11.06.2016

DPI is an abbreviation for the phrase "Dots per inch" (the number of dots per inch). It indicates the resolution of the photo.

When it comes to parameters such as the matrix or image dimensions, the terms “pixels” or “dots” are indispensable. For professionals in the field of photography, the number of these very points determines the size of the image, which is called absolute. Photographers are accustomed to operate with such concepts every day.

But for many people who prefer to enjoy printed photos, the size in centimeters is very important (other measurements can be used). This size is considered to be relative.

To link the described quantities, they resort to such a parameter as "resolution", which is measured by the number of dots per inch. This value indicates how many dots vertically and horizontally can fit on one inch. When specifying only one value, the resolution is implied in both vertical and horizontal dimensions.

There are approximately 2 cm 54 mm in one inch. It means that DPI resolution shows, how many dots can fit in an area of ​​2.54:2.54.

Indication of resolution in centimeters (or in any other units of measurement) is relevant to mention in cases where relative size is mentioned. Sometimes professional photographers have to deal with customers who specify file sizes in pixels (for example, 3000:4000) in their orders, and then add DPI refinements (for example, 300).

Thus, such designations are used only by people who are not too versed in these concepts. But professionals are well aware that a file cannot have a resolution if its size is specified in pixels.

Resolution, measured in centimeters, for example, can only be spoken of when a printed image is meant.

With DPI you can answer a few questions:

1. What will be the resolution of the original file with a specific number of dots when it is printed?

2. How many pixels must be in order to obtain an image of the required resolution of a specific size at the output of the file?

3. What size will the image be if it is printed in a specific resolution with a certain number of horizontal and vertical dots in the source file?

Interesting publications on the site

"- What is the resolution of your photos? I need 300 dpi."

The phrase about "three hundred-de-pe-i"- a common misconception, sometimes acquiring the character of mass insanity. You have to hear this from people who have been working in the printing industry for years, and what is most funny - from professional photographers. The frequency of mention in the case and without makes you believe in mysticism. Funnier - only the legends of the 80s about the mercury antenna and army stories about balls under the foreskin. And if it is permissible for an amateur not to know all sorts of particulars, then a professional has no right to such delusions.

What is dpi, and why exactly 300?

DPI is an abbreviation of English. dots per inch(dots per inch) - Numerical expression of the bitmap resolution. Resolution determines how detailed your image will be when printed.

So here - there is no photo and there can be no DPI! If only because she does not have a denominator of a fraction, there are no these inches themselves. While the photo lives on your computer, viewed on the monitor, walks around e-mail, there is simply no need to talk about any dpi. The parameter becomes meaningful only at the time of printing. A photograph has only absolute resolution - the number of vertical and horizontal dots. Let's say if a photo was taken with a camera with a 6 megapixel sensor, then its absolute resolution will be 3000 x 2000 pixels. It's all!

Can this image be printed at 300 DPI? Yes, of course. How big will the print be? 25.4 cm * 16.9 cm.

If this happens in life, then I personally have never met. Either way, the dimensions and proportions of your magazine photo will be different. When printing the same photo with different sizes, the resolution will also be different, and in any case it will not be equal to 300 dpi. Not to mention that most often the layout designer crops the image in accordance with his ideas, terms of reference and the general concept. Let's repeat once again: while there is no printing, there is not and cannot be any DPI.

The dpi value only makes sense at the time of printing:

300dpi- This technical requirement to resolution illustrations in modern high-quality polygraphy. The typography lets you know that for your cover to print perfectly, you need exactly this resolution. Knowing the requirements for resolution when printing and the size of the print, you can already independently estimate how many dots vertically and horizontally the source image should have.

* - By the way, the number "300" itself is also very conditional here. Dispelling doubts is very simple - imagine a poster with dimensions of 1 x 1.5 meters. With a resolution of 300 dpi required by the unfortunate designer, the source file must have a resolution of 11800 x 17720 pixels, i.e. approximately 210 megapixels! Even the most modern professional photographic equipment has not even come close to such a value. And the posters both hung and hang.

For a black and white newspaper, for example, 50-70 dpi is enough, for a full-color offset in a book, about 120-150 is required, and for a billboard on the street - only 6-10. Everything here is determined by the features of the perception of the image by the observer - the larger the picture, the more distance a person can comfortably perceive it. The postage stamp is brought to the eyes, the magazine is held in the hands, and ten meters away from Bryullov's canvas. One thing remains unchanged - the angular limit of the resolution of the eye (about 1 arc minute). This is what professionals rely on when calculating the required resolution.

