#3460- Open Prepress Interface (OPI) and Linking Bitmaps Externally

While Corel® does not manufacture Open Prepress Interface (OPI) software, or include it in any of
our  applications, we do offer OPI support. OPI describes PostScript-language statements that allow
CorelDRAW™ to use low or medium resolution images for layout and proofing, then use a prepress
system or OPI server to substitute a high resolution TIFF or other image when the final film is
imaged.

The OPI workflow protocol addresses the problem inherent with any electronic graphics production
environment - the large amount of data in image files and the productivity losses that result from
manipulating those large files within a software application.

OPI is practical for documents that contain a large amount of images and follow established
workflow and production lines. It is intended for use by professionals who design page layouts
in-house but use service bureaus to perform image scanning, color correction, and other tasks. It is
not intended for users who want to do their own image scanning, editing, and color correction with
desktop tools.  For these users, CorelDRAW™ 8 allows you to link to bitmaps stored elsewhere on
the hard drive without using OPI software. 

Originally, image-replacement systems were used to link pages and type to prepress systems. The
OPI standard was established in 1989 as a way to avoid handling huge color-image files. These files
were used as placeholders for high-resolution files that were stripped into the document or page
layout later on. 

*Note: Most OPI systems limit modification of the embedded image to cropping, resizing or
rotating.


OPI with TIFF (Tagged Image File Format) Files
OPI with TIFF files has some limitations. TIFF is a flexible format used primarily for
continuous-tone images such as photographs, but the files are rectangular and cannot convey
information about irregular borders, masking, or clipping paths. 

In CorelDRAW, ensure to enable the Link To High Resolution File For Output Using OPI check
box when importing your TIFF files. These TIFF images become known as OPI images. 

To proof a file that contains OPI images on a device that doesn't have the high-resolution files (e.g., 
your desktop printer), disable the Maintain OPI Links option in the Options Tab of the Print Engine.

CorelDRAW 8 allows linking to bitmaps stored elsewhere on your hard drive without using OPI
software.

OPI with DCS Files
OPI also supports Desktop Color Separation® (DCS) for handling color separation files. These files
are created in Corel PHOTO-PAINT™ - the filter is not available from the CorelDRAW user
interface. If sending a .DCS file to act as the low-resolution placeholder, be sure to inform the client
to resolve the DCS links using the Resolve DCS Links setting in the Print Engine. If the files are to
be stored on an OPI Server, the setting should be DCS Resolve=False. If the files are stored on a
local hard drive, the setting should be DCS Resolve=True. The option is available for PostScript
devices only.

The EPS (Encapsulated PostScript) file format that is used by DSC has an advantage over TIFF files
since it supports information about irregular borders, masking, or clipping paths. When DCS is
selected, five EPS files are generated to produce color separations. The saved file is a four-plated
image cyan, magenta, yellow and black (CMYK) plus one master OR V.2 file and a thumbnail of
the image for previewing. 

The color separations create large and complex files which consume a large amount of hard drive
space. For this reason, these files are usually stored on a separate server and linked to the page
layout file by OPI software. Remember, DCS files are pre-separated before page layout work
begins.  When job parameters, such as what press is to be used for output, are changed, it may be
necessary to separate the image again. 

OPI systems that support DCS store the color separation files on the server so that the application
does not have to transmit these large files during the printing operation. The application sends the
path information to the separation files, and these files are sent from the server to replace the FPO
image.  Once the low-resolution FPO image is placed into the page layout file and the image is sent
to print,  the Corel application sends the OPI statements instead of the FPO image. The imagesetter
produces separations with the swapped-in color separations files. 

CorelDRAW and OPI software such as Colorcentral® can embed this information in an EPS file so
that the low resolution placeable header is all that is present within the document. The
high-resolution file is swapped in at print time - acting independently of the application and
document the low-resolution EPS file resides in. Here is a sample of embedded code in an EPS file: 

       %%BeginOPI: 2.0
       %%ImageFileName: (D:\\Images\\DuomoInput.tif)
       %%ImageInks: full_color
       0.000000 0.000000 translate
       482.885625 327.061580 scale
       /OPIimage /image load def
       %%BeginIncludedImage
       %%IncludedImageQuality: 2.0
       %%EndIncludedImage
       %%EndOPI

Selecting An OPI System
If you plan to use OPI or buy a system for your service bureau, there are several issues to consider:

Supported File Formats - Some supported formats are Scitex CT; RGB TIFF; CMYK TIFF;
DCS; four-color EPS; Photo YCC; and PICT. 

Clipping Paths - Make sure the server can correctly handle clipping paths that are applied to
 images. 

Color Management - Some OPI systems utilize color management, so that the FPO
low-resolution files have the color characteristics of the final image. This can save you time and
money at the printing press, and you may avoid a few sets of proofs. 

