How to linearize the film against the rower?
For good print quality, it is critical to set and maintain the proper conditions for exposure and linearization on the output device.
Maintaining these conditions will help to obtain more accurate and predictable dot percentage values ​​throughout the gradation of the image and optimize the quality of fine prints. Use the following steps to get the stable output of film or photo paper:
1. Verify that the conditions of the developer meet the manufacturer's and supplier's requirements, including: time, temperature, chemical concentration, makeup ratio, etc.
2. Make sure all transmission densitometers are properly calibrated to read the best Dmax specified by the film supplier.
3. Exposure experiments were performed on each specified resolution, screen line, and dot shape to determine the optimal settings for the cable type and manufacturer's recommended Dmax. Make sure to run the imagesetter with the manufacturer's recommended parameters. The difference in density on one page cannot exceed 0.40.
4. Output an unadjusted, grey ash ladder or other test film from the RIP.
5. Measure all tonal values ​​on this unadjusted, plateable test film.
6. Enter the test value.
7. Verify linearization quality.
8. Determine the linearized final method and use it for production documentation.
Producing halftone images with continuous tone images
In order to copy the reflection draft, the halftone dot value should be equal to the input density value of the continuous adjustment original, so that the maximum range of the tone and gradation of the original image can be captured. Originals with a tone range greater than 1.7 may lose detail in the final print.
Tonal compression
A: Normal situation
When copying images on newsprint, there is an important option for compression. Tonal compression compresses the manuscript's range of reproduction tones (from bright to dark 0 to 3.0) to a limited range of tunable newsprint (0.1 to 1.1).
Under normal circumstances, the standard compression of ordinary photos can get satisfactory results. The general photo used for the best newsprint printing should include the entire contrast range from light to dark, making it easy to discern details. This separation of tone values ​​helps produce a good print contrast.
B: Extreme situation
Contrast-heavy photos lack detail, and areas that look bright are too dark or too dark. When you compress the tone, the contrast of the tone region becomes smaller. Therefore, it is important to capture and select images with normal contrast. Originals with high contrast will lose detail when scanned and compressed.
If the original contrast is too high, or if uneven main lighting is selected, excessive compression should be avoided in order to capture the details of highlights or dark areas. Excessive compression will result in loss of detail and make the appearance of prints more "flat".
Continuous tone reflectance density value
The Input Density Value of Continuously Graded Reflection Image in the Tonal Curve
High light 0.05 to 0.10
The middle tone is higher than the highlight part by 0.9
Darker than high light part 1.6
Total range (minus white to field density values) 1.65 to 1.70
Tone copy
The theory of tone reproduction is to successfully manage halftone dots (highlights, midtones, and shadows) at different regions to ensure that the contrast and detail of the graphic region are maximized. In order to optimize print quality, each image must be processed based on different actual conditions in order to obtain the correct gradation distribution.
The following example will explain why there are different gradation operations for different originals. The standard dot target parameters can be used as a guide for processing ordinary contrast images. For a qualified halftone copy, no loss of detail, midrange settings, darkness/range recovery, etc. are some of the key factors.
No detail white loss
Removing the printed dots in the no-detailed white area can increase the printable range between the whiteness of the paper and the overall ink saturation. One of the most common examples of no detail white is the reflection of shiny surfaces (eg, chromium on cars, jewelry, and some electronic devices).
Adjust the midtone settings
In order to optimize the copying effect of the key area in the manuscript, it will be important to adjust the midtones. The lighting conditions and the main content determine the key to modifying the success of the midtone adjustment.
Inadequate adjustment of the midtone content of the main content during the scanning process often leads to poor print quality. Even if the parameters are satisfied, the incorrect image in the middle will appear dark after printing. The setting of the midtones depends on each image itself and the body content. For darker images, highlight the middle point.
Shadow/range recovery
A common mistake in tone reproduction is to adjust the midtones without restoring the dark tone range. Since the operation of the midtone causes the dark portion to be elongated, it is important to restore the darkness to its maximum density.
The brightly-toned originals slightly increase the density of the dark shades without details, helping to enhance the contrast of the print.
Increase the degree of sharpening
In addition to tone replication, one final method of obtaining a qualified halftone is digital sharpening through software. As discussed in the photography section, the clarity of the original image is a crucial factor in the quality of newspaper printing. For most originals, using extra digital sharpening is beneficial. This work helps to enhance the sense of detail and the clarity of the image.
The degree of sharpening depends on the smoothness of the photo emulsion layer and the size of the enlargement. If excessive sharpening is used, a noticeable black and white outline will be generated.
Screen number
The industry standard for halftone reproduction is 85 lpi, however up to 120 lpi screen lines can be considered to improve image quality. Fine screen lines can reduce the appearance of halftone dots, provide more details, prints are smooth, and the overall feel of the image tone is continuous. Since a higher number of screens will result in insertion of dark areas, it is necessary to consider an additional 5% to 15% of dot gain in the middle of the three-quarter tone. Restore the shadow range to normal parameters for maximum contrast.
Final output
If the SNAP parameter is used, the screening tone value will meet the values ​​listed in the table below.
Black-and-white and monochrome tone tones
Color Tone Offset (85lpi) Offset (100lpi) Flexo (85lpi) Emboss (72-85lpi)
Specular reflection / no detail 0% 0% 0% 0%
High light 3% 3% 5% 8%
Quarter Tone 18% 16% 15% 18%
Halftone 35% 32% 35% 36%
Shadow 85% 85% 85% 85%
Color tones for four-color images
Crimson Red Yellow Black Level
Offset printing (85lpi)
3 1 1 0 Highlights
20 14 14 0 Quarter Tone
38 30 30 10 Midtones
60 50 50 80 Shadow
Offset printing (100lpi)
5 2 2 0 High Light
20 14 14 0 Quarter Tone
36 28 28 10 Midtones
60 50 50 80 Shadow
Flexo (85lpi)
8 5 5 0 High Light
20 14 14 0 Quarter Tone
38 30 30 10 Midtones
65 55 55 85 Shadow
Embossing (72-85lpi)
8 5 5 0 High Light
20 14 14 0 Quarter Tone
38 30 30 10 Midtones
58 47 47 86 Shadow
The values ​​in this table refer to documents processed by GCR (ash component replacement) or UCR (background color removal) and films and plates obtained from such documents.
TAC (Total Area Coverage) of the largest dark tone area
Film Features Offset Flexo Printing
TAC up to 240% 260% 240%
The minimum ink coverage in dark areas is 220% (preliminary tests may show slightly lower values) 220% (same as right) 220% (same as right)
Random screening recommendation, prior consultation Not recommended Not recommended
Excessive TAC is suitable for areas less than 1 inch in diameter and ensures that all aspects understand that the area will be printed as a field. Do not exceed 260% for areas less than 1 inch in diameter, and ensure that all areas understand that the area will be printed as solid. Do not exceed 280% Not recommended
Medium TAC in the darkest shaded region For any color plate, at most one color can be printed as solid (100%), and the two second colors should not exceed 75%. For any color separation sheet, at most one color can be printed in solid (100%), and the two secondary colors should not exceed 75%. Black cannot exceed 90%. For any color separation sheet, at most one color can be printed as solid (100%), and the two secondary colors should not exceed 75%