What permission is required in practice? In a general sense, the more the better. Unless we're dealing with outlandish destinations professional photography(aerial photography, photography of scientific processes, photo wallpaper), then in the vast majority of cases you can get by with an absolute resolution of 6-10 megapixels. Why is the misconception about "de-pe-i" so widespread? Because people don't really think about it.

Is everything simple? Oh sure. It took us three minutes to understand the essence. Therefore, if you hear from a designer (layout) the phrase "give me pictures with 300 dpi" - run away from him, you are dealing with dense laziness. And laziness, sooner or later, will ruin any business.

P.S.:
What does the value specified in the file properties (72, 150, 300 dpi) mean? This is only a recommended resolution when printing a photo in fully automatic mode, indicating a lazy owner to the printer. And this value can be painlessly changed to any integer positive number. Nothing will change in the photo itself.

P.P.S.:
Do you still require "300 dpi"? They say that psychology is best taught at a geisha school: "If you ask for a drink - don't be stubborn like a donkey - take a sip and put the glass on the table." Make it 300 dpi. Or just link to this article.

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What is dpi?

What is dpi? To begin with, it’s good to understand with what density of dots per inch (this is dpi) you need to print a picture. It is believed that the human eye cannot see more than 300 dpi, which is taken as the basis for the standard in printing (I would say far-fetched). It all depends on how far the print is viewed from, doesn't it? :-) If we consider the print High Quality and excellent detail, 10x15 cm in size - from a distance of 5 meters, then you still won’t see any small details on it! Therefore, the value of 150-200 dpi is not critical - for quality, which is quite sufficient. The quality is rather not a photo, but a viewing. And everyone will choose the distance for comfortable viewing of prints for their own vision.

The following table lists the most common photo card formats and the number of pixels needed to print at 200 and 300 dpi. From it we see that even a 2-megapixel camera is enough to print a regular 10 x 15 cm image.

3:4 - formats with an aspect ratio of 3:4 are marked (usually used in compact cameras).

Why do you need dpi?

So what is dpi? Why is it in the table? Why is it needed at all? With the help of dpi and the number of pixels, you can quickly estimate the approximate size of each side of the photo for printing in centimeters. So that no one suffers, I deduced a simple formula:

where:
x is the desired size of one side of the print in centimeters;
r - side resolution in pixels;
d - 2.54 cm (inch);
dpi - any desired number of dpi, for example, 300 :-)

By the way, dpi can only be a positive integer.

Example: we have a resolution of the image width of 2598 pixels, and dpi=300.
Then 2598 * 2.54 / 300 = 21.99, getting 22 cm across the width of the print

Of course, neither in the table nor in the formula did I take into account the distance from which the photographs are viewed (especially in connection with individual characteristics vision), so the dpi numbers are indicated as "professional" as possible. It is generally accepted that to view a print from a distance of about 30 centimeters (view anything, say, a 10x15 photograph), you need a resolution of 300 dpi. But all large pictures will be viewed from a greater distance ... no one wants to look at a print of 30x45 cm from a distance of, say, 10 centimeters ... If you don't believe, be sure to try it :-) you can advise printing workers who require an indispensable value of 300 dpi .

Trying to do it yourself graphics editor? Let me give you an example of Photoshop. Upload a photo, use the "crop" tool to make the desired aspect ratio (35 by 45), click "Image" at the top, then "image size", and there you will find points, millimeters, and dpi. Set the desired values ​​and click OK.

A couple of questions.
Does image resolution depend on dpi?
The answer is no.

There is a common opinion: the more points in the photo, the better it is.
Does the quality of a photo depend on the number of notorious pixels?
The answer is no.

The resolution of images depends on the number of pixels in width and height, and the resolution quality depends on the size of the matrix, good lens and skillful hands photographer.

