Image resolution setting in PHOTOSHOP software
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Image resolution refers to the number of points per unit length, reflecting the dimensional accuracy of the input pixels, expressed as the number of dots per inch of length. In digital images, the size of the resolution directly affects the quality of the image. Resolution is a very important issue in color image processing. How to produce high quality images at the existing device level is a factor that cannot be underestimated. When we face images in pixels, we first need to know that the images we process are digital.
To understand the resolution of the image resolution, we first need to know the computer image file first.
Computer images exist in the form of computer files, which are essentially just digital codes. The biggest difference between them and the so-called (traditional) images is that the images of the computer are data, not analog (digital images). It is the result of analog image data. It is a discrete sample of a general image, and thus has some concepts not found in conventional images (such as Pixel: on a computer, composed of more basic units, these basic units are called “Pixels.” Pixels are described point by point, with a clear position and color value. True color images each point with 24bit (RGB file) or 32bit (CMYK file) data to describe color. There is also the concept of resolution , as already mentioned above, it will not be repeated here).
In addition, when we describe the size of a traditional image, we just need to say the size. Such as 8 open, 16 open, etc., but when we describe the computer image, in addition to describing its size, we also care about the amount of its data, usually expressed in bytes. The number of bytes of a computer image file is related to the size, pixel value, resolution, etc. of this image.
The quality of an image is closely related to image resolution and size. For images of the same size, the higher the resolution, the sharper the image. The main factor determining the resolution is the number of pixels per unit size, so the number of pixels is also related to the resolution.
Whether it is a printed output image, a multimedia image or a web page image, the resolution and size of the image must be determined before production so that the image can be edited and processed more efficiently.
In the image processing software Photoshop, whether you change the image resolution, size, or increase or decrease the number of pixels, you need to use the Image Size dialog box (shown in Figure 1). The following can be set in the dialog:
Pixel Dimensions: Pixel values for displaying the width and height of an image.
Documet Size: Used to set the width, height, and resolution of the changed image.
Constrain Proportions: Select this check box to control the ratio of the width and height of the image, ie the height is also changed as the width is changed. When the check box is canceled, the height is independent of the width, ie changing the value of any item does not affect the other item.
Resample Image; when this check box is not selected, the image pixels are fixed, and the image resolution and size can be changed; when this check box is selected, the image resolution and size are changed, and the number of image pixels will vary. The change, at this time, in the re-image pixel list box, a selection method of the interpolation pixel, that is, an algorithm for inserting pixels in the image when the number of pixels is increased or decreased, is selected.
There is a close relationship between the resolution, size and number of pixels of an image. An image with the same resolution, if the size is different, its pixel number is different. The larger the size, the larger the file saved. Similarly, increasing the resolution of an image will also make the image file larger. Therefore, modifying the parameters of the first two directly determines the parameters of the third party. When the number of pixels is fixed and the image resolution changes, the image size must change accordingly. Similarly, when the image size changes, the resolution will automatically change in the opposite direction, and there is no sampling problem. Note: The image resolution affects the display size of the image on the screen. When the image's length and width are the same, the resolution is doubled, and the original image will be displayed on the screen twice as much as the actual image. In actual work, it is usually necessary to adjust the image size without changing the resolution, or to increase the size by increasing the size. In this case, the number of pixels will also change. When the size is increased and the resolution is increased, the number of pixels must be increased in the image, and then the image is resampled to increase or decrease the number of pixels in the image with minimal distortion.
Open the Image Size/Auto Resolution dialog box (shown in Figure 2). In the Screen text box, the user can set the dot frequency of the output device. In the Quality option group, you can set the quality of the printed matter: when set to Draft, the resolution generated is the same as the dot frequency (not less than 72 pixels per inch); when set to Good, the resulting The resolution is 1.5 times the dot frequency; when set to Best, the resulting resolution is 2 times the dot frequency. The photoshop software will automatically calculate the resolution required by the user and return to the Image Size dialog. The value of the new size and resolution has changed. The value currently displayed by the resolution is the number of nets entered by the user.
In digital images, the higher the resolution, the sharper the image, but the larger the file produced, the higher the memory and CPU processing time required for the job. So when making images, use different resolutions depending on your needs. Be aware that the resolution of the image used is not as high as possible, but consider the medium in which the image is ultimately released. If the resulting image is used for computer screen display (such as multimedia or web image), the image resolution only needs to meet the typical display resolution (72ppi or 96ppi). If the image is used for printouts, high resolution (150ppi and 300ppi) must be used, and low-resolution image printouts will have noticeable grain and jagged edges. For the setting of the line scan image resolution, it is not necessary to make the image resolution higher than the output resolution; for grayscale and color bitmap resolution settings, it should not exceed twice the output dot frequency (1.0-2.0 times).
Also, to get the best results when producing a smaller image, you can use a large original image and then scale the image onto the page, or use the USM Mask filter after changing the image size. If you want to change the image to a larger size and guarantee the quality of the image, it is best to rescan the image at a higher resolution. Image resolution changes are often involved in image processing. It is unwise to generally reduce the resolution of the image and then increase it again. This is the sampling that is usually mentioned, ie the increase and decrease of pixels. When the resolution is lowered, the pixels in the image are reduced by deletion; when the resolution is increased, the intermediate interpolation method is used to add information that is not in the original image. In a fractional image processing system, it is often tried to buffer the inconsistency between the two initial pixels and the added pixels, which results in a slightly blurred image.
In Photshop software, the Image Size command is different from the Canvas Size command. The image size command can only be used to change the image size without changing the image. However, the canvas size command will not only change the image size but also change the image.
How to set the appropriate image resolution and produce relatively high-quality images is a process of continuous accumulation of experience. Only when you are familiar with the requirements of users, familiar with existing equipment, and familiar with the requirements of the back-end printing process, can you master the mastery.