Dolev 800 - Application Issues -
Dolev PS Excurves

Creating an Excurve
Exposing the Gray Scale and Measuring Values (Steps 1& 2)
Entering Measured Values in Excurve Table (Step 3)
Entering Excurve into Plotter Format (Step 4)
Negative Excurves

Creating an Excurve

The steps for creating and testing an Excurve are:

1. Convert and expose the gray scale under real exposure conditions using a Plotter Format. You can use an existing Plotter Format or create a new one. A gray scale file (named "grayscale") is provided in the Job/Page Public/Tables. Use a Plotter Format which does not have a defined Excurve.
2. Measure the values on film with a densitometer.
3. Enter the measured values into an Excurve Table.
4. Enter the Excurve file name into the Plotter Format used to expose the grayscale file.
   

Exposing the Gray Scale and Measuring Values (Steps 1& 2)

Exposing the grayscale file is the first step of preparing an Excurve.

A grayscale is a strip made up of 21 areas. The left most top area has a value of 0% and the right most bottom area a value of 100%. Each area increases by units of 5%

Scitex Gray Scale

The following procedure describes how to build a positive Excurve. Instructions for creating a negative Excurve are provided afterwards.

Basic knowledge of using a densitometer is assumed. Before beginning, you should make sure that your densitometer reads 0 when positioned on a transparent area of your film. If it does not, reset it to 0.

Perform the following to expose the gray scale :

Select the Job/Page Public/Tables from the Library List from Job level.

Select Start Work from the Library menu. Select the grayscale file. At this point the grayscale file is still a PS file. The PS Options menu is displayed.

Select Convert. The PS Defaults form is displayed.

Toggle the Destination parameter to Plotter.

Toggle the Set Size parameter to bounding box, since the grayscale file is an EPS file.

The Excurve can be calibrated for a CT or for a LW, depending on your preferences.

If you want to calibrate by CT values, set the LW resolution to 0 and the CT resolution to 12.

To calibrate by LW values, set the LW resolution to 60/80/100/120/140 (according to your requirements) and leave the CT resolution with the default value.

Enter the name of the Plotter Format to be used to expose the grayscale file in the Format File parameter.

Enter C (Cyan) in the Separations parameter of the Expose - Dolev form. This is the only separation you need to expose.

Select the Submit to Q <F1> function key.

Wait until a message indicates that the grayscale file has been successfully converted and exposed.

Develop the exposed film.

Use the densitometer to measure the density of the darkest area on your exposed film.

If the density reading is between 3.8 and 4.2, you may proceed. If the density reading does not fall between these values, this suggests that the laser intensity of your imagesetter needs to be adjusted and the grayscale file re-exposed. Refer to Chapter 6, Calibration to calibrate laser intensity.

Measure the dot percentage values of all 21 areas on the Cyan separation. Write the measurements directly on film using a felt-tipped pen.

Entering Measured Values in Excurve Table (Step 3)

Note: The following must be performed in the Job/Page Public/Tables.

Select the Job/Page Public/Tables from the Library List from Job Level.

Select New File from the File Types box to create an Excurve.

Select Table from the File Types box.

The Create Table form is displayed:

Create Table form

Enter the name of this Excurve in the File Name parameter. Enter an E (for Excurve) in the File Type parameter.       

Enter Y in the Separations (C, M, Y, B) to which this Excurve will apply.

Toggle to No in the Negative parameter. Negative Excurves are described on the following pages.

Select the List/Modify <F3> function key to display the List of Points form.

Note: You can change the units if desired. If left unchanged, the units remain in dot percentages.

Create Table:

Function Keys List of Points Form

Exit <F1>

To return to the Create Table form.

Add <F2>

To add measured points to the table.Change <F3>

To modify entered measured points in the table.

Delete <F4>

To remove entered measured points from the table.

1. Create table
   
2. Add New Points

Measured Values    Measured Values

on File (Sep 1... SepN)    on exposed film (sep1...sepN)

Press the Add <F2> function key to add the measured points to the table. Take the sheet of film with your exposed gray scale. For each dot percentage area, enter the "ideal" value on the left column and the value actually measured with the densitometer on the right column. For example:

Add New Points form

Function Keys Add New Points Form

Exit <F1>

To save the Excurve and return to the New Excurve (Create Table) form.

Previous <F2>

When finished, select Previous to go back to the New Excurve (Create Table) form.

Add More <F3>

You can enter up to 10 points on the form. To enter more points, select Add More. For your convenience, the first parameter is the last point added on the previous form.

Entering Excurve into Plotter Format (Step 4)

In steps 1 through 3 you have created an Excurve Table and can now enter the Excurve into a Plotter Format. You can then expose a file using this Plotter Format which uses the specified Excurve. Perform the following to enter an Excurve into a Plotter Format:

Select Set Up and then I/O Devices. Select Plotter Formats. The Dolev 800 Formats (Modify Create) List form is displayed as shown on the first page of the next section: Dolev PS Plotter Formats.

Enter the name of the Plotter Format in the Enter Format Name parameter. Select Enter. The Modify/Create Format form is displayed. This form displays the parameters of the specified Plotter Format or default values for a newly created one.

Enter the name of the Excurve Table you created in the Excurve Positive parameter.

Select Save to return to the Library screen.

Expose the grayscale file again. To do so, select Start Work; select the grayscale (LW or CT) file; select Expose (Plotter) from the CT Options or LW options menu according to the type of file. Make sure that the Format parameter in the PS Defaults contains the name of the Plotter Format that uses the Excurve Table that you defined. You can now re-expose the CT or LW previously converted from the grayscale file.
     

Develop the film and measure the grayscale file values as you did earlier.

Note: The values you measure with the densitometer should match the file values (with a maximum difference of 1%), because you are using your new Excurve. If this is not the case, start over. Unless you have extensive experience with Excurves, starting over is better than modifying.

Negative Excurves

Negative Excurves must be used for exposing negative images. Do not expose a negative image with a Positive Excurve. It is better to expose a negative image without an Excurve than with a Positive Excurve

The Create/Modify Format form contains a Positive Excurve parameter and a Negative Excurve parameter. Enter the appropriate Excurve names in these parameters so that the Plotter Format can be used for a positive or negative exposure.

The system selects the Positive or Negative Excurve Table for exposure from the selected Plotter Format according to the status of the Negative parameter in the PS Defaults form (Y or N).

If the Negative parameter is N in the PS Defaults form, the Positive Excurve in the selected Plotter Format is used. If Negative is Y, the Negative Excurve is used.

If you enter the name of an Excurve Table that does not exist, the system displays the following message:

Excurve File filename does not exist in Public/Table.

You can then either create the required Excurve Table or expose without it. If the Excurve cannot be found during exposure, the above message is displayed again and the image exposed without an Excurve.

To prepare a Negative Excurve perform the following:
      

Enter a Y in the Negative parameter in the PS Defaults form used to expose the grayscale file.

Expose the gray scale. If the gray scale has not been converted, do so before exposing.

Set hour densitometer to measure negative values. Measure each of the 21 gray areas. If your densitometer does not measure in negative, you can measure in positive and enter these values in the Excurve. If the Negative parameter is set to Yes in the New Excurve (Create Table) form, Dolev PS will automatically calculate the negative value.

If you measure a 5% area on a negative gray scale with a positive densitometer, the value will read 95%. The system will automatically convert it to 5%.

Enter these measured values in the Add New Points form as described for the Positive Excurve.

Enter the name of this Excurve in the Negative Excurve parameter in the Create/Modify Format form.

Expose files using this Plotter Format.