Pixel, resolution

DPI indicates the resolution, which is the number of points per inch in length. DPI can be subdivided into horizontal resolution and vertical resolution. For example, if the horizontal resolution of a 1 inch * 1 inch image is 100 dpi and the vertical resolution is 50 DPI, it divides horizontally into 100 segments per inch, vertically into 50 segments per inch, just like a grid on a square meter. this figure has 100*50 = 5000 grids in total, with a total of 5000 pixels. since the horizontal resolution is not the same as the vertical resolution, each pixel is a tiny rectangle.

Therefore, pixels are actually a concept of area. Generally, the horizontal and vertical resolutions of images produced by computer/digital cameras are the same, and each pixel is a tiny square, so we can say that "DPI indicates the number of images in the length of each inch" is actually "the number of points in the length of each inch.

The area of each pixel is determined by the production process. The higher the process, the smaller the area of each pixel. Each square inch of the screen can accommodate more pixels, and the higher the DPI value, the finer the image, the smaller the pixel to the point that the human eye cannot tell, and the image looks different from the actual one.

This is the concept of "how many thousands of pixels" for a digital camera. For example, a camera can take up to 1600 pixels * 1200 pixels of photos, the pixel value is 1600*1200 = 1.92 million, which is about 2 million. This is a 2 million pixel digital camera.

As a result, the 300 dpi mentioned in the question indicates that there are 300 points in length on the screen in both the horizontal and vertical directions. the actual height of the screen must be calculated by combining the number of pixels with DPI. for this machine, 400 pixels are 400/300 = 1.33 inch, and 533 pixels are 533/300 = 1.78 inch.

For a computer photo, you can change the resolution of the image in Photoshop's "image"> "image size" menu. The default value is 72, and the image is reduced, if you increase the resolution, you can zoom in or out the image (which causes loss of image quality). The real impact is the impact on the printing and output of images with high resolution requirements. You can open the "file"-"Print Options" menu to view the print preview.

Pixel: the smallest unit of components in a lattice image. pixels cannot be further divided into smaller units. In general, it is a square with color, light and dark, relative to the coordinates of the entire image and other information. A certain number of colors are arranged and combined with small square blocks, used to represent a dot matrix image, that is, a bitmap image. Images output by digital cameras, scanner scans, or bitmap software are bitmaps.

Resolution: pixels cannot be further divided into smaller points, but actually pixels are large and small. The number of small square blocks per unit area is the resolution of an image. Within a unit area, the more pixels are accommodated, the smaller the size of a single pixel, the higher the image quality. On the contrary, the smaller the number of pixels contained within the unit area, the larger the size of a single pixel, the lower the image quality. For convenience, the image resolution is not expressed by area, but by the number of bytes in the unit length on one side of the rectangle. The length is usually in inches, we often say that the resolution of a printed image is 300, that is, this image contains 1 inch pixels in 2.54 cm length (in combination with 300), and 90 thousand pixels in one square inch. Such an image is used for display on a 72-inch screen. at a ratio of 100%, the image size is about 16 times the size of the printing.

Note;

In fact, the resolution (DPI) of a product is fixed, that is, the area of each pixel is determined. The number of pixels is large, and the area of images that can be normally displayed is large. The number of pixels is small and the area is small, it is not clear to enlarge the image.