Image Sizing


Image Sizing

What is image sizing?

Image sizing and resolution selection can be confusing and are often misunderstood by many students.  It is also often overlooked and not regarded as that important. However, if a beautifully photographed image that is also retouched really well is submitted at a wrong resolution it simply can not be accepted or printed.  So all that work goes to waste.  By submitting an image that is appropriately sized for its purpose you are assured that it will be viewed, printed or published.  In this tutorial we will look at the different settings needed for supplying images for print and for web.

How to resize an image?

There are key points to consider when resizing an image.  Firstly lets understand the two main resolutions and uses of a digital image. Digital images are mainly used for print or web with each needing a different resolution.  If you print an image then the image resolution needs to be 300 dpi. If you are placing an image on a website or emailing it to someone to only be viewed on screen then the image resolution needs to be 72 dpi.  It isn’t as simple as altering the resolution because you also need to take into consideration the pixel dimensions. This is done by using an option called ‘Resampling’.  If you reduce the resolution from 300 dpi to 72 dpi and do not resample the image then your image may turn from 30 cm to 2 meters wide so you must be taking note of the pixel dimensions.  It is best to see this in action, lets look at the interface of the image sizing panel then we will look at a short video explaining this further.

Image sizing interface in Photoshop.

Image sizing panel

To open the image size panel in Photoshop go to the pull down menu ‘Image’ and then select ‘Image Size’ option. In the image size panel we can see several very important settings:

  • Image Size – This will not be the actual saved image size. To see the actual image size you will need to select the image in your finder once you have adjusted and saved it as a copy.  If the image has smart objects or many layers then even though the file may be small in terms of its dimensions it may be taking up a large amount of space.  This is often misunderstood so please take close attention to each point I have just outlined.
  • Dimensions – This is the physical size of your image, when re-sizing (resampling) this will change.  If you are not resampling then the actual size of the image will not change.
  • Fit to – In here you can find some pre set sizes.
  • Width and Height – The default is set to centimetres but that can be changed to display inches or pixels. The lock that appears to link the Width and Height indicates that if you change one then the other will also change – constraining proportions.  Altering width and height is useful when you need to change the size of your file to fit a specific size.  For example you need an image to be printed at 10 inches by 8 inches.  Here you can make that alteration.
  • Resolution – This is where you can alter the resolution of your image.  72 pixels/inch is for images that will be seen on the web and 300 pixels/inch will be for an mage that will be printed.
  • Resample – This option is ticked by default.  This means that if you make any changes to the dimensions or resolution then the size of the actual file will change.  Be careful not to make the file larger.  A rule to follow is that you can make a large file smaller but you can not make a small file larger.  If you do then this is called interpolation.  This will result in a loss in image quality and make the image unusable.

Lets watch this in action.