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How to Change Pixel Size in GIMP?

Published in Image Editing 3 mins read

You can't directly change the "pixel size" in GIMP in the way you might be thinking of enlarging individual pixels to make them visible. Instead, you adjust the image's resolution, which effectively changes how many pixels are displayed per unit of measurement (like inches or centimeters). This affects the print size of your image and how it appears on screen at different zoom levels. Here's how to do it:

Steps to Adjust Image Resolution in GIMP:

  1. Open your image: Go to File > Open and select the image you want to edit.

  2. Access the Print Size dialog: Go to Image > Print Size. This opens the "Set Image Print Resolution" dialog box.

  3. Adjust the Resolution: In the "Set Image Print Resolution" dialog, you'll see fields for "X Resolution" and "Y Resolution." These values represent the number of pixels per inch (ppi) or pixels per centimeter (ppcm).

    • Higher Resolution (more ppi/ppcm): Results in a smaller print size but potentially sharper details.
    • Lower Resolution (fewer ppi/ppcm): Results in a larger print size but may make the image appear blurry or pixelated if printed at a large size.

  4. Enter your desired resolution: Type in the desired X and Y resolution values. Keep in mind that if the "X Resolution" and "Y Resolution" values are linked (indicated by a chain icon next to the values), changing one will automatically change the other to maintain the aspect ratio. You can click the chain icon to unlink them if you want to set different resolutions for the X and Y axes.

  5. Click OK: Click "OK" to apply the changes.

Important Considerations:

  • Resampling: Changing the print size without resampling simply changes the metadata indicating the resolution. The number of pixels in the image itself remains the same. To actually change the number of pixels (and therefore potentially image detail or file size), you need to use the Image > Scale Image option. This process is called resampling, and it can either add pixels (upscaling) or remove pixels (downscaling). Upscaling can lead to a loss of sharpness, while downscaling can result in a smaller file size.

  • Resolution for Printing: A resolution of 300 ppi is generally recommended for high-quality prints. Lower resolutions (e.g., 150 ppi) might be acceptable for larger prints viewed from a distance.

  • Resolution for Web: For web display, a resolution of 72 ppi or 96 ppi is usually sufficient, as screens typically don't display higher resolutions effectively.

  • Image Size vs. File Size: Changing the print size only changes the resolution information associated with the image. It doesn't directly affect the file size or the number of pixels in the image unless you explicitly use the "Scale Image" function to resample the image.

Example:

Let's say you have an image that's 1500 x 1000 pixels.

  • At 300 ppi: The image will print at 5 x 3.33 inches (1500 pixels / 300 ppi = 5 inches, 1000 pixels / 300 ppi = 3.33 inches).
  • At 150 ppi: The image will print at 10 x 6.67 inches (1500 pixels / 150 ppi = 10 inches, 1000 pixels / 150 ppi = 6.67 inches).

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