There's a trick to handling this kind of printed image! 4 easy steps to get it done
As the saying goes, even a skilled cook can't make a meal without rice. To print good images, you not only need good image-editing skills but also high-quality originals, so choosing the source of your images is especially important. We have strict standards when selecting newspaper images:
First, the image brightness needs to be suitable. It's best not to choose originals that are too bright or too dark, otherwise, processing them will be difficult and the results won't be good.
Second, the image saturation should be appropriate. It's best not to choose images with color cast or low saturation, because merely trying to fix them later won't be enough to achieve ideal results.
Third, the image information must be complete. You shouldn't have missing parts of people in the image.
Fourth, the best image format is RGB mode, as this mode contains rich information. After processing, you can convert it to the CMYK mode suitable for printing, minimizing information loss.
Fifth, analyze the image content and focus on key points. If the image mainly features people, pay attention to skin tones, as different races have different color characteristics. Focus on the key points; if it features landscapes, pay attention to contrast, layers, and saturation; and if it's a painting or calligraphy, pay attention to tone and contrast.
Generally, the quality of printed images is determined by their output resolution. In newspaper printing, the image output resolution should be 1200dpi × 1200dpi. According to the relationship between image resolution, output resolution, and output image size-output size = image resolution ÷ output resolution-the larger the size of the printed image, the higher the pixel count you need when capturing it. Only then can image quality be guaranteed. For example, a 6-megapixel image (containing 6 million pixels, which can be squared to get horizontal or vertical resolution) has roughly 2500dpi × 2500dpi information, so the printed image size would be approximately 2500 ÷ 1200 = 2.1 inches, or about 5.3 cm.
From this perspective, for images downloaded from the internet, you should choose the largest possible size because it contains more pixels. You can compress them during processing to ensure higher output resolution for newspaper printing, improving print quality.
Technical Processing
To ensure the quality of newspaper images, processing related images is absolutely necessary. In general, for people (especially national leaders), cultural relics, and paintings, the images must be faithful to the original and not changed arbitrarily. But defective images should be reasonably retouched, and artistic effects can be appropriately applied. Considering that newspaper images are roughly divided into portraits and landscapes, we'll explain them separately.
01/ Technical Processing of Portrait Images
For portrait images, you should be clear about the image format, content, exposure, and color cast, and based on this, perform image processing. Specifically, you can do the following with images provided by editors:
First, adjust the image globally in RGB mode. Generally, portraits should maintain good brightness and clarity, with colors as vivid as possible, enhancing the main color and reducing the opposite color. Therefore, if the image is underexposed, increase the brightness; if overexposed, decrease it. If the overall color is off, adjust the corresponding hue values. If the colors are too dull or too vivid, reasonably increase or decrease saturation.
Second, adjust the image locally in RGB mode. For areas that need local adjustments, create a selection and make adjustments within that area, following the same criteria as the first step.
Third, check the image's tonal range. You can open the image in Photoshop and check the highlights and shadows. It's best if the RGB values in the highlights and shadows are between 0 and 255, generally between 5–250 is excellent. If it doesn't meet this standard, make reasonable adjustments. Figure 1 shows the image information window in Photoshop.
Figure 1: Image information window in Photoshop
Fourth, adjustments are made under CMYK mode. After the previous three adjustments, we can convert the image to CMYK mode and start adjusting the depth. First, adjust the character's skin tone. For Asians, the main CMYK values of a character are magenta and yellow, with yellow being about 10% higher than magenta; Blue is the secondary color; black should be rare, sometimes none. The front of the face is generally no more than 30% magenta, and the deepest dark areas of the face do not exceed 70%. Blue and black are indispensable colors for the face, but they can easily dirty newspapers, so their percentages should not be too high. Generally, cyan is more than one-third less than magenta, and black is much less than magenta. Then comes the costume. The key leaders in the Party newspaper photos are all dressed in dark suits or white shirts. For white shirts, white is naturally the main tone; magenta, yellow, and black should be minimal and basically absent; For dark suits, the main tone in the image is cyan with magenta and yellow as secondary colors, and black as a supplementary color. Generally, in the gray balance data for dark suits, blue is about 10% more than magenta and yellow. The black version is mainly used to show the layers of the image. When adjusting, control the amount to ensure the clothing colors are normal. Again, the background color. The background of the picture should be as blurred as possible to highlight the people in the background, making them stand out more.
02/ Technical processing of landscape images
For landscape images, due to their strong overall cohesion, colors and contrasts must stand out, and the image must not be color-deviated. Since newspapers lose layers during printing, you can appropriately increase contrast when processing images.
Generally, the ideal is 240%~260%, but never exceed 260%, otherwise the plate can easily get stuck and dirty.
Compensation and correction are well done
After processing the images, it's usually time to make plates and output them. Under normal circumstances, during printing, due to pressure between the printing roller and the paper, the ink dots will definitely increase. To ensure that the finished image information is accurately transmitted to the printing stage and that images are well reproduced, linear work and a printing compensation curve must be set during prepress plate making.
Linearization correction refers to the process during CTP plate making by correcting the corresponding dot values in the process software so that the final output dot values match the original dot percentage of the image as closely as possible.
To complete this process, it is usually done by first pulling up the uncorrected linearization curve in the process software and outputting a standard plate with the test pattern. After debugging the output with a normal CTP device, the corresponding dot values on the plate are measured using the iC-Plate or other similar plate measuring instruments, and these dot values are then input into the linearization curve to obtain the corrected curve.
The same operation applies to printing compensation curves. Operators install a standard printing plate with test patterns that has not been compensated and is properly tuned for printing. This debugging includes the printer's condition, paper, ink, blanket, and other external conditions. Once all are properly matched, the machine is turned on for printing. Then, the Aiseli i1 or other reflectance densitometer is used to measure the dot percentage of the corresponding pattern on the print, and these values are entered into the printing curve to obtain the printing compensation curve. Figure 2 shows the printing compensation curve in Changliu.
Figure 2: Printing Compensation Curve in Smooth Flow
Before putting new equipment into use, linear calibration must be carried out to obtain the plate's correction curve and the printing compensation curve. After these curves have been used for a while, changes in equipment conditions often require re-measurement and the creation of new curves.
For older equipment, calibration compensation is also needed after major maintenance, such as servicing the CTP laser prism and optical path, changing the brand of developer used in the plate processor, using a new batch of plates, or replacing the printing press blanket.
Of course, some technicians combine the plate correction curve and the printing compensation curve into a single curve, which is also fine. The key is to strengthen oversight of the printing situation in daily work to avoid significant environmental changes affecting print quality.
Controlling Print Quality
During the printing process, print operators and quality inspectors need to closely monitor the print conditions on site to ensure product quality.
The same applies to images. Generally, we can judge print quality by observing the print control points. Normally, when the plate is made, control points are added to the blank edges of the plate so that the printing staff can control quality during the printing process.
These control points include 100% C, 100% M, 100% Y, 50% K, four-color composite gray, and four-color cross registration lines. By observing this information, the printing and QA staff can determine if there is any color deviation or misregistration during printing and correct it promptly.
In addition to the above control points, print conditions can also be understood by observing the colors of the newspaper's masthead. Masthead colors are usually fixed, and printing operators can compare them with the standard masthead sample to determine the color printing performance of the press that day, and then make adjustments accordingly.
In short, during newspaper printing, it's important to monitor image quality from all aspects to ensure color accuracy, stability, and consistency, ensuring satisfactory printed images.