Length unit in Computer

<Reprinted please indicate the source: flyoxs-length unit in the computer>

 

Introduction: starting with several questions

 

Question 1: Why does the Photoshop ruler look like it is not the actual length on the screen?

Question 2: the words in the word are larger on the desktop, but small on the notebook, and eye pain. But when printing, No matter what printer is used, the final size is consistent, why?

Question 3: What does font 5 mean? How long is the metric unit?

 

After reading this article, you can easily answer the above questions.

 

1. Length units in real life

 

Let's start with the unit of length in real life.

We are familiar with the following length units:

• International Metric Units: meters (M), centimeters (CM), millimeters (mm), etc.
• English countries: feet (feet), inch (inch), yard (yard), etc.
• Traditional units in China: Li, Zhang, ruler, and inch

Note that International Metric Units are generally used in the world, while English units are only used in English-speaking countries. Chinese traditional units are only used in limited fields, such as the clothing industry, currently, young people do not know how long it is.

 

Their unit conversion relationships are as follows:

• 1 inch = 2.54
• 1 m = 3 Chi (ruler)

Ii. Display and pixel

 

In a computer, how does one express the unit of length? Of course, it is expressed in 01 strings.

In fact, the topic of this article should be "length units in computer graphics output devices ". There are two commonly used computer output devices: displays and printers.

Now, we will introduce our new guest, called pixel (PX ).

Pixels are the most commonly used units of measurement for display (TV), whether it is the former CRT or the current LCD. How long is a pixel equal? No one can answer because 1 px has different lengths on different monitors. A pixel is a physical light point, which emits light of different colors. Our monitor is composed of these dense points. Of course, if you don't pay attention to it, you won't be able to see it with the naked eye. You can use a magnifier.

 

One monitor has three important parameters:

• Size: we often say how many inches. This inch refers to the length of the display visible area from the upper left corner to the lower right corner (diagonal ).
• Physical resolution: w x H, that is, in the horizontal direction, W pixels in a row, H pixels in a column in the vertical direction, so the total number of pixels of the display is the product of them.
• Point distance: the distance between two adjacent pixels on the screen. You can obtain the distance between the two parameters above. The manufacturer specifies the parameters of the general display.

For example, the current display I use is the Great Wall m228, the size is 22-inch, the resolution is 1680x1050, And the dot distance is 0.282mm.

Here, by the way, we clarify a problem that is often misunderstood. On a display of the same size, is the physical resolution of the screen better, or is the smaller the screen, the better? Obviously, the bigger the page, the better, because there are more luminous points (more LCD lattice, we make a lot of money), and the field of view that can be displayed is naturally wide. However, when the resolution is high, the point distance becomes smaller because the unit length contains more pixel points. Another question: is the bigger the distance, the better, or the smaller the distance, the better? This allows the benevolent and wise to see wisdom. Young people like to have a little dot and a little dot, so the picture looks clear (the quality of the fact film itself has not changed, but the image is reduced when it is displayed, and it looks much more refined ). People who are older can't stand the monitor with a small distance, because when operating the computer, all the fonts are small and it looks hard.

 

3. printer and font size

 

In the printing industry, there is no such saying as pixels. People say more about dots and DPI. In fact, the pixels here are the same as those in the monitor, indicating the resolution of the image/graphic output device.

DPI is the abbreviation of dot per inch, indicating the number of points or number of lines that can be printed per inch, used to indicate the printer's printing resolution. This is one of the main parameters to measure printer printing accuracy. In general, the larger the DPI value, the higher the printer printing accuracy. DPI and the dot distance of the monitor indicate the same physical meaning. At present, the cheap black and white printers on the market are generally 300 dpi, that is, the White Paper is 1 inch (2.54 cm) such a long blank space, the printer can control 300 points, that is, each point can be printed without printing.

How do people describe the size of printed text if printed? This is the font size below.

There are many font size units. You can use pixels (points) to describe them, but it is too hard to use them. In fact, the most common unit of a font size is point, which is abbreviated as PT. Speaking of LBS, I think everyone should be familiar with it. When you open the word software, the most common choice for font size selection is "Small 4". In fact, small 4 is 12 lbs. In the drop-down list of the font size, you can directly use Pt as the unit.

