Change image resolution – this is how it works

The resolution of images and photos is not always easy to understand for laypeople. We’ll show you what it is and how you can change it with graphics programs like Photoshop and the free GIMP.

Changing the image resolution is NOT necessarily the same as changing the image size (scaling) or changing the image format:

If you change the image size, the resolution usually stays the same. The image is either enlarged or reduced with a loss of quality.

If you change the image format, you save a JPG file as a PNG file, for example.

If you ONLY change the image resolution, the (digital) image quality / pixel dimensions will be retained – regardless of whether you reduce or increase it. Only the print dimensions change (more on this below).

For a better understanding, we explain what resolution is.

What is resolution (DPI)?

DPI stands for dots per inch and indicates the resolution of an image, i.e. how many dots of the image are printed on one inch:

  • The higher the DPI, the “finer” the image becomes, as more small dots are displayed per paper surface.
  • The lower the DPI, the “coarser” the image, as fewer dots are printed per area.

A resolution of 300 DPI for images has established itself as the standard quality for printing. In the field of image processing, one speaks of PPI (pixels per inch) instead of DPI – the principle is the same. However, the following must be considered here.

Change image resolution

If you have a digital image in Photoshop or GIMP, you can increase or decrease the image resolution in such a way that

  • the (digital) image quality is maintained. Consequence: Pixel dimensions and file size remain the same. Only the print dimensions change.
  • the image quality also deteriorates (scaling). Consequence: Pixel dimensions, print dimensions and file size change.

Example for the first variant with an image: 150 DPI, pixel dimensions: 591 x 591 pixels, print dimensions of 10 x 10 cm, file size: 1024 KB.

If you increase the image resolution from 150 DPI to 300 DPI, the print dimensions change to 5 x 5 cm (become smaller). The printed image will be smaller than before. That is logical, because now more pixels of the image are printed on one inch. You only “see” the change when the picture is printed or in the print preview.

If you reduce the image resolution from 150 to 75 DPI, the image dimensions are larger to 20 x 20 cm. The printed image will be larger than before because fewer dots per inch will be displayed. In the end, more inches are needed to display all the pixels in the image.

Example for the second variant with an image: 150 DPI, pixel dimensions: 591 x 591 pixels, print dimensions of 10 x 10 cm, file size: 1024 KB.

You double the resolution to 300 DPI. The pixel dimensions grow to 1182 x 1182 pixels, the image size quadruples to 4048 KB, the print dimensions remain the same.

You halve the resolution to 75 DPI. The pixel dimensions are reduced to 296 x 296 pixels, the image size is quartered to 256 KB, the printing dimensions remain the same.

Note: A maximum of 300 DPI is usually sufficient for private printing. For digital use, it should be at least 72 DPI.

Note: Sometimes you need to change image format to another (eg webp to jpg) online. MiConv File Converter will help you.

Change the resolution in Photoshop

So you can change the image resolution in Photoshop in both variants:

Open your picture and press the key combination Ctrl + Alt + i. The Image size window opens.

In addition to resolution, you can change this.

If the checkmark for Recalculate is missing, you can change the image resolution without any (digital) loss of quality (variant 1).

If the checkmark is set, you change the resolution with loss of quality (variant 2).

Finally click OK.

Change the resolution in the GIMP

GIMP uses two different dialogs to change the image resolution in the ways described above:

You can set variant 1 by clicking on Print size … under the Image menu.

Variant 2 can be found in the same menu Image under Scale Image. More here: GIMP change image size.