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HELIOS ImageServer User manual |
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ImageServer 2.5 supports backward compatibility to EPSF and TIFF layout files that have been generated by previous EtherShare OPI versions.
EtherShare OPI 1.x will not be able to handle and understand layout files generated by the new ImageServer 2.5, EtherShare OPI 2.x, however, will (with the exception of the new features and the new supported file formats, e.g. PNG and BMP).
Please note that if you are using old EtherShare OPI EPSF layout files, downsampling, color matching and other new features will not be supported when you print separations. In that case, you have to generate new layouts from the high-resolution original images and thus create layout files that can be subjected to all features available in the new program version 2.5. You may use the HELIOS "touch" program for regenerating layouts (detailed instructions are given in 5.5 "Refreshing layouts using the "touch" program"), or the HELIOS "opitouch" UNIX command (see 6.3 "The "opitouch" program").
An image file is defined by its file format. In addition to that it contains information about its color mode and the mode of compression. These three characteristics depend on one another and may not be combined at discretion. An example for that is given in the following illustration.
Fig. 2 shows a Photoshop CMYK image, the file formats that are available for CMYK images, and the fact that the Scitex CT format, e.g., cannot be compressed (options that are not available are displayed gray in the illustration).
Important: Please note that some file formats already include compression (e.g. JPEG).
- Give you a complete list of the file formats that are supported by ImageServer 2.5
- Describe the advantages/disadvantages of the formats
- Discuss the different modes of compression
The new ImageServer 2.5 provides OPI facilities and - in addition to that - contains built-in color management features. The software accepts different file formats for the generation of low-resolution layout files and it supports various file formats for color matching. Please note that some file formats in connection with specific color modes allow the generation of layout files, but do not allow color matching.
The Image Server 2.5 now allows file sizes up to 8.3 million TB (64-bit). The old 32-bit support can only handle files up to 2 GB. This is important because image files sometimes exceed 2 GB.
Table Table 1 lists all supported file formats for the generation of layout files (and the possible color modes behind), whereas Table Table 2 only lists those file format/color mode combinations that allow color matching. If you want to achieve predictable color results on your printouts, you should select for your image files one of the file formats listed in Table Table 2.
Before you save an image in an image processing application (or scan system), you should make a decision on the file format you want to choose. The advantages and disadvantages of the different file formats are described below.
Important: Again, the file formats have to be judged from different points of view. Some characteristics of a given file format may be advantageous in general and for OPI processes but - at the same time - disadvantageous with regard to color matching!
The format you choose for an original high-resolution image file already determines the format of the automatically generated layout file. Please refer to 3.2.6 "File formats of OPI-generated layout files" for explanations on the different layout file formats.
- Advantages
- Many scan systems and image processing applications can generate TIFF files. Thus, they become - in principle - OPI-compatible
- TIFF files can be edited by all popular image processing applications
- TIFF files are independent of the output device
- For TIFF files, portions of an image can be sent to the output device (in case you have selected only a specific part of the image in the layout application)
- The resolution of TIFF files can be reduced during output and thereby adapted to low-resolution output devices
- The TIFF format supports many color modes
- A clipping path that has been defined in image processing applications is preserved for printing (for details and exceptions see 3.3.3 "Clipping paths")
- Advantages
- A clipping path that has been defined in image processing applications is preserved for printing (for details and exceptions see 3.3.3 "Clipping paths")
- Disadvantages
- Many image processing applications cannot re-edit EPSF files
- Complete images are sent to the output device, even if you have selected only parts of the images in the layout application
- The generation of EPSF files may already involve a given output device. In that case, printing to different printer types produces different results
- The resolution of an EPSF image remains unchanged (e.g. 1200 dpi) even if you are printing to an output device that only allows lower resolutions (e.g. 300 dpi). Thus, printing may become very slow (ImageServer solves this problem via optional downsampling)
