Submitting images › About image quality
About image quality
Depending on what kind of image you wish to submit, please think about your format and quality carefully. Designers working with photographs for print usually prefer 300dpi *.tif or *.psd (Photoshop) images over *jpg. This is because *.jpg is a compressed format. Photographs straight from a digital camera are almost always saved in *.jpg format at 72dpi. This doesn’t mean they aren’t good enough for print, but how then do you judge them? Please read on.
Resolution vs Size
This photo is 300 pixels wide and 200 pixels high (its size). It has a resolution of 300 dpi.
This is equal to 1 inch wide, 0.667 of an inch high and a total of 60,000 dots (or pixels) in the image.
Photo by Andrew Lamb
When creating or editing graphics, it’s important to understand the difference between resolution and size.
Size in this case refers to the dimensions (height and width) of the image, which you can determine in most image viewing and editing programs. In Windows, you can usually see the height and width of an image when you have it selected.
Resolution is primarily defined by how many ‘dots’ there are per inch (DPI). This affects quality, especially for printing. Magazines and books will usually only print high quality images with 300 dpi. However, it is very common for designers to convert 72 dpi photos to 300 dpi, when they are large enough (in size) and sharp enough (in quality). Website images are usually 72 dpi because this makes the file-size (how many bytes or kilobytes the image takes up on your computer hard-drive) smaller and you won’t even notice the difference on-screen.
Quality is generally a judgement call based on what the image looks like when it is printed or when you zoom in on it. You can have an image with very high resolution and very large size that is poor quality. Some photographs, for example, were simply taken in poor lighting and will be beyond repair.
If you can extract small parts of an image and it is still relatively clear, then the image is probably good quality. The size and resolution will also be factors to consider. The image above, for example, is a thumbnail of a stock photograph with a resolution of 300 dpi and dimensions (size) of 4072 x 2712 pixels. Basically, this photo is massive. The yellow section above can be cut out of the full-sized image and reduced to 300 pixels wide and still look good. See right.
One property of poor quality images are ‘artifacts’. If I want to print the red-outlined section in image A below at a size of 4 inches wide, then I have to stretch it. But, because it is poor quality, I will see artifacts when I stretch it. See arrow on image B. Although you may not notice these artifacts on the screen or on the web (without zooming in), they may be visible if printed in a magazine.
So ultimately, quality comes down to a judgement call based on what the image is being used for and how it looks when you print it and/or zoom in on it. It is better to err on the side of caution and set a high standard for images, always trying to get the highest resolution, size and quality as possible. All three must go hand in hand.