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For some reason the website deleted my earlier post. Here it is again.
does the dpi of an image matter?
Does the actually in-camera dpi setting matter? Very little.
Does the number of pixels per inch matter? A whole lot.
I’ll try to explain why.
A digitally stored image has no inherent physical dimensions, measured in inches or centimetres. Some (not all) digital file formats record a DPI value value, which is to be used when printing the image. This number lets the printer know the intended size of the image, or (in the case of scanned images) the size of the original scanned object. For example, an image may measure 1,000 × 1,000 pixels, a resolution of 1 megapixel. If it is labelled as 250 PPI, that is an instruction to the printer to print it at a size of 4 × 4 inches. Changing the PPI to 100 in an image editing program would tell the printer to print it at a size of 10 × 10 inches. However, changing the PPI value would not change the size of the image in pixels, which would still be 1,000 × 1,000.
You shouldn’t print everything at the highest resolution possible. Even a 42MP photo, something that can reliably be blown way up, only spits out a 26-inch x 17-inch print at 300dpi. This is why standard print resolutions rarely get that high. Billboards are usually printed at just 15dpi, and bus wraps around 72 or 100dpi. However, if you’re printing a family picture for putting on your desk, a handbill, tract, or business card, people will look at it more closely, so don’t dip below 300dpi. (I.e., don’t print a 4 x 6 inch picture with less than 1,200 x 1,800 pixels.)
On the other hand, if you’re exporting a picture for use on the web, you can usually get away with a lot less resolution, from 72 to 96 dpi, as most computer/phone screens physically don’t have more pixels per inch than that.
Is there a way to change the dpi of an image?
With what I have just said, it should be obvious that you will rarely (if ever) need to. If you need a picture printed used at a specific size, at a specific resolution, just use some multiplication to find out how many pixels you’ll need.
I hope this helps,
William