- When printing separations the entire EPSF image must be sent to the RIP four times (ImageServer 2.5 solves this problem)
- Advantages (compared to standard EPSF files)
- Disadvantages
- The format is available only for CMYK images and requires Linotype-Hell applications
- See DCS 1 files
- Advantages (compared to standard EPSF files)
- DCS 1 files are pre-separated and are composed of several files containing the EPSF separation plates for cyan, magenta, yellow, and black. Thus, for a given color, only the file that describes this specific separation is sent to the RIP (if you are working with the EPSF format, you only have one file that contains the complete image description. This large file has to be sent to the RIP four times)
- Disadvantages
- Pre-separation is disadvantageous for color matching, because the separation plates are created for an image that has not yet been subjected to the matching process
- Composite printers, usually, are unable to handle the four EPSF separation plates at a time and thus cannot produce a composite printout
- Advantages (compared to the DCS 1 format)
- Disadvantages
- See DCS 1 files
ImageServer supports several file formats for the generation of layout files, even if the data contained in these files have been subjected to compression. The original high-resolution files remain compressed but - usually - do not pass on the compression to the layout files. If you want the layout files to be compressed as well, you may use EtherShare Admin or the respective UNIX parameters (see 4.3 "OPI server settings" and 6.2 "The "layout" program" for details). Table 3 lists various modes of compression supported by ImageServer 2.5 and indicates whether or not they can be applied to the different file formats.
a) This mode of compression is allowed but will cause
restrictions: raster-based data are no longer recognized by
ImageServer.
The layout files that are generated by the OPI software are either EPSF or TIFF, depending on the color mode and file format of the high-resolution original image.
- the high-resolution original image is an EPSF, ICS, PDF, or DCS image or
- the high-resolution original image is not an EPSF, ICS, PDF, or DCS image, but shows one of the following characteristics:
- is not a Multichannel image and
- does not contain additional color channels and
- does not contain a clipping path and
- is not an EPSF, ICS, or DCS image
In the following, we briefly discuss the differences between EPSF and TIFF layout files. Knowing these differences can help you decide which layout file format you want to use (You may then select an adequate color mode and file format for your high-resolution original images and thereby indirectly determine the desired layout file format).
- EPSF files do not allow source cropping. If you crop an image in a layout application, this does not reduce the amount of data that is sent to the print server, because you can include only complete EPSF layout files into a print job. This is different if you are using TIFF layout files and then crop the images. In that case, the print job will only contain the data that describes the visible part of the image.
- Many applications - even on different platforms - are able to place EPSF layout images. Thus, these applications automatically become (quasi-)OPI-compatible (compare paragraph Layout applications in 3.3.1 "OPI-compatible applications").
Important: EPSF files are not identical for Macintosh and Windows computers. In fact, PC-EPSF layout files may cause problems if the high-resolution original images include a clipping path (see also 3.3.3 "Clipping paths").
In most cases, it is convenient and sensible to accept the default EPSF or TIFF layout file format. Nevertheless, you may as well choose any other format for your layout files. 5.3 "Defining folder specific OPI settings" explains how to set custom settings on a "per volume" or "per folder" basis.
The color modes of the high-resolution originals are not passed on to the layouts. By default, layout images are Euroscale- or SWOP-CMYK, to allow the layout applications to print separations. In special situations, you may also select the RGB or Lab color mode for layout images (for details see paragraph Layout Color: in 4.3 "OPI server settings").
- Scan systems, image processing applications, or similar programs that are able to generate one of the image file formats which allow the generation of layout files
- Layout applications that allow importing layout files and are able to generate OPI comments
Most scan systems and image processing applications are OPI-compatible as far as the "input" side is concerned. They all offer the possibility of creating at least one or two of the file formats that are supported by ImageServer 2.5 for the generation of layout files and for color matching (e.g. TIFF-RGB or raster-based EPSF-CIE-Lab). One of the most frequently used image processing applications is Adobe Photoshop - ImageServer 2.5 supports the Photoshop Native format.
