Obtaining high quality images

If you want to win customers, you must make high-quality images. Calibration photosetters are a crucial part of this.

It is difficult to obtain high quality dots using an unaligned imagesetter, and it is not difficult to calibrate the imagesetter with the proper tools. In this way, if you want 20% outlets, the result should be 20% instead of 16% or 23%.

In addition to accurate level reproduction, correct alignment of the imagesetter can also help you avoid the highlighting and darkening of highlights.

With the film from the imagesetter, the exposed part is black, and the unexposed part is transparent, with no change. The word “density” is used to measure the degree of blackness of the exposure, which is the result of a logarithmic operation. The greater the value, the greater the degree of blackness. The maximum density of a medium is counted as Dmax.

To measure the degree of opacity or darkness of the film base requires a special densitometer. There are two basic types of densitometers, densitometers are used to measure film density, and densitometers are used to measure print density. Of course, there are also densitometers that have both functions. The densitometer should be calibrated before each calibration.

The density of the output film depends mainly on the setting of the exposure machine exposure value. Most photocomposing machines can control the intensity of the laser beam. The higher the laser intensity is, ie, the greater the exposure value, the darker the output image is, ie, the higher the density.

To obtain high-quality output, you must choose a suitable exposure intensity that can express pure black text with sufficient density and accurately represent the tone image. This process is not simple, because the imagesetter cannot directly represent continuous tone images and can only be simulated with halftone screening.

The exposure intensity used to generate truly black text (generally its log density value is between 3.5 and 5.0) is likely to be too heavy for photo image copying.

If the maximum density is high, some details will be lost. Text documents lose serifs, and ash ladders tend to be heavy.

If the maximum density is low, the film that is washed out is not black enough to meet the requirements for printing.

You can adjust the exposure to meet the density requirements for text-only documents. Then you can use the imager's calibration software to generate Postscript transfer functions (lookup tables) that can be generated by the imagesetter in front-end layout design software such as QuarkXPress. Grayscale values ​​are specified in CorelDRAW and Adobe Photoshop.

However, there are many factors that affect the final output, including:

Process parameters (liquid concentration, temperature, and filming speed);

Film type and batch;

Network parameters and photosetter accuracy;

Guarantee the stability of punching process

It is important that the punching machine meets the standard workgroup parameters before calibrating the imagesetter. Variations in reagent concentration and oxidation rate or flushing time can affect the output quality. The following situations will increase the density of the output:

Increase developer concentration;

Reduce flushing time;

Maintaining the stability of the punching sheet environment is a key link and requires regular maintenance and maintenance of the punching machine. Each time after adding or replacing a new liquid, it should be recalibrated against the rower.

The optimal exposure intensity of an imagesetter depends on the type of film. Some sensitized emulsions are more sensitive to laser light and are easier to overexpose. Film thickness is also a factor to be considered. To get the best exposure value setting, the corresponding detection can be performed to generate the transfer function of the imagesetter, so that the exact dot size can be guaranteed.

Different batches of film have different performance. To ensure that only the same batch of film is used at a time, the imagesetter should be calibrated against the batch of film before using the new batch of film.

Halftone dots are determined by the imagers' accuracy and the number of screens.

The resolution of the imagesetter reflects how much the arrangement of the function controls the laser beam exposure on the film to form an exposure point. Each exposure point is formed by focusing a laser beam on the film. The exposed area will turn black when developing. The denser the exposure points are arranged, the higher the resolution, the greater the maximum density that can be obtained.

If you have calibrated the densitometer and found the proper exposure intensity, then it's time to generate the transfer function. The transfer function is actually a look-up table, and the imagesetter can use this table to ensure that the dot area ratio of the output is consistent with that specified in the front-end layout software. This process is often referred to as linearization. For each combination of film type, resolution, number of screen lines, and dot shape, a transfer function should be created separately for it.

Prepress SOLUTION's imagesetter application PrePress ToolBox is a typical transfer function generation tool. First, the uncalibrated imagesetter outputs a test sample with a typical halftone percentage of the ash ladder, then uses a density meter to measure the ash ladder, and then enters the measured percentage of the actual output dots into a dialog box, and then PrePress ToolBox A PS transfer function can be automatically generated so that the image-setter can compensate the gray-area dot area rate data received before the exposure of the film. The actual control exposure data is the compensated data.

Finally use the transfer function just generated to output the test sample and see if the required accuracy is achieved. If not, a new, more precise transfer function should also be generated based on this transfer function. This test should be repeated at regular intervals during actual production to ensure the stability of production quality.

PrePress ToolBox and Panther RIP can store multiple transfer functions, which correspond to different types of film, resolution, number of screens, and mesh. Of course, similar products from other manufacturers may also have this function.

Calibrate your imagesetter regularly and pay close attention to possible influencing factors. Your production quality will be more stable.

Source: Bison