Crazy hands are the deciding factor in most marriages. For example, even a resolution of 100 megapixels will not help a blurry photo, because it will still remain blurry - at any print size, any dpi and viewing distance. And then all the troubles are usually blamed on a bad camera or lens :-)

For full color offset printing 150 dpi is enough for books. Multi-meter posters may have even lower dpi. In general, dpi is only a reference value, or a command to the printer in automatic mode, which only tells about the desired scale when printing. And from what distance to consider a tiny postage stamp or an advertising poster on the street, a person will decide for himself. It's best not to see ads at all... :-)

But in specific shooting, dpi can be very important. For example, aerial photography for cartography. For a large map must be viewed very closely and carefully, especially by spies. Especially for spies with a camera :-)

Preparing for Photo Printing

Where is it better to print photos: at home on a printer, or at a photo printing kiosk? Home photo printing has the advantage of convenience and full control over the process. Disadvantages - the high cost of prints in comparison with a photolab. But in photography, it's the other way around. Therefore, many people look at photos on the monitor :-)

For hobbyists who still like to print photos, we will look at some typical cases.

Photos from digital cameras may have an aspect ratio of both 4:3 and 3:2 - depending on the camera model. Therefore, choose the appropriate paper size from the table above, and even better, find out in advance in the photo lab about what is available.

In cases where the aspect ratio of the image and the selected print format do NOT match, we crop the image in the photo editor in the desired ratio, or ask the photo lab to "print with margins". If they match, you should ask the photo lab to "make borderless", which will avoid narrow white stripes along the edges of the photo paper.

A small part of the image may be cropped, regardless of the cropping accuracy. This sad fact is connected with the tolerances of printing machines for paper play. Therefore, it is recommended to place significant image fragments further than 2 mm from the edge. Even better, to compensate for paper backlash, prepare images with a margin in width and height, but no more than 50 pixels per image side.

P.S. I have only given approximate reference values. And specific tolerances should be clarified with the workers of a particular photo printing.

What paper is better to print on: matte or glossy? On the glossy picture looks brighter, but great glare. On matte photo paper, the opposite is true. But no matter what you print, a bad picture will still remain bad :-)

Relevance: 2016

At least three parameters are used to measure the size of photographs - resolution digital image(in pixels), print size (in centimeters), and print resolution (dpi - dots per inch). A user who first encountered the task of converting an image, preparing it for printing is sometimes difficult to figure out these settings, has to act at random and go to the desired result through trial and error, wasting a lot of time and paper.

Let's take a simple example of a problem. You need to take a photo for ID. You can go two ways - go to a photo studio and take a picture there, paying 150 rubles for 4 small photographs printed on a sheet of 10 * 15 cm. The second option is to take a picture at home, prepare an A4 sheet for printing, on which to squeeze as many of your photos different sizes enough for several years to come. Then you go to a photo studio and print your creation on an A4 sheet for 30 rubles. It seems that the profit from one order is ridiculous, but if you need to print photos for several people at once (for example, when the whole family is photographed for a visa before traveling to another country), then you can save more money. And this is just one of the examples. Another question is how to keep the dimensions of the photos so that they are exactly 4 * 5 cm on the print (or some other size). In order to adjust the print size to the required one, you need to understand the connection centimeters, pixels and dpi.

Pixels

A pixel is a single dot that makes up an image. A pixel is also called a cell of an image on a monitor or LCD TV. Look closely at the monitor and you will see a barely noticeable grid, one cell of this grid is a pixel. The photo that you downloaded from the camera has a resolution of several megapixels, that is, for example, 6000 pixels wide and 4000 pixels high - this is 6.000 * 4.000 = 24.000.000 pixels or 24 megapixels. When viewed on a monitor, the picture is automatically scaled to the resolution of the monitor (about 2 megapixels). If we try to zoom in (stretch the photo), then to some extent the picture is stretched without a visible loss of quality, but then characteristic squares appear on it. This happens when the real resolution of the photo is less than what we want to see - the pixel size in the photo has become over size pixels on the monitor.

centimeters

What is "centimeter", I think, it is not necessary to explain. In our case, the size of the prints of a photograph is measured in centimeters. Usually photos are printed in the size of 10*15 cm, but sometimes larger formats are used - 20*30 cm (approximately corresponds to the A4 format), 30*45 cm (A3) and more. You have probably encountered a problem - you found on some site beautiful photo and decided to print it in a large format (for example, 20 * 30 cm), but after printing, they noticed that the quality of the print was not very good - the objects' outlines turned out to be a little blurry. The saddest thing is that this photo cannot be corrected by any processing. And all because the resolution of the photo on the site is, for example, 900 * 600 pixels. That is, for 1 pixel on the printout it will have a size of approximately 0.33 millimeters - while it is difficult to count on "ringing" sharpness! And here another image quality parameter appears, with which you can evaluate the quality of the print - DPI