Strictly speaking, OPI-compatible layout applications have to meet two different demands: they have to be able to import/place layout images and they have to be able to generate OPI comments according to the Adobe OPI standard and place these comments into the PostScript that is generated for each print job.
There is, however, one exception from this rule: layout applications that are able to import EPSF layout files are quasi-OPI-compatible, even if they do not generate OPI comments. This is due to the characteristics of EPSF layout files which simply do not allow applications to modify their contents. If an EPSF layout file already contains OPI comments - e.g. a reference to the location of the original high-resolution image file - these comments are preserved and passed on to the PostScript file.
Note: Some layout applications that are fully OPI-compatible also offer OPI options in their print dialogs, namely "Omit TIFF" and "Omit TIFF & EPS", and thus provide additional possibilities of speeding up print jobs when working with OPI. Details about the "Omit -" options are given in 5.7 "OPI print options - include or omit images".
The most frequently used layout applications that are - in principle - fully OPI-compatible are listed in Table Table 4.
Other applications like TrapWise, PressWise, CorelDraw, Illustrator, FrameMaker, Word and Ventura Publisher may also be involved in the process of creating documents that include text and images. They are, however, strictly speaking, not designed for layout purposes in prepress environments. These applications are - if at all - only quasi-OPI-compatible,when they use EPSF layout files.
The mentioned restrictions are also applicable to layout applications for UNIX systems. Most of these applications (e.g. FrameMaker for UNIX) are able to import EPSF layout files, and thus can be used with ImageServer 2.5.
Different layout applications provide different features for image modifications. So, depending on your application, you can e.g. place, move, scale, rotate, skew, reflect, tint, crop your images, and apply a clipping path, or overprinting. All these modifications are supported by ImageServer 2.5 and are automatically applied to the high-resolution original images during printing.
Important: Transparency definitions for grayscale and color images are the only modifications that are not supported by ImageServer 2.5, due to limitations in the OPI specifications.
If you print from a layout application, the OPI server requires different information about the images that are included in the document. There are several OPI PostScript comments that contribute to a complete image description. Some comments only serve to clearly identify the high-resolution image; some of them are used to describe the modifications that have been applied to the layout.
For example, the comments "%ALDImage Dimensions" and "%ALDImagePosition" define the dimensions and the position of an image, and thus may also include information about whether you have moved or scaled the layout image.
The behavior of clipping paths in connection with OPI varies, depending on the file format and page layout application. Difficulties may occur if you apply clipping paths to a TIFF image file or if you are using the PC-EPSF format.
Clipping paths can be applied to TIFF images in an image processing application. Even though the image will print correctly and the clipping path will be applied, some applications cannot display a TIFF clipping path, and hence are unable to properly use features such as text "Runaround". Therefore, by default, ImageServer 2.5 generates EPSF layout images of TIFF high resolution files that contain a clipping path. Layout applications can then properly display and utilize the clipping path (unless your system generates PC-EPSF layouts).
If your layout application does support the TIFF clipping path feature, e.g. QuarkXPress 4.1/5 or InDesign 2, then you can use either EPSF or TIFF layout images. Some applications also have the capability to add or modify the image clipping path. If you wish to take advantage of this feature, then layout images should be generated in TIFF format (see 5.3 "Defining folder specific OPI settings"). In addition, you need to specify whether to use the clipping path applied by the image processing application, or the path applied by the page layout application. See 3.3.4 "Application clipping path (EtherShare Admin)" for details.
Unlike Macintosh-EPSF files, PC-EPSF files contain a TIFF screen preview of the respective image (instead of a PICT).
The layout application uses the PC-EPSF included TIFF screen preview for the monitor display. ImageServer 2.5 defines the value white to the area of the rectangle that has been clipped away, so that applications like QuarkXPress can apply the "Runaround" feature after placing the layout image. Thus, if you generate PC-EPSF layout files, even if the image has a clipping path with a shape other than a rectangle, it will be printed correctly.
