Resolution problem in image processing

The relationship between the resolution and the size of the output of the laser imagesetter If the output device of the image is a laser image-setter or a plate-making machine, rather than a continuous modulation output format, as long as you know how to screen, you can determine the amount of data, The most commonly used screening method is AM screening. It uses different points of the same size to indicate the change in shades of color. The big idea is deep-tuned, and the little idea is shallow. In this screening mode, if the output resolution is appropriate, it can exhibit a wide range of gradation, and can also show a wealth of details. When the output size is set, the output resolution is the product of the screening coefficient and a coefficient, which becomes the screening factor, usually 2 or 1.5. For normal prints, multiplying by 1.5 is enough. For prints with screens higher than 150 lpi and printed on glossy paper, multiply by 2.0.

If the original has not yet been scanned, consider the relationship between output resolution and size so that the scanned image will contain the correct information. The only thing we have to do is set the scan resolution. For example, a “4 X 5” transmissive document that wants to be output in 150 lines, 36 inches in width—enlarged 9 times, with a scanning resolution of 2025 ppi (near the scanner's maximum input resolution) Contains enough data, you can output the size of your design. If the original is already in the form of a digital file, it can only be output in the corresponding size and resolution, and no more flexible arbitrary changes can be made. If you want to increase the size and increase the resolution, you need to re-sampling the image.

Formula 2: Scan Resolution = Magnification X Screen Number X 1.5
Line resolution resolution and size Scanning binary images - the scanning resolution of the lines is rather special. To avoid "sawtooth edges", the resolution of linework is always equal to the resolution of the device, up to 1200ppi. If the output device is a 600 dpi laser printer, the image resolution is 600 dpi. If the output device is a 2540dpi laser imagesetter, the linework has a resolution of 1,200 ppi. Some output centers prefer higher output resolutions, so listen to their opinions.

The size and resolution relationship of FM screening Another method of screening is FM screening, also called random screening. Now FM screening is mainly used in the high-end prepress market, so that high-resolution laser imagesetters and coated papers can better reflect the details that can be displayed by FM screening. There are also different views on the resolution of FM screening. Some experts believe that the effect of AM screening can be achieved with lower resolution, but others believe that high resolution can show the subtleties of the image. When selecting the output center, you must choose to have successful FM screening experience and respect their suggestions.

Safely Enlarged Image Whether or not the information contained in the image is sufficient to output as designed, as long as the data is sufficient, you only need to adjust the size resolution of the graphic text without changing the size of the file. If the data is not enough, you have to re-acquire information, increase the size, increase the resolution, or both. There is also a third case: if the picture is larger than what is needed and the resolution is higher than what is needed, it should be compressed to remove extra digital information. If you do not remove it, you can only increase output time and cost without increasing quality.

Simple scaling Most image editing software has a dialog similar to Adobe Photoshop for setting the image size. To scale the image without changing the file size, first check that the aspect ratio and file size are locked, and then change the image size and resolution. When the file size is constant, increasing the image size will automatically reduce the resolution; if you increase the image resolution, its size will become smaller.

Resampling If the image file contains too little data to output at the resolution required by the device, you will need to increase the size of the image while increasing the size of the file, or increase the resolution, or all three. This process is interpolation, increasing the number of pixels without adding more new details (the file size should not be locked when you change the image size and resolution). Most image editing software and many wide-format output devices integrate different effects of interpolation programs. There are some programs that do very well. After the image is magnified, the image is still very clear and no change in sharpness can be seen. Some software will make the image appear fuzzy and blunt. When you do not know which software to choose, you can use different software to process the same file (such as software provided with Adobe Photoshop and wide-format output devices), and then use a magnifying glass to compare their differences.

If the user is not an expert in this area, they put the resampling process to the device. When re-sampling is important, try to put this process last. We prefer to get low-resolution but clear images from our customers, rather than interpolating sampled blurred images.