DPI

DPI is an abbreviation for the English phrase Dots per Inch, which translates into Russian as dots per inch. This value just shows how many image pixels fall on one "linear" inch when printed (an inch is 2.54 cm). There is also the value of DPC (dots per centimeter), but it is used less often - whatever one may say, all these printing technologies came to us from where inches, feet, pounds, etc. are in use. So, let's return to our example - a picture of 900 * 600 pixels, which we decided to print in a format of 30 * 20 cm. Let's translate centimeters into inches for convenience - we get 11.8 * 8.9 ". If we divide 900 pixels by 11.8", then we get the print resolution 76dpi. This roughly corresponds to the resolution of the monitor with its "large" pixels, so the picture on the screen looks good. But to get a print of acceptable quality, you need a print resolution of at least 150 DPI, and if you want very good detail, at least 300 DPI. To ensure this resolution when printing 30*20 centimeters, the original digital image must have a resolution of 3540 * 2670 pixels - about 9 megapixels. So they found the reason why the photos printed "from the Internet" look blurry and cloudy. Now let's get back to our question - how to adjust the image resolution so that it prints at a given size? As an example, consider the preparation of photographs for documents.

Creating your own photo for documents - step by step instructions

Suppose you need to take some 4*6 cm photos and place them on a 20*30 cm sheet. How to do it?

1. Take the original image, open it in Photoshop. Select the menu item "image" - "image size". We are presented with the following dialog box:

In the dialog that opens, we see two groups of settings - "dimension" and "print size". The "dimension" group displays the dimensions of the digital image in pixels. We do not touch these settings! In the "print size" group, set the size we need in centimeters (the units of measurement are selected from the drop-down lists). In our case, this is 4 * 6 cm. We also set the print resolution to 300 pixels per inch, this will ensure good print quality.

By changing the print size settings, we see that the pixel dimensions also change. That's how it should be! After all this, press the OK button. The image changes in size. Now we need to copy it - use the key combination:

1. Ctrl + A (eng) - select all
2. Ctrl + C (eng) - copy to clipboard

What is copied to the clipboard, we will transfer to a separate canvas, see step 2. 2. Now we need to create a new image that will fit the 20*30 cm sheet that we are going to print to the photo lab. Select the menu "File", "Create", a dialog box appears:

Specify the size of the photo paper on which printing will be performed (20 by 30 cm) and set the resolution in pixels per inch to be the same as our photo has - 300 DPI. We press OK.

3. An empty image with a transparent background appeared. Press the key combination Ctrl + V and paste our first image on a new canvas. It will look something like this:

The image is pasted as a new layer. Move it to the upper left corner, then select the menu "Layer", "Duplicate Layer".

Another similar picture will appear on the canvas, initially it "lies" on the original layer. We move it and put it next to it. In the same way, we create as many duplicate layers as we need. After that, we perform the flattening of the layers (menu "Layer", "Perform flattening").

We save the picture in JPEG format, copy it to a USB flash drive and go to the photo lab. We tell the operator the following - "print this image with a format of 20 * 30 cm with a resolution of 300 DPI without scaling". At the same time, small pictures will have exactly the size that we indicated for them - in our case 4 * 6 centimeters. It is advisable to have a ruler with you to check the size of the prints.

The abbreviation is known to designers, computer scientists, those who have ever worked with an image. Gamers have also heard about this term with their cool special mice. Now we will try to deal with this abbreviation.

Options

If you ask the Internet about DPI, what it is and where it is used, you will get several answers at once. After all, there are three transcripts of this abbreviation:

• Deep Packet Inspection is a provider tool that collects statistics, checks network packet filters and their contents.
• Discounted Profitability Index is economic term, which is responsible for the indicator of return on investment.
• Dots per inch - translated from English as "dots per inch".

It is the latter option that we will consider.

Permission

Speaking specifically about DPI, it becomes clear that it means only a unit of measurement. But what? It turns out that this abbreviation is used to find out the resolution of an image.

Resolution itself is an indicator that indicates the number of dots (pixels) per unit area. Most often, this indicator is applicable to images of a digital type, but it is used when working with the granulation of photographic film, photographic paper, etc.

So, if you need to save data in a graphic file with the desired scale and print it all, then most likely DPI will come to the rescue. This value will indicate the number of dots per inch. If you have a resolution of 300 dpi, respectively, it equals 300 dpi.

