 pixels, or 960 x 699 pixels. Your computer will tell you the number of pixels for each image.
What about DPI or megapixels?
DPI stands for "dots per pixel" and is a characteristic of printers, not your image. When creating a physical print of an image, the size of the print will be the size of the image (in pixels) divided by the DPI of the printer. Most printer's DPI is 300; an image of 3000 x 3000 pixels, when printed on such a printer, will result in a 10 inch by 10 inch physical print (3000 pixels divided by 300 dpi equals 10 inches).
Megapixels is a measure of the total number of pixels are in the image (width in pixels multiplied by height in pixels). This measure is virtually useless to you.
What is a "High Resolution" Image?
There is no universal definition for "high resolution", so here's mine:
1. For images to be viewed on the web, or a computer monitor, a high resolution image will have more than 900 pixels on its shortest dimension
2. For images to be printed, a high resolution image will have at least 300 times more pixels on each dimension than the intended print size, in inches. As an example, for a printed image of 2 inches by 2 inches, any image that has 600 (2 inches x 300 dpi) or more pixels on each direction is considered high resolution.
How do I resize?
You will need a tool to do the resizing. There are several available both as software installed on your computer (e.g., Photoshop Elements), or websites (e.g., http://resizeimage.net/). Find the one that works best for you in terms of simplicity of use and feature set.
What size should I make it?
If it's a profile picture, most websites require a square image. Crop your image square and make it 400 pixels by 400 pixels. This size will work in most cases.
For all other images, make them 1600 pixels wide. If you are posting fine photography, make them 2500 pixels wide.
Determine the exact size of the image on the physical print, in inches. If that's not possible, find out what the largest size could be. For example, if you know that the image will be printed on a brochure that is 8 inches wide by 10 high, the maximum width of your image is 8 inches.
Multiply the width and the height of the image on the physical print by 300 (in rare cases 600, for extremely high quality prints, ask your printer). This will give you the minimum size of the digital image, in pixels.
If your image is larger that the minimum size determined above, you may choose to resize it, otherwise it will be resized for you when the printed product is laid out.
If your image is smaller than the minimum size (fewer pixels on the horizontal or vertical), the resulting printed image will be fuzzy. The only solution to this problem is to print the image smaller (size of the print = size of image in pixels divided by 300)