Note: For the generation of PC-EPSF layouts see
4.4 "Volume settings".A bitmap image file that already contains clipping path information and then has clipping path changes applied in a layout program, may cause interferences and lead to unwanted results. EtherShare Admin offers a new option (see checkbox Ignore mask for bitmap images in Fig. 3 below) that makes the server ignore existing masks for bitmap images so a clipping path can be defined from within the layout application (QuarkXPress, InDesign, etc.). This option can also be set for individual folders via folder naming syntax (see 5.3 "Defining folder specific OPI settings").
ImageServer recognizes and supports additional channels (e.g. Hexachrome®, spot colors, or alpha channels). At present, ImageServer 2.5 will use all additional channels as spot color channels.
It is often required to ignore additional channels and use the default printing channels, e.g. CMYK, RGB, CIE-Lab. Many layout applications ignore additional channels in order to be compatible with the printout. Printing from these applications, ImageServer can ignore additional channels (see checkbox Ignore additional channels for bitmap images in Fig. 3) server-wide or enable/disable this setting on a folder tree (see 5.3 "Defining folder specific OPI settings").
ImageServer requires PostScript output devices for printing. There are three types of PostScript RIPs, namely Level 1, Level 2, and PostScript 3 compatible devices.
The Level 2 and PostScript 3 specifications follow the Level 1 specification and provide many more features, as e.g. support for different color spaces such as CMYK, RGB and CIE-based color spaces, and provisions for color mapping and transformations into CMYK.
Different printers may behave differently and provide different features. PPD files contain comprehensive printer descriptions - with the supported PostScript level being only one aspect. ImageServer (just like any application) refers to the PPD file to get information about the features of the output device. So, for high-quality printouts, always make certain that you have activated a PPD file that properly corresponds to your current output device. For details, see also your EtherShare documentation.
Usually, if you are printing with ImageServer 2.5, our software takes care about the separation into CMYK. The separation modules of the RIP are not required. Thus, print jobs do not depend on the final output device. It does not make any difference whether you are using a Level 1,
Level 2, or PostScript 3 printer.
It is, however, possible to leave the separation to the PostScript RIP. In that case, you have to select the Lab D65 color space as output color space (compare Default Printer Profile: in 4.5 "Printer queue settings") and you have to have a Level 2 (or PostScript 3) output device. The RIP will then be initialized with a specific color rendering dictionary (CRD) and, using this dictionary, will perform the separation into CMYK. This workflow may be sensible if you are sending your documents (e.g. a magazine) to different production sites. Your print job is not yet separated for a given output device and the Lab D65 color space is device independent. The different RIPs transform the color data into the gamut of the respective printer/or press and the output results should all be identical. Please note that this workflow does not allow proof printing (see A 2 "Colors, color matching, proof printing - basic concepts" for details about proofs).
If you retouch an image using an image processing application, you also define a color mode for this specific image. This color mode will be preserved as far as the high-resolution original image file is concerned - but it will not be passed on to the layout file and it may be changed for printing purposes, i.e. transformed into the color space of the output device.
In the following, we briefly describe how ImageServer 2.5 handles or modifies color modes and thus relieves you of taking care about it.
The color mode OPI selects for printing is dependent on whether you print composite or separations and on whether or not you have activated color matching. The color mode of the high-resolution original image does not matter, unless it is Bilevel or Grayscale - these two color modes are preserved for printing.
- Printing composite (without activating color matching):
Images that are printed as rastered images are transformed into the color space that is specified as CompositeColorspace (default is CMYK). See "psresolve" in the HELIOS Base manual for details.
