About image size and resolution

The image size (or pixel dimensions) of an image is a measure of the number of pixels along an image’s width and height. For example, your digital camera may take a photo that is 1500 pixels wide and 1000 pixels high. These two measurements indicate the amount of image data in a photo and determine the file size.

Resolution is the amount of image data in a given space. It is measured in pixels per inch (ppi). The more pixels per inch, the greater the resolution. Generally, the higher the resolution of your image, the better the printed image quality. Resolution determines the fineness of detail you can see in an image.

Although a digital image contains a specific amount of image data, it doesn’t have a specific physical output size or resolution. As you change the resolution of an image, its physical dimensions change, and as you change the width or height of an image, its resolution changes.

About image size and resloution
Two images (A and B) with same image data and file size but different image size and resolution; C shows that a higher resolution means better quality

You can see the relationship between image size and resolution in the Image Size dialog box (choose Image > Resize > Image Size). As you change one value, the other two values change accordingly.

Image size options
Constrain Proportions lets you change image size without altering any image data

The Constrain Proportions option lets you maintain the aspect ratio (the ratio of image width to image height). If you select this option and change the image size and resolution, the image does not stretch or shrink.

The Resample Image option lets you change the size of an image without changing the resolution. If you need to print at a specific resolution, or at a smaller or larger resolution than the current image allows, resample the image. However, resampling can degrade image quality.

About monitor resolution

Your monitor’s resolution is described in pixel dimensions. For example, if your monitor resolution is set to 1600 x 1200 and your photo’s pixel dimensions are the same size, at 100%, the photo will fill the screen. The size an image appears onscreen depends on a combination of factors: the pixel dimensions of the image, the monitor size, and the monitor resolution setting. In Photoshop Elements, you can change the image magnification onscreen, so you can easily work with images of any pixel dimensions.

About monitor resolution
A 620 x 400‑pixel image displayed on monitors of different sizes and resolutions

When preparing images for onscreen viewing, you should consider the lowest monitor resolution that your photo is likely to be viewed on.

Display the image size of an open file

  • Click-hold the file information box at the bottom of the document. The box displays the width and height of the image (in pixels, and in the unit of measurement currently selected for the rulers), the number of color channels, and the image resolution (ppi).

View the print size onscreen

  • Do one of the following:

    • Choose View > Print Size.
    • Select the Hand tool or Zoom tool, and click Print Size in the Tool Options bar.
    • The magnification of the image is adjusted to display its approximate printed size, as specified in the Document Size section of the Image Size dialog box. Keep in mind that the size and resolution of your monitor affect the onscreen print size.

Change print dimensions and resolution without resampling

You might need to change the print dimensions and resolution if you are sending the image to a print shop that requires files to be at a specific resolution.

If you are printing directly from Photoshop Elements, you don’t have to perform this procedure. Instead, you can choose a size in the Print dialog box and Photoshop Elements applies the appropriate image resolution.

Note:

To change only the print dimensions or the resolution, and adjust the total number of pixels in the image proportionately, you must resample the image.

  1. Choose Image > Resize > Image Size.

  2. Make sure that Resample Image is deselected. If deselected, you can change the print dimensions and resolution without changing the total number of pixels in the image, but the image may not keep its current proportions.

    Note:

    Resample Image must be selected in order to use the Constrain Proportions and Scale Style functions.

  3. To maintain the current aspect ratio, select Constrain Proportions. This option automatically updates the width as you change the height, and vice versa.
  4. Under Document Size, enter new values for the height and width. If desired, choose a new unit of measurement.

  5. For Resolution, enter a new value. If desired, choose a new unit of measurement, and then click OK.

    Note:

    To return to the original values displayed in the Image Size dialog box, use Alt (Option in Mac OS) + click Reset.

Resample an image

Changing the pixel dimensions of an image is called resampling. Resampling affects not only the size of an image onscreen, but also its image quality and its printed output—either its printed dimensions or its image resolution. Resampling can degrade image quality. When you downsample, meaning that you decrease the number of pixels in your image, information is removed from the image. When you upsample, or increase the number of pixels in your image, new pixels are added based on the color values of existing pixels, and the image loses some detail and sharpness.

To avoid the need for upsampling, scan or create the image at the resolution required for your printer or output device. If you want to preview the effects of changing pixel dimensions onscreen or print proofs at different resolutions, resample a duplicate of your file.

Resampling an image
Resampling an image

A. Image downsampled B. Original image C. Image upsampled 

Note:

If you’re preparing images for the web, it’s useful to specify image size in terms of the pixel dimensions.

  1. Choose Image > Resize > Image Size.

  2. Select Resample Image, and choose an interpolation method:

    Nearest Neighbor

    Fast, but less precise. This method is recommended for use with illustrations containing edges that are not anti-aliased, to preserve hard edges and produce a smaller file. However, this method can create jagged edges, which become apparent when distorting or scaling an image or performing multiple manipulations on a selection.

    Bilinear

    Medium-quality.

    Bicubic

    Slow, but more precise, resulting in the smoothest tonal gradations.

    Bicubic Smoother

    Use when you're enlarging images.

    Bicubic Sharper

    Use when you’re reducing the size of an image. This method maintains the detail in a resampled image. It may, however, oversharpen some areas of an image. In this case, try using Bicubic.

  3. To maintain the current aspect ratio, select Constrain Proportions. This option automatically updates the width as you change the height, and vice versa.
  4. In Pixel Dimensions, enter values for Width and Height. To enter values as percentages of the current dimensions, choose Percent as the unit of measurement.

    The new file size of the image appears next to Pixel Dimensions, with the old file size in parentheses.

  5. Click OK to change the pixel dimensions and resample the image.

    Note:

    For best results in producing a smaller image, downsample and apply the Unsharp Mask (Enhance > Unsharp Mask). To produce a larger image, rescan the image at a higher resolution.

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