You may have noticed that there are two types of font size units in Microsoft's word, for example, "first", and "second", and directly use Arabic numbers, the Unit is lbs. Due to traditional reasons, in China's printing industry, there are two types of fonts:

• Number System: it is a system consisting of several living words that are not multiples of each other. In word, such as "Xiaochu" and "4th.
• Point System: it is also called the pound system. It is a transliteration or transliteration of an English point. In word, such as 36 (PT) and 14 (PT.

So how big is number 1 in the number system? What about 1pt in the point system? In fact, these two problems have little significance, because the initial manual printing is based on a set of common fonts (movable words), and the number and number are only relative units. History is a thing of the past. We don't need to recall much, just like the QWERTY keyboard, to increase the burden on beginners without reason. We only need to know that 72 PT is about 1 inch or more precise, 72 Pt = 0.996264 inches.

For the font size of the number system, see the following table. Note that the font size in the printing industry is slightly different from that in Microsoft Office Word. The following shows the effect of comparing the font size and the number of pounds used by word:

Initial number 44pt

Xiaochu 36pt

26pt 1

24pt

2nd 22pt

Xiao 'er 18pt

16pt 3

3rd 15pt

14pt 4

4th 12pt

10.5pt 5

5th 9pt

7.5pt 6

66.5pt

5.5pt 7

8th 5pt

 

 

 

Iv. Windows Screen DPI settings

 

Your mind may be on the rise, because until now, you have not been able to solve the problem 1 mentioned at the beginning of this article. After reading this section, you will have some gains.

In fact, no computer-aided design software can accurately draw lines on the screen that are expressed in units of actual (metric) length, unless it knows the details of the display you are using and related settings.

We can compare the printer to find out the problem. The length of lines specified in the document or how high the font is, the printer can accurately print the desired length. Why? Because the application software is driven by a printer, you can know the DPI of the printer (the number of pixels corresponding to 1 inch ). If the resolution of a printer is 600 dpi, it is easy for the application software to figure out a 1 cm point mark (1524 = 1/1524*2.54) for printing 600 ).

Back to the display, the printer has DPI, then the display, the display can be a variety of ah? Certainly, the system does not know, because the monitor does not define a general standard interface for the system to call, so the system does not know, nor can it know the DPI of the Monitor (or the point distance is more appropriate ). This is also an industry reason. The communication interface of the previous generation (between the PC and the display) is VGA, which can only transmit analog signals. In addition, the display was not integrated with MCU and Rom, therefore, you cannot save the display information.

In other words, because the monitor does not provide a driver, the system (PC) cannot know the DPI of the mounted display, and thus the line segment and text of the actual length unit cannot be correctly drawn on the screen.

Although the system does not know the actual DPI of the monitor, Windows assumes a DPI for it, but this assumption is usually incorrect, so what you see on the screen is different from the actual length drawn by the application software.

Next, let's analyze the DPI that Windows assumes for us.

Right-click the blank area on the desktop, select "properties", switch to the "Settings" tab, and click "advanced" in the lower right corner to bring up the Display Properties dialog box (under Windows XP), for example:

For example, in the DPI settings drop-down list in the display box, Windows sets 96 DPI for our display by default. Now let's verify that this value is correct.

As mentioned above, my monitor is a 22-inch 1680x1050 resolution with a point distance of 0.282mm, that is, the length of a point is 0.282mm. First convert it to the inch unit, and then divide it with 1 to get the DPI of my monitor:

DPI = 1/(1/0.282/25.4) = 90 (DPI)

It can be seen that there is a difference between the two, which is the reason for the inaccurate display effect. You just need to change the DPI settings to custom settings, then adjust to the correct DPI calculated by yourself (90), OK, restart the computer, and then measure the amount in Photoshop, is the display length accurate? Is the width of the A4 Vertical page (100% view) in word 21 cm? Is the text size on the page consistent with that on the printer?

In other words, changing the DPI of Windows display settings makes it completely consistent with our display, and does not seem to have any practical significance. However, with this knowledge, can you calculate the 10 cm scale drawn by the drawing software, and how long is it actually displayed on your screen? Verify it with a ruler.

(Calculation method prompt: actual length (CM) = software claim length (CM)/2.54 * DPI set in Windows * dot distance of your monitor)