For other images, color spaces remain as they are.- Printing composite (if color matching is active):
For all images that are printed as rastered images, OPI uses the color space that is specified in the printer profile. For other images, color spaces remain as they are.- Printing separations (without activating color matching):
For all images that are printed as rastered images, the color space is CMYK. For other images, color spaces remain as they are.- Printing separations (if color matching is active):
For all images that are printed as rastered images, OPI uses the color space that is specified in the printer profile. For other images, color spaces remain as they are.It is up to you to select a color mode for layout files. You can choose between CMYK, RGB, and Lab (compare Layout Color: in 4.3 "OPI server settings"). By default, OPI sets the Euroscale CMYK color space for layouts, to allow the layout applications to print separations.
The settings for color matching may be different for every printer queue you have defined on your server. In principle, you activate the ImageServer CMM (Color Matching Module) by selecting an ICC printer profile for the respective printer queue (see also 4.5 "Printer queue settings").
In some specific situations, however, ImageServer 2.5 performs color matching "behind the scenes", even though it had not been activated explicitly. These situations are described below (please remember that you may not delete the "ICC-Profiles" volume, because this would disable indirect color matching and it would at the same time entirely disable OPI).
- whenever OPI transforms an image into another color space (see also 3.5 "How the ImageServer modifies color modes").
- for all Lab images, because they always have to be transformed into RGB or CMYK (unless you are working with Lab layouts and explicitly choose "Lab D65" as output profile - compare chapters 4.3 "OPI server settings" and 4.5 "Printer queue settings").
- for all Multichannel images (Hexachrome®, HiFi Color, etc.). For these images, there are no standard profiles OPI can refer to. Therefore, you are forced to specify an ICC printer profile and thus activate color matching.
For proper color matching ImageServer needs an ICC profile on the output side (printer profile) and an ICC profile on the input side (image profile). This means that you need to tag an image profile to every high-resolution image you want to print with predictable colors, and you have to make sure that your layouts are tagged in case you want to print layouts (see also 5.4 "Tagging images with ICC profiles").
Whenever you print a document from a layout application, the OPI software has to locate and find the images that are to replace the low-resolution images you have used for layout purposes. These images, that are required for replacement, may be either high-resolution originals, or the layout files again (in case you print your documents with layouts).
If you do not use the layouts at all, but import high-resolution images into your document, there will be no image replacement for printing unless you set the Replace Images option to All for your current printer queue (see also 4.5 "Printer queue settings").
Important: Remember that if you want to use OPI from a Windows system, you should always maintain the 3-character file name extension. The extension may be any extension that is supported by Photoshop for Windows.
ImageServer 2.5 offers complex finding strategies for image replacement. The software is able to locate images even after you have moved or renamed them - as long as they remain on server volumes.
- First of all, OPI will check the folder that contained the image file during layout generation.
- Secondly, the software will disregard the ".lay" extension and the "layouts" subfolder of the folder that contains the placed image and then check this folder.
- After that, OPI will check all image search paths you have defined using EtherShare Admin (see 4.3 "OPI server settings"). These search paths help the OPI software follow up images you have moved after layout generation.
- Finally, if a high-resolution file cannot be found with the methods described above, OPI will try to resolve - with the server desktop data base - the Macintosh file ID, which has automatically been saved in the low-resolution file during layout generation. With this method, it is possible to find image files which were renamed and/or moved on the same volume (in case the EtherShare server desktop data base is outdated, searching via file IDs may find the wrong image. With the "psresolve" command, you can switch off image replacement by file ID using the ImageIDsearch parameter. For details see "psresolve" in the HELIOS Base manual).
Please note that the finding procedures are started automatically during printing. If you want OPI to report missing image files, you have to activate the Check Images option when setting up the print preferences (compare Fig. 10 in 4.5 "Printer queue settings"). Missing images will then stop the print job. With Check Images switched off, the documents will be printed, but the printouts will show blanks where images could not be found.
Note: You may use the EtherShare "Error Queue" feature to save and restart print jobs that have produced an error message (compare Fig. 9 in 4.5 "Printer queue settings" and your EtherShare documentation).
| © 2002 HELIOS Software GmbH |
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