(With this, other changes are possible too, but are of no importance for this argumentation.) With Photoshop you can do this by means of Save for the Web. I wanted it to fit in the right column, so I resampled it with Irfanview to 178 pixels wide. The picture on the right side of this page was 1063 pixels wide. Other software for example mention 96 dpi or 120 dpi. Why does Photoshop indicate 72 dpi at Save for the Web? Simply because a box has to be filled in. Photoshop and Save for the Web (72 dpi? No) Now divide the pixels (in width or height) by inches (in width or height). Determine the size of your screen in one direction (width or height). To determine the dpi (px/inch) of a screen:Ĭalculate the screenresolution (width x height in pixels). The image itself has no dpi, but only pixels.Įxplanation: The image is reproduced 1 to 1 (pixel on pixel), that’s why it has the same dpi (ppi) as the screen on which it is shown on that particular moment. etc.īut only on the moment of presentation. On a screen of 96 dpi is the image 96 dpi etc. But on a screen of for instance 100 dpi is an image on that moment 100 dpi too. And as computerscreens formerly often had a resolution of 72 dpi, the misunderstanding arose that an image on a screen or on a website is always 72 dpi. Such an image hasn’t any dpi, only pixels. So on a screen of 72 dpi the presentation of that image is 72 dpi too. The dpi (px/inch) of the PRESENTATION of an image on the screen is identical to the dpi of that screen. But it is useless, your videosystem works with pixels only, not with centimeters or inches. Of course you can try to find out with a ruler how many centimeters or inches that very picture on that very moment measures on your screen. A photo on a screen has only a 'size' in pixels. It doesn’t matter how large your monitorscreen is measured in centimeters or inches. For example: a photo sized 512 pixels wide on a 1024 pixels-wide screen, covers half of that screen in width. Or actually just the reverse: every pixel of the image takes up the space of exactly one pixel of the screen. And when a picture on your screen is shown, then on each screenpixel is one picturepixel. Of course it is possible to calculate the dpi without Photoshop: pixels (height or width) divided by inches (heigth or width) is dpi.Īn image on internet or a monitorscreen is not 72 dpiĪ computerscreen (monitorscreen) is nowadays usually adjusted at 1024 x 768 pixels (this is called screenresolution). How to calculate the dpi without software It also works the other way around: change the printing-measure, the dpi-number of the picture will be shown. The moment resampling is off, you can change the dpi-number, the according printing-measure is given. But beware: you have to uncheck the resample-box! Resampling means calculating a new It doesn’t tell you anything, you can change it in any number you want, it doesn’t change anything of the picture. When you open a picture in Photoshop a dpi-number is mentioned. So watch out in which contexts DPI and RESOLUTION are used.ĭpi (actually ppi) is only important in case of printing. RESOLUTION is just like DPI a confusing term. The resolution of a print is expressed in Pixels per Inch The resolution of a photo is expressed in Pixels (w x h) Only then you can speak of pixels per inch (ppi, regrettably ususally called dpi). From the moment you are going to print there is the matter of size, given in inches or centimeters. Such a file only has a subdivision, a resolution, in pixels. A photofile in a camera or (stored at) a computer has no size in centimeters or inches. This is a number without any meaning, it is an invented number! A box (field) has to be filled in, so every producer simply invents a number. In that row also a value for dpi is given, f.e. These properties are called the EXIF-data. Do a rightclick on your file and next: Properties > Summary > Advanced. You can find the properties of your digital photos in a photo editing program, but also in the Windows Explorer. The dpi-value in the EXIF is meaningless. A better notation for PIXELS PER INCH would be: px/inch. But to make it even more confusing the term DPI is also used for PIXELS PER When it concerns the inking of prints, it means DOTS PER INCH. Unfortunately this is usually calledĭP I is a confusing conception. For all these bewildered people I have written this article. The end is usually an enormous confusion of tongues. Some people try to explain it, others meddle with this. Searching with Google with the terms forum 300 dpi results in a long string of questions: how is it done, I don't get it. 300 dpi, 72 dpi, EXIF and dpi, resolution, printing, 72dpi, 300dpi, dpiĪnd ppi, pixels, printerresolution, pixels per inch, dots per inch,Ĭamera and megapixels (MP), dpi/ppi and photoshop
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