There are several interpolation methods even in the same interpolation software. For example, Photoshop provides three calculation methods: binary three times, bilinear, and nearest point methods. Which one do you choose? This depends on the characteristics of the image and magnification. In general, binary cubic interpolation gives a clear, high-quality image. Bilinear interpolation is used for large magnification or unwanted details or smearing in the image. Binary cubic interpolation for such images tends to give unsatisfying and blunt results.

Increasing image size with resolution-independent applications In most programs, magnifying an image increases the geometric relationship between the image file and the required memory. By doubling the resolution of an image without changing the size of the image, the file is more than doubled but quadrupled. The most commonly used image editing software, Adobe Photoshop, often occupies 3-5 times the memory of an image when doing some real-time processing. Sharpening, enhancing, or special effects on 40MB, 80MB or larger files is simply a test of your computer and your financial capabilities.

Especially when working with large files, it is best to use Live Picture or cross-platform Macromedia Xres software. Both programs store data in their own unique, object-oriented, and resolution-independent formats. Prior to exporting, using these software, real-time monitoring can be achieved and any step of the operation can be changed prior to rendering. However, this method also has limitations because it starts with our design as a method of basic scanning, or as a method of painting a hand entirely.

Enlarge Image in Live Picture When importing a scanned file or other picture into the Live Picture software, two separate files are created. One is an IVUE format file that can be previewed and edited; the other is a FITS format file that can record each edit step in an unchangeable mathematical manner. This technique saves the original image and allows real-time monitoring. Compared with other programs, it only occupies little memory and the file size is very small. When the work is done, you can preview the output size. Live Picture allows users to change multiple targets. If we often retouch, splicate or perform other editing operations on the image, we will be very optimistic about Live Picture's powerful feathering, masking, and deformation capabilities. It can change the image while ensuring the image quality.

However, do not think that you can magnify a low-resolution, small-size illustration into an image as large as a billboard without sacrificing quality. Resolution Independence can only be entered in the original scan or pixel-based image file to form a FITS file for editing. Although Live Picture's interpolation algorithm is classic, if you want to magnify a scanned document and a pixel-based document more than two times, the quality of the image will be degraded. Therefore, unless you are using a drawing artwork in Live Picture, you will need to determine the relationship between the size of the image and the resolution when you first scan or create an image.

Magnify images with Macromedia Xres software Macromedia Xres can be used on both PC and Mac platforms, and they have independent resolution settings and magnification on both models. It offers two modes of operation, direct mode with images under 10MB and Xres mode with images over 20MB. Direct mode is used to directly process pixels, so it is very slow when dealing with large files; in Xres mode is the block processing of images, high speed, regardless of resolution, it is necessary to accelerate the image rendering . It should be clear that some creative features and masking features in the Xres model cannot be used. It is not flexible enough as a tool for the production and design of wide format prints.

Sharpening or Adjusting the Size If the document is not processed by the exporter but it is prepressed on its own, it is important to understand that sharpening or adjustment is an integral part of the prepress. Because the interpolation process softens the entire view, sharpening is especially important for magnified images. The larger the image sharpening, the larger the magnification and the deeper the sharpness.

For this reason, it is important to set the final size resolution before image sharpening (if you use interpolation to process the image, use sharpening) if you sharpen a small or low resolution image and then reacquire it Making it a high-resolution or large-size image looks too blurry. It is also not advisable to sharpen the same image several times at the same time. On the contrary, if the compression is performed after sharpening the image, the last small file is especially stiff.

Before the color correction and adjustment, the size and resolution of the final image are also considered. In a large-format image, a smaller color image will have a larger change; some colors such as deep yellow give people different feelings when it covers a large area. Therefore, once the image is magnified, the color of the manuscript should be reviewed.

To magnify an image successfully, learn as much as you can about output dimensions, output techniques, and output materials. In this way, no matter how you do it will not go wrong.