The concept of image size and pixel in Photoshop

There are probably a lot of beginners who know that a piece of film if the pixel is too high, it will take up memory, the output will be very slow. But if the pixel is low, the slice will not be clear, we should be very clear to the situation and use of the computer to set the pixel, but how to set it?

The image on the monitor is made up of many dots called pixels, meaning "elements that make up the image." But to be clear: pixel as a size of the image, only exist in the computer, as RGB color mode only exist in the computer. Pixel is a virtual unit, in real life there is no pixel in this unit.

Here the small series using Photoshop to explain, open the picture and then click on the menu bar (image-image size), you can see the following right image information

We are already familiar with the pixel size above, which refers to the size of the image in the computer. The size of the document under it is actually the size of the print, which refers to the size of the image printed. You can see the print size is 17.64x10.58 cm. It can be printed on a A4 sized piece of paper.

Does that mean that 500 pixels equals 17.64 centimeters? So is the size of 1000 pixel print 17.64x2=35.28 centimeters? This view is wrong, the computer in the pixel and traditional length can not be directly converted, because one is virtual one is realistic, they need a bridge to be able to convert each other, this bridge is located in the document size width and height below the resolution. Note that the resolution here is the print resolution, and the "display resolution" is different.

Now look at it with a value of 72, followed by pixel/inch, which means "pixel per inch". Inch is the traditional length, then this "pixel per inch" in other words is "how many pixels per inch." Refers to how many pixels are printed in a 1-inch length. Now the value is 72, then the 1-inch paper is distributed 72 pixels, 2 inches is 144 pixels, and so on.

Why not "pixel per centimeter"? This is mainly the use of English units more extensive, we usually say the TV or monitor the number of inches is in. This is also true in the publishing industry, so in order to facilitate calculation and conversion, "pixel per inch" is usually used as the standard for printing resolution. Referred to as Dpi,dot (dots) per () Inch (inch).

In Photoshop, you can also change the resolution units to conform to our custom "pixel per centimeter", the following left figure. Think about it, what is the pixel size if we adjust the print size and print resolution to the image shown in the bottom right?

First look at the resolution: 80 pixels per centimeter. Then look at the width is 10 centimeters, so the width of the pixel is 80x10=800 pixels. Then the height is 480 pixels.

Under the premise that the total pixel is unchanged, reducing the printing resolution will enlarge the printing area of the image. Increasing the print resolution reduces the print area of the image.

The above conversion process we all use cm and "pixel/centimeter", because this unit and our usual habit is closer. But keep in mind that in international standards, the Print resolution unit is "pixel/inch".

How to apply pixels:

1. Generally for the printing resolution, the printing industry has a standard: 300dpi. is to print the image resolution, at least 300dpi can be, below the value of the printed image is not clear enough.

2. If the printing or inkjet, only need to 72dpi. Note here that the print is not printed. Printing refers to the use of ordinary home or office inkjet printers. Inkjet is the streets of large-area advertising, because the demand for a small number of generally not for printing.

The print resolution and print size, as the name suggests, are useful in those applications that require printing or printing. such as poster design, newspaper ads.

3. For Web page design, and so on mainly on the screen for use, you do not have to ignore the print resolution and print size. You just need to define the image size by pixel.

It is important to understand that the two main image input devices, digital cameras and scanners, produce images that are measured in pixels. So if you have to say that without scaling the image, how many pixels tall a person has. That can only see the digital camera or scanner input to the computer image size is how much. If you shoot with a 8 million megapixel camera, it's definitely bigger than the 2 million-pixel image.

Now let's be clear about the two dimensions of the image and the conversion relationship:

1. One is pixel size, also known as display size or display size. The pixel value equivalent to the image.

2. One is the printing size, also known as the printing size. You need to refer to both pixel dimensions and print resolution to determine.

3. Pixel size (pixel/inch and inch) is the same as the resolution and the length of the printed dimensions, and the size of pixels = print dimensions.

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