How do I change the resolution of an image?

Resolution of a photo refers directly to the size of your image. This means more than just its physical size in inches, but also the number of pixels per inch. This is important because if there are not enough pixels or a high enough resolution your image will appear low quality or grainy in your final project. The good news is that changing the resolution of an image is a simple task.

The Vocabulary
When changing the resolution of a photo, you should start by taking note of the terms you’ll be seeing and how each applies to your project. In general, you’re likely to see two key terms: pixel dimensions & image resolution.
 
Pixel Dimensions- This term relates to the number of pixels along the width and height of your image.
 
Image Resolution- This term relates to the fineness of pixels in the allotted space. This number is measured in pixels per inch, or ppi. The higher the ppi, the higher the image resolution. In general, a larger ppi will equate to a sharper, higher quality printed image.
 
Finding the Appropriate Resolution
Before altering your image or project, you’ll first want to know exactly what ppi you need. This is a task that is quickly and easily completed within Photoshop. You will need to know screen frequency of the output device- your printer or the screen on which your project will be viewed. In order to get an appropriate resolution, simply follow these steps:

  • Choose Image > Image Size.

  • Click Auto.

  • For Screen, enter the screen frequency for the output device. If necessary, choose a different unit of measurement. The screen value is used only to calculate the image resolution, not to set the screen for printing.

  • For Quality, select an option:

    • Draft -Produces a resolution that is the same as the screen frequency (no lower than 72 pixels per inch).

    • Good- Produces a resolution 1.5 times the screen frequency.

    • Best- Produces a resolution 2 times the screen frequency.

If you choose an image over 2.5 times the screen frequency it will display a warning message and may not allow you to proceed.

How to Make the Change
Unless you’re using a resampled image- one that has image data that has already been changed- an image will also change its size as you increase the resolution. Photo editing programs like Photoshop will make all of this data easily visible to you in the “Image Size” dialog box. When you change one element of the image the others will automatically adjust in order to keep your image in proportion and with appropriate ppi. You can override the automatic updating by selecting the “resampled” option. While this does give you greater flexibility to fine tune your ppi and sizing needs, it can also lead to images that are out of scale and should be used carefully.
 
Here are the steps for changing your resolution:

  • Choose Image >Image size

  • Maintain the current ration to pixel width to pixel height by selecting “Constrain Proportions”

  • Under “Pixel Dimensions” enter your new values. To enter values as a percentage, you can select “Percent” as the unit of measurement.

  • Ensure that “Resample” is selection and choose an interpolation method

  • If your image has layers with styles applied to them, select Scale Styles to scale the effects in the resized image. This option is available only if you selected Constrain Proportions.

  • When you finish setting options, click OK.

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