In the prepress work, we often encounter the customer to ask some simple questions. In view of this, this paper uses the question and answer form to explain in detail some of the common problems related to image processing, and it is expected to help colleagues and enthusiasts.
1. Q: Should I use CMYK or RGB?
A: Many image processing software allow image files to be processed using either the CMYK or RGB image modes. However, the printing process of the printing factory uses CMYK, which uses four primary colors of inks: Cyan, Magenta, Yellow, and Black for magazines, books, cards, and advertisements. And other printed matter and various types of packaging products printing. RGB uses the three primary colors of color light, namely, red, green, and blue to represent the color and gradation of the image. If your file is in RGB format, it needs to be converted into CMYK format before printing. So when you start designing an image, you use the CMYK mode, because when the image is converted from RGB mode to CMYK mode, the color conversion is not always accurate, and some color information will be lost in the conversion process. The impact can be more profoundly appreciated from the transformation of solid patches.
2. Q: How large is the image resolution?
A: Generally speaking, the final output resolution of images used for printing should be no less than 300 dpi. If the resolution of the image is not so large or a small-size image is stretched to a larger size, then the printed image is printed. The image is jagged and blurred. Resolution and image size is not the same on this point can be explained by the following example: a size 3in x 3in, with a resolution of 300dpi image is stretched to 6in x 6in, you will see the image The resolution becomes 150 dpi. Although the image size becomes larger, its resolution is reduced. Once the resolution of the file is reduced, the lost resolution cannot be compensated.
3. Q: How large should my image size be?
A: For this issue, the most important thing is to figure out the size of the final printed image. If the size of the final printed image is 3in x 3in, then your image files at least 3in x 3in, a resolution of at least 300dpi; if you are not sure specifically how much the final print size, it will use when scanning at higher resolution Larger size scans. One principle to keep in mind: You can reduce the size of an image file, but you can't enlarge it with enough resolution.
4. Q: Is platform scanner better than roller scanner?
A: The scanning performance of the roller scanner is better than that of the platform scanner because its core components are different. The roller scanner uses a photomultiplier PMT, and the platform scanner uses an optocoupler CCD. For the average user, the price of the platform scanner is more acceptable, so the platform scanner is more cost-effective than the drum scanner in the case of less stringent quality requirements.
5. Q: Can I use images on the Internet as printed manuscripts?
A: The images on the Internet are generally GIF and JPEG files with a resolution of 72 dpi. Without affecting the visual effects of the screen, these files are all compressed in order to ensure fast transmission over the network. Therefore, many subtle information of the images are lost. Basically, high-quality images cannot be printed.
6, Q: If I want to put pictures on the Internet, what format should I use?
A: Any resources placed on the network are best based on the principle of being as small as possible, because that can provide viewers with faster browsing speed. If pictures on the Internet are only used for on-screen display, it is better to use JPEG or GIF. , 72dpi resolution is enough. If it is used for other purposes, such as outputting a film or a printing plate, it is packaged and compressed using a prescribed format and then transmitted on the Internet.
7. Q: How can I make full use of the digital camera?
A: As long as the resolution and size meet the requirements, images obtained with a digital camera can usually be used well for print output.
Digital camera's vertical resolution / 300 = the height at which the final image is output at 300 dpi
The horizontal resolution of the digital camera/300 = the width of the final image when outputting at 300 dpi.
If your digital camera has a resolution of 1400pix x l800pix (approximately 2.5 million pixels), calculate the following formula:
1400/300=4.67in (height), 1800/300=6.Oin (width);
This digital camera can shoot photos with a photo size of 4.67in X 6in at 300dpi. If your photo size is so big or smaller, the digital camera is enough, otherwise you will need to change a digital camera.
8. Q: Is it better to use digital photos or scan film images when making plates?
A: In the case of both are interchangeable, but in the following situations, digital photos should be given priority for time or cost considerations: when the production target includes many small-size pictures; the pictures need to be combined When a more complex product is manufactured; the customer requests immediate shipment and the production cycle is short.
9. Q: What kind of image format should I use? EPS, TIFF, JPG or GIF?
A: GIF is the most commonly used format for outputting images to web pages. It uses LZW compression and is limited to a color range of 256 colors. The image size is small. JPEG is one of the most commonly used image formats. It uses a lossy compression format and is supported by most graphics processing software. If you do not require high image quality and require storing a large number of pictures, using JPEG is a good idea, but it is better not to use JPEG format for image output. TIFF was originally developed by Aldus on the Mac to standardize scanned images and is the most extensive image printing and output format across the Mac and PC platforms. TIFF can use LZW lossless compression to reduce the image volume. EPS is also one of the important formats in our image processing work. It is widely used in graphics and layout design in Mac and PC environments and is used for printing output on Postscript output devices. In order to get the best color effects and image sharpness, printers generally require the use of TIFF or EPS format images. The JPG image quality used by digital cameras is generally higher, so it can also be used for printouts.
10. Q: Can I use color text?
A: The printing process is not as perfect as we would like it to be, and the slightest misprinting can cause four-color inks (CMYK) to fail to perfectly reproduce text and inverted white text on a colored or black background. This deviation can make subtle text blurry. Unclear. If you really want to use colored text, it is best to use one of C, M, or one of black or black. When the text font is large enough, you don't need to worry about what color it is because it can be printed accurately.