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What is DPI?… and why we do not use it.
There is a lot of confusion around DPI or dots per inch. We are often asked about what DPI our photos are, and sometimes we are asked to retake photos to be 300dpi.
DPI does not equal quality or resolution in digital photos.
DPI refers to the physical dot density of an image when printed. It is used by printers to define the quality they need to print an image at a certain physical size.When you want to physically print a photo, for example on paper or fabric, you want to ensure that the image is large enough so that the printed image will look good. This is where DPI comes in. In the image below we fix the width of each image, and adjust the dpi – and you can see, especially in the lower dpi images, the difference in quality
A digitally stored image has no physical dimensions measured in inches or centimetres. Dots per inch makes no sense when the size of the image is not defined. The digitally stored image has a size in pixels. For example a photo might have 4000 pixels in its width and 5000 pixels in its height. We would describe it’s size as 4000×5000 pixels.
As a rough rule of thumb for fashion and product photos, if the longest size of a photo is 3000 px or more it is near full size and too large for a normal internet image, if it is between 1600 and 3000 px it is still quite large for an internet image but good if people are able to zoom in, between 800 to 1600 px it is normal for internet size. Less than 800 px it is getting too small for an internet image, the quality will be too low.
In the image below we show 3 images of a dress, the first is a large file, the second is larger internet sized and the third is lower internet quality. But they are still all usable, but with the smaller image the definition has decreased and when you zoom in you can see lack of detail starting to show.
We can lower the size (and quality) of a photo when requested, for example to suit a webshop where photos need to download quickly. We might, for example, be asked to supply 1200×1200 images. This will give much smaller file size, for example in the order of 500kB, instead of the full size files which could be in the order of 10MB. The quality will be lower, but still good enough for a webshop image and the smaller size will mean faster download times.
STOODIO do not normally increase the size of photos. You can use some photo editing packages to make larger images, but the program is adding pixels where they do not exist, and the quality of the photo does not improve with size and sometimes is worse.
For simplicity, we will make 1 dot equal 1 pixel (not always true, but OK for this example). If you want to print the image at 10 inches x 10 inches, and your printer says you need a minimum of 72DPI, you will need a minimum photo size of 720×720 px. You calculate this by multiplying the DPI by the length in inches, in other words at 72DPI each inch needs 72 pixels, and with 10 inches that is 720 pixels. If you need the same size of 10 inches x 10 inches at 300DPI, then you photo needs to be much larger at 3000×3000 px.
You can also think the other way around. If we supply an image 5000×5000 pixels, and your printer needs 72DPI, then you can print it a maximum size of 69,4 inches x 69,4 inches (176cmx176cm). You can calculate this by dividing pixels by DPI. If the printer needs 300DPI, then the size of the printed image changes to 16,7 inches x 16,7 inches (42x42cm).
As another rule of thumb, magazines typically use 150 DPI whereas newspapers will often use 72 DPI. This gives you an idea of the print quality.
To confuse things, often programs used for handling images will add arbitrary dpi numbers, mainly because they do not like to have no dpi associated with an image. So the same photo which has no physical size associated with it might be labelled as 300dpi or 72dpi, but as there is no physical size associated with it this is misleading. We sometimes have the same full size photo which is labelled as 72dpi in one program and 300dpi in another program.
If you need the highest quality photo, just use the full size PNG (or JPG) which we provide.
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STOODIO’s story – How we became us
STOODIO was born in the spring of 2016, when we realized that there was no company in the Finnish market that could supply the consistent product images and videos needed by e-commerce, which are needed to be delivered quickly, effortlessly, and at the same time cost-effectively.