Image Manipulation - Does the OPI system handle changes made to the work? Can it
properly support rotation, skewing, resizing, and objects inserted over images? Be certain that
the system offers the support needed in these areas. 

Using Low-resolution FPO Files - Some OPI systems allow a variety of resolution, line-screen,
and format options for the FPO file in order to give you optimal output on your in-house color
printer. Make sure the low-resolution images are compatible with your system and work habits.

Cross-Platform Compatibility - Make sure you know what file types the OPI system can use,
and that it can recognize file created on various platforms. 



Statements and Definitions
OPI statements in the CorelDRAW file are generated by the application and conform to current OPI
Specifications. These statements will be read by the OPI server. The server can be defined as any of
the following: any software package that can read OPI statements and substitute high-resolution
images at print time, an OPI-capable print server running on a file server, a prepress workstation, or
a specially modified PostScript RIP like the Linotype Hell Delta.

OPI Statements
One set of OPI statements should replace each embedded image within the CorelDRAW file. The
OPI statements specify the name and position of each image, as well as describing links to the
high-resolution image on the server, image cropping information, size, rotation, color, and other
image placement and manipulation information. 

Here are some OPI statements generated by CoreDRAW:

       %ALDImageFileName: R:\Colorcentral\Images\avrologo.TIF
       %ALDImageDimensions: 1134 689
       %ALDImageCropRect: 0 0 1133 688
       %ALDImageCropFixed: 0.00 0.00 1134.00 689.00
                   %ALDImagePosition: 197.50450 69.52309 197.50450 267.95509 524.09650
            267.95509 524.09650 69.52309 
       %ALDImageType: 3 8
       %%BeginObject: image
       %%EndObject 


Syntax (**** denotes statements not generated by CorelDRAW)

             %ALDImageFileName: [filename] Required Statement.
Records the name and path of the image (TIFF file) as it was imported into CorelDRAW or
Ventura.  The Corel application will utilize the standard form for the operating system platform it is
operating on.
             Example: %ALDImageFileName: R:\Colorcentral\Images\avrologo.TIF
Embedded spaces and other Windows naming conventions are supported without requiring
parentheses around the string. The statement line including path and filename may not exceed 255
characters. The statement can be extended using the standard "%%+" convention. OPI software
should allow for an automatic match between low and high resolution versions of the image if the
image names are similar. 

             %ALDlmageID: [filename] Optional Statement.
An identifying string used by an OPI Server to identify the high-resolution image residing on the
OPI Server. This information is stored in the TIFF file as part of a reduced-resolution image, as Tag
#32781 (Ox800D). The TIFF data type is ASCII. The TIFF 6.0 specification describes TIFF data
types and the structure of a TIFF file.
             Example: %ALDlmagelD: avrologo
This statement may be used in conjunction with the %ALDImageFileName statement to point to the
high -resolution image on the OPI server. 

             %ALDObjectStatements: [text] Optional Statement ****
Provides information to the OPI server on how the image should be treated. Described with ASCII
text and can be extended to multiple lines using the DSC "%%+" convention.

             %ALDlmageDimensions: [pixelswide] [pixelshigh] Required Statement
Image dimensions of the embedded file are described in pixels. This statement is used in conjunction
with the %ALDImageCropRect statement to relay image-cropping information to the OPI server.      
Example: %ALDImageDimensions: 1134 689
                   
             %ALDlmageCropRect: [left] [top] [right] [bottom] Required Statement 
Cropping permits the software application to print only the portion of the image inside the cropping
rectangle. By default, the OPI Server will use the value for %ALDImageCropRect for the entire
image.  Values are given in pixels, where left = 0, top = 0, right = pixelswide, and bottom =
pixelshigh. Left, top, right, and bottom describe the size of the cropping rectangle and its placement
on the image.  Pixelswide and pixelshigh are the parameters for %ALDImageDimensions.  The 
%ALDImageCropRect statement often describes the entire image.  The (left, top) values are the
coordinates of the upper-left corner of the upper-left pixel of the cropping rectangle, and (right,
bottom) are the coordinates of the upper-left corner of the pixel outside the lower-right corner of the
cropping rectangle. The width of the cropped area is calculated by the difference between the right
and left coordinates of the cropped area, and the height of the cropped area is the difference between
the bottom and top coordinates of the cropped area.   Example: %ALDImageCropRect: 0 0 1133
688 

             %ALDlmageCropFixed: [left] [top] [right] [bottom] Optional Statement 
This statement provides the same information as %ALDImageCropRect in floating point values.
This statement does not change the area covered by the image on the page. This statement is more
accurate than %ALDImageCropRect and can define partial pixel values for the cropping area.           
         Example: %ALDImageCropFixed: 0.00 0.00 1134.00 689.00

