Halftone Screening is very useful for creating customised dot pitch and angles for Rotary and Flatbed screens. Once tonal layers are ready for production, this is the final check prior to output for engraving. With various dot shapes, customised resolution and the ability to change the file size, this can be a very flexible function.
Using Halftone Screening
- Open a separated design with tonal layers and view the design in the desired number of repeats 2 x 2 repeats will suffice.
You do not need to save the design in repeat before applying the halftone screen. This helps keep the original file much smaller in size.
- Activate the first layer and go to Layer Menu > Halftone Screen. Layers must be selected individually to avoid moire effects during printing. The Halftone Screening sheet will open.
- Across and Down - these measurements relate to the number of repeats visible.
- Xres and Yres - the resolution of the output device in either DPI or DPC.
- Angle - this applies to the line angle of the dots on the screen. Each layer should have a slightly different line angle to all the others.
- Frequency - this is the line spacing of the mesh. Enter the required line frequency in either LPI or LPC.
- Dot type - Square, Ellipse, Round, Cross, Line, Diamond, Hexagon, Star and Circle dots can be created.
- Resize Halftones to fit repeat - this feature zooms the screen so that it fits the destination output and repeats over the joins, pushing the dots together to make them repeat correctly.
Note: To use this feature, you must save the design as a square repeat, before proceeding, as the angle may change slightly to fit on a rotary repeat. For this option to work correctly, please follow the method ‘Producing accurate screening’.
- Adjust Resolutions for Accurate Angles - adjusts the resolution of the file to accommodate less frequently used angles. Using this option could result in very large, high resolution files, and is defaulted to be off.
- Resample back to Chosen Resolutions - resamples the design back to its original resolution following the halftone screening process of some angles.
Note: Using this option could result in loss of information following the halftone screening process.
-
Open and Save - useful if you have several standard screening set ups. Enter your screening set up in the Halftone Screening window and press the Save button. Repeat for all the different set ups you use. Use Open when you need to screen a layer and locate the set up you need. The saved screening information is automatically opened with no need to re enter specific figures as the halftone settings are remembered by AVA.
- Enter the required settings and click OK. The design will now be generated with the proportions and resolution from the window. The newly screened layer retains the name from the original layer and ‘.screened’ is added at the end of the name.
Accurate Screening
Screening will only work correctly if your measurements are exactly divisible with the resolution and size. Follow this method, to resize your single repeat so the mathematics work correctly.
- Make a small file, for example 1 x 1 inches with the resolutions set to 508 dpi (200dpc).
- Open the Info Window, set the units to mm, then go to Edit Menu > Select All and note the size of the design in mm. Leave the Info window open and go to Edit Menu > Select > None.
- Add an 8 bit layer and colour it grey.
- Hold down the ⌥ (option key) and click on the pencil icon next to the layer to change its draw level to 45% and go to Edit Menu > Fill so that you get a flat grey tint over the whole file.
- Go to Layer Menu > Halftone Screen.
- Set the Resolution to 508 dpi, the Angle to 25, and the Frequency to 100 lpi.
- Leave Resize Halftones to Fit Repeat, and New Document unchecked, and click OK.
- Zoom the design to 5000%.
- Using the Rectangular Selection Tool, start making a selection at a specific point and hold down ⇧ (shift key) to constrain your selection to a square. Drag your square selection until you have found the smallest repeat of the screening effect.
- Note the selection size displayed in the Info window. It is now possible to calculate the repeat size which is mathematically possible for your resolution and size by finding a number which is divisible by the size you just measured. For example, if your design is originally 508 pixels square, and the repeat size is 29 pixels, the closest divisible size for the design is 493 (508/29 = 17.51. Therefore 17 x 29 = 493)
- Resize your design to 493 pixels and then go to Layer Menu > Halftone Screen and screen the design at 100 lpi, 25 degrees, and 508 dpi.
All repeats will now match exactly.
- The size of the repeat is now incorrect, so resize the screen layer back to 508 pixels.
If the resize stretches the design too much, then calculate using 2 or 3 repeats instead and get the closest or exact match. Using the Repeat Window, set 2 or 3 repeats on screen and use Halftone Screen. This will generate a new file with 2 or 3 repeats in it (viewing a design in the Repeat Window and then using Halftone Screen steps up the file in a square repeat). Do not use the Step and Repeat function for this method.
Automation
Settings within the Halftone Screening Window can be made into a Palette Button, meaning these settings can be recalled any time at the click of a button. This is perfect when you use several different angles and dot shapes because it prevents you from having access the Halftone Screen window each time and adjusting the settings. The button does it all, and is easy to set up.
- Go to File Menu > New > Palette, and save the palette locally on your hard drive.
- Go to Layer Menu > Halftone Screen.
- Adjust the settings accordingly.
- Drag the Settings Handler into the palette you created in Step 1.
- Repeat Steps 3 and 4 until you have recorded all the settings you use.
- Save the Palette. Your Palette will look like this:
- ⌥ (option key) click on the title of the Palette to open its editor:
- Use the editor to rename the Palette Button to something appropriate to the settings it applies. Custom icons can also be added to further personalise your buttons.