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How Image Resolution Affects Print Quality - Photoshop Tutorial

So how high of a resolution value do you need for professional quality printing? The generally accepted value is 300 pixels/inch. Printing an image at a resolution of 300 pixels/inch squeezes the pixels in close enough together to keep everything looking sharp. In fact, 300 is usually a bit more than you need. You can often get by with a resolution of 240 pixels/inch without noticing any loss of image quality. The professional standard, though, is 300 pixels/inch.

Let's consider these pictures from Reddit. I opened Irfan View, but it doesn't show me how many pixels/inch?

Autumn in Woodstock, Vermont.

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Birdbox in Norway (by Studio Livit)

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    There are many questions on this site about resolution. In short: An image can't be said to have a resolution before you choose a physical size for it. – Wolff Mar 6 '20 at 7:29
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DPI isn't a meaningful measurement of image size/resolution in this situation. DPI is a ratio between the number of dots (pixels) in the image and the number of inches those pixels are spread out over. You can know the number of dots, but the "per inch" part doesn't occur until the image is printed. A 1000 pixel image printed at 1 inch is a 1000 dpi image; same image printed at 10 inches is a 100 dpi image.

Some image file formats carry DPI information that suggests a printing size for the image. If our example 1000 pixel image claims to be 100 dpi, then many programs will size the image to 10 inches (1000 dots / 100 dpi = 10" ) when you import the image.

When the image format doesn't allow for preserving DPI info, the application might use a default of 72 dpi (common on Macs) or 96 (common on Windows PCs, though sometimes it's 120 or other values). Or the application might use some other way of sizing the image.

In any case, you can see what Irfanview thinks by pressing I. That'll show you lots if info about the image, including DPI (which you can change if you like) and the size that the image will print IF using a print setting that sizes the image based on image pixes/dpi.

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Simply put one and play with the values:

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Menu>Information>Resolution>Change>Ok

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The reason you can't see anything in the DPI setting is because it hasn't been set yet, or is rather at the default screen resolution (72ppi for Mac, or 96ppi for Windows). The way IrfanView indicates a default resolution is to show the DPI fields as empty.

All you need to do is type in a value and press Change.

The physical print size will then be updated to reflect the DPI setting.

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