             %ALDlmagePosition: LLx, LLy, ULx, ULy, URx, URy, LRx, and Lry Required Statement
Describes location of printable area of the cropped portion of the image on the page (as in
 %ALDImageCropRect) , as well as scaling, rotation, flip, and skew information. Uses default
Postscript coordinates – 72 units per inch, origin at lower left, greater y values are up. Combining
%ALDImageCropRect and %ALDImagePosition will determine the scale factor in each dimension
since %ALDImagePosition specifies the location of the corners of the image itself.
Example: %ALDImagePosition: 197.50450 69.52309 197.50450 267.95509 524.09650
267.95509  524.09650

             %ALDlmageResolution: [horizRes] [vertRes] Optional Statement
Resolution values are given in pixels per inch. The resolution can be used to report to the user how
much a particular image has been scaled by comparing the values in the %ALDImageCropRect
statement, the %ALDImagePosition statement, and the %ALDImageResolution statement. 
Example: %ALDlmageResolution: 600 600

              %ALDlmageColorType: Spot Process Separation Optional Statement for grayscale images.
****
 %ALDImageColorType gives the type of color for %ALDImageColor. Separation indicates that the
image will be printed on all separations. Usually this corresponds to the "Registration" color
specified in the color palette of the software application.  If %ALDImageTint statement is zero, the
image is to be knocked out of all four separations. When "Separation" is the ColorType, the CMYK
values of %ALDImageColor are ignored. 

              %ALDlmageColor: [C] [M] [Y] [K] [colorname] Optional Statement for grayscale only.
****
C,M, Y, and K are values between 0 and 1 and determine the amounts of cyan, magenta, yellow,
and black ink to be used when printing the image. [colorname[ is a text string that names the color. 
Parentheses around colorName are recommended, and are required if blanks or special characters
are part of the colorname.
The grayscale image will be printed in shades of the %ALDImageColor value. If the specified color
is Process Blue with the CMYK value 1 1 0 0 , the black pixels in the grayscale image will be
printed with full blue (1 1 0 0), the 50% gray pixels will print in a 50% tint of blue. The white pixels
will not be printed. Default is 0 0 0 1 (Black).  Example: %ALDlmageColor: 0 1 1 0 (Red)

             %ALDlmageTint: [real] Optional Statement for grayscale bitmaps only. Default 1. ****
Describes the percentage of color to he applied to the image in a value between 0 (no ink) and 1
(solid). The value in this statement should not be confused with the CMYK values in the
 %ALDImageColor statement. The OPI Server computes the correct CMYK values when they are
multiplied by the tint value. 

             %ALDlmageOverprint: false I true Optional Statement for grayscale images. Default is
false. ****
When this is set to false, the image will knock out underlying objects on the separations.

             %ALDlmageGrayMap: Optional Statement for grayscale images. **** 
Matches color mapping within the application, and records changes made to the brightness or
contrast of the image. The application lookup table gives intensity values for each possible pixel
value, starting with pixel value 0 for black and 65025 for white.

             %ALDlmageTransparency: true false Optional Default is true. ****
This statement allows white pixels to be rendered as transparent. Transparency is specified by using
the PostScript imagemask operator instead of the image operator
                      
             %ALDlmageAsciiTag: Optional Statement
(TIFF tag number - decimal value) (TIFF field) Statement relays TIFF ASCII tag values to OPI
Server.

Working with linked bitmaps
CorelDRAW 8 allows linking to bitmaps stored elsewhere on the hard drive without using OPI
software.  Link the bitmaps when importing them into CorelDRAW. This feature allows adding
bitmaps to the drawing while reducing the size of your file. The bitmap that appears is a thumbnail
representation of the image that resides in another location. CorelDRAW includes options on
updating the bitmap and resolving the link to a bitmap.

To link a bitmap to your drawing
1.     Click File, Import.
2.     Choose a file format from the Files of Type box.
3.     Choose a drive and folder where the file is stored from the Look In list box.
4.     Double-click the folder where the file is stored.
5.     Click on the file name.
6.     Enable the Link bitmap externally box.
7.     Click the Import button.
8.     Position the import placement start cursor at the desired location,
            and do one of the following:
· Click to place the bitmap in its original size.
· Drag to place the bitmap. Use the import placement end cursor to position the image.
· Hold down ALT then drag to create a non-proportional bitmap. Remember to release the
mouse button before ALT.

To update a linked bitmap
1.     Select a linked bitmap with the Pick tool.
2.     Click Bitmaps, Update From Link.

To resolve a linked bitmap
1.     Select a linked bitmap with the Pick tool.
2.     Click Bitmaps, Resolve Link.