Scanner resolution details - role and impact (a)

Third, the role and impact of scanner resolution

1. The relationship between resolution and pixels

Pixels are the smallest unit for measuring image data. The secret of all digital images is to use these discrete, discrete elements to simulate continuous tones. Each pixel has four basic characteristics: size, hue, color depth, and position. By understanding these four characteristics, you can better grasp the resolution from different perspectives.

Let's talk about the size of pixels. The resolution is represented by the number of pixels per inch in the digital image, which means that all pixels in the same image are the same size. When scanning an image, the size of the pixel is determined by the resolution used. For example, a 600 dpi scanning resolution means that each pixel is only six hundredths of an inch. The higher the input resolution, the smaller the pixels, which means that each metric unit has more information and potential details, the hue looks more continuous; the lower the resolution, the larger the pixels, each The smaller the details of the metrics unit, it looks a bit rough. The combination of pixel size and number in an image determines the total amount of information it contains. At any time later, the pixel size can be changed by simply changing the resolution. If it is used for output printing, then changing the resolution automatically changes the size of the printed crystal.

The original grayscale or color photographs all have a continuous hue, that is, a smooth transition between adjacent colors or shadows, but the computer cannot understand any continuous thing, and the information is divided into individual units that can be processed. When the scanner assigns a color or grayscale value to each pixel in the image, it gives a continuous tone feeling because the pixel is small and the color or tone of the adjacent pixel changes little. This is where the characteristics of the hue that the pixel has play a role. Scanned images from scanners with a low noise figure and a wide dynamic range present a very natural continuous tone because they include a particularly wide tonal range from light to dark.

Let's talk about the relationship between pixels and color depth. The scanner assigns a color or grayscale value to each pixel in the image. A single pixel can only give it a value, but the scanner's color depth implies a fairly large number of colors or tonal ranges can be used as Its assignment, such as an 8-bit grayscale scanner can use 256 colors to assign values ​​to pixels in a grayscale image; a 24-bit color depth scanner can use 16.77 million colors to assign values ​​to pixels in a color image, and a 36-bit scanner You can assign a value of 68.7 billion colors to the pixels of a color image. Because pixels have such a rich range of color performance, images scanned by scanners with a high color depth can be vividly reproduced.

About the location of the pixel. If you look at a digital image a lot of times, an image is just a grid that contains many individual pixels. Each pixel has a definable horizontal and vertical position inside the grid. In most image editing programs, the coordinates of any pixel can be obtained simply by moving a tool called a "dropper" in the image. The physical size of the grid is determined by the total number of pixels and the resolution, which in turn determines the relative position of each pixel.

2. Resolution and file size and image size

The file size is the number of pixels in pixels, in kilobytes (1CB), megabytes (MB), or gigabytes (GB). The file size is proportional to the pixel size of the image. With a given print size, more pixels produce more detail, but more disk space is required for storage, and editing and printing can be slower. This means that the files have been expanded and the corresponding download, copy, and print times have increased.

The maximum image file size supported by Photoshop is 2GB and the maximum image size is 3000030000 pixels. This limitation limits the possible print size and resolution of the image. For example, the output resolution of a 100-inch X100-inch image can only reach a maximum of 300 dpi (30000 pixels/100 inches: 300 dpi. Most scanner drivers can be based on the editing method when the original image is previewed and the selected color method and input resolution Rate, automatically calculate the file size.

An increase in resolution will result in a sharp increase in image files, with a doubling of the resolution and a fourfold increase in file size. For example, scanning a 3 inch X 3 inch original at a scanning resolution of 600 dpi has a file size of 9.49 MB; scanning at a scanning resolution of 1200 dpi, the file size is 37.97 MB. If you want to scan an A4 color image, scan it with 1200dpi and the file size is about 408MB. It can be seen that the length of such a file not only occupies a large amount of hard disk space, but also requires a long working time. The actual experience will understand that this is uneconomical. Therefore, under the premise of maintaining good image quality, try to select the lowest resolution and reduce the disk space occupied by the file.

Some people may ask, as you say, high-resolution and interpolation resolution is not useless? No, if you are dealing with continuous-tone images with a high-end color image system, higher resolution is very important. This is because higher resolution can significantly improve the sharpness and sharpness of pixels in an image. Interpolation resolution is useful when scanning black and white images or magnifying smaller originals. For black-and-white images, the resolution should be set to the resolution of the output device. For example, to output a black-and-white image with 1200 dpi printing, the 1200-dpi interpolation resolution can also produce smooth lines without jaggies.

Once the scan is complete, changing the resolution of the image will only change its physical size, unless the sample is resampled to increase or decrease the information in the image, otherwise the file length will not change. This is why the file length of the large-resolution low-resolution image is not larger than the file length of the high-resolution small image.

(to be continued)