Example

Another example to understand how this value works. Let's say your image has a resolution of 350 dpi. You need to transfer it to 10 cm x 10 cm paper. In inches, you get 3.9 x 3.9 inches. To understand what size the original image needs, you need to multiply 3.9 by 300. This will give us 1170 x 1170 pixels. With this indicator, the picture quality will be acceptable.

Application

Now more about where and how DPI is applied. What is it, we have already figured out. The value is used to indicate the resolution. We need the latter when outputting graphic data to a flat media.

You can also find this value in the specifications for the printer. May be 600 by 450 dpi. So it becomes clear that the devices are endowed with a resolution that is 600 dots horizontally and 450 dots vertically. In this case, we take a square of 1 by 1 inch for the area.

If we talk about the printer, then often this indicator is compared with PPI. These two values ​​mean the same thing. Use when you need to mix inks for printing. Then 1 dpi will be equal to 1 ppi. If the device does not need to mix ink, then this formula will look different. The index N is used, which indicates the number of colors used for printing. Then dpi will be equal to ppi multiplied by this amount, that is, by index N.

This calculation is the main advantage for inkjet printers. Unlike photo machines, string devices have greater value DPI at equal to PPI. Because more dots are exposed to transmit one pixel.

Other indicators

The DPI of an image is not the only resolution. As we have already learned, there is a relationship with other similar indicators. So, in printers, a halftone dot is represented by many small dots. They are called flash. The number of such flashes per inch is referred to as DPI. The number of dots that hide in this flash per inch is referred to as PPI. Accordingly, if the ratio of the two indicators is greater, then the image is better.

There is another indicator - this is LPI. The value indicates the number of lines per inch. This permission characterizes the work laser printer. The inch in this case is represented not by a dot, as before, but by a line. That is, to be more precise in the wording, then LPI is the number of lines per linear inch.

Another value is represented by the abbreviation SPI. It shows the number of elementary spots. The indicator is quite complex and not so often used in photo printing. But in general it is used for printing gradients. And if the PPI points to final result, then SPI is part of the process. Interestingly, in general, both indicators equal conditions have the same meaning.

Gaming mice

But it turns out that this is not all information about DPI. What is it, we in general terms understood. What is used for, also figured out. But they missed one thing. The fact is that the value is often found on packages with gaming mice. It is difficult to connect the information we received earlier with the parameters of the manipulator. But you can try.

The fact is that dpi in the controller stands for the same, but has a slightly different understanding. To be precise, for a mouse, this indicator is better deciphered as dots of cursor montion per inch. That is, the number of points of cursor movement per inch. Next to this value, cpi is used. It roughly means the same thing, and it would be logical to use this particular abbreviation. But in general, both one and the second value convey the number of steps that the manipulator passes per 1 inch.

And it should be understood that we are talking about the movement of the mouse, not the cursor. The movement in this case is interpreted as a step, and the step as a signal. If the dpi is high, then the device moves smoothly.

Marketing?

In theory, it turns out that this indicator, which is shouted about from advertising booklets and packages, is more of a marketing ploy. The fact is that few people know, but for this very speed, one should not forget about the port polling rate. It is known that on this moment the highest rate is 1000 Hz. You might think that if the mouse moves 2 inches in one second, then this figure will double. In fact, it turns out that it is still impossible to cross the threshold of 1000 Hz. So what is the advantage of this value in manipulators then?

DPI is an indicator that changes the speed at which the cursor moves on the display. And it does it most efficiently in the case of high-resolution screens. It is logical that if the display is large, then the mouse should travel a distance proportional to the diagonal of the monitor. Therefore, this value is important only for players and those who work with graphics. For them, an indicator of 1600 dpi is considered acceptable.

For other users who have a screen smaller than 1600x1200, 800 dpi will be enough. This value is the average for today. If the monitor is 1200x800, then a mouse with a resolution of 400-500 dpi will be enough.

findings

It becomes clear that DPI is a value that is more familiar to designers, those who work with graphics and printing. This is the resolution that allows you to determine the number of dots per inch when displaying an image on flat media. If we are talking about a mouse, then DPI in this case shows the movement of the mouse per inch.

If you have then the question of how to adjust DPI should not arise, since usually there is a special button on the case to adjust the resolution. In some cases, you can also configure through software. If you have a regular mouse, but you want to adjust its speed, then it will be enough to go to the settings on the PC and set the slider to the desired level.