Open Prepress Interface (OPI)

Established in 1989, Open Prepress Interface (OPI) provides a solution to one of the most common problems encountered when working in a graphic design environment: large file size resulting from the presence of high-resolution bitmaps. Most OPI systems restrict bitmap modification of the embedded bitmap to cropping, resizing and rotating.

To achieve this solution, a service bureau will scan any bitmap images using a high-quality scanner. The resulting images will be retained by the service bureau and will be stored on their OPI server. The user is then provided with low-resolution bitmaps for use in the document as For Position Only (FPO) images. Using FPO images which are linked for use with an OPI server allows the document size to remain small, increasing overall file performance. When the finished document is sent to the service bureau for output, the FPO files will automatically be replaced with those which are stored on the OPI server.

• OPI with .TIF Files
• OPI with .DCS Files
• Selecting an OPI System
• OPI Statements
• Working with Linked Bitmaps

OPI with .TIF Files

OPI allows the use of low-resolution bitmaps as placeholders for the high-resolution bitmaps that are to be used in the document when it is output. To use OPI, the Link to high resolution file for output using OPI option must be enabled in the Import dialog of CorelDRAW 12.

Using OPI with TIF images does have some limitations. TIF is a flexible file format used primarily for continuous-tone images such as photographs, but these files are rectangular and cannot convey information about irregular borders, masks or clipping paths.

When the document is received by the service bureau, the OPI server will replace the low-resolution images contained in the document with the high-resolutions ones that reside on the server. In order to do this, the Maintain OPI Links option must be enabled under the PostScript tab of the Print dialog in CorelDRAW 12. To proof a file that contains OPI images on a device that does not have access to the high-resolution files, disable the Maintain OPI Links option prior to printing.

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OPI With DCS Files

Many OPI systems also support Desktop Color Separation (DCS) for handling color separation files. If a service provides a DCS file to act as the low-resolution placeholder, confirm whether the service bureau wants to resolve the DCS links. If the service bureau would prefer to resolve the DCS links on their end, the user will have to change the Resolve DCS Links setting. This can only be done using a PostScript output device.

DCS is a 32-bit file format used primarily by service bureaus. When a DCS file is created, 5 EPS files are generated to produce color separations. The saved file consists of a four-plated cyan, magenta, yellow, black (CMYK) image plus a master (or V.2) file and a thumbnail of the image for viewing purposes.

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 are linked to the document using OPI software. This is done so that the application does not have to transmit these files during printing. The application sends the path information, identifying the location of the files and then they are sent directly from the server for printing. Keep in mind that DCS files are pre-separated before document creation begins. When job parameters such as the type of press to be used, are changed, it may be necessary to separate the image again.

Once the low-resolution FPO image has been placed in the document, and the document has been sent to print, CorelDRAW will send the color separations instead of the FPO image. The imagesetter produces full color separations which are sent to be printed. OPI systems that support DCS store the color separation files on a central server so that the application does not have to transmit these large files during the printing process. The application sends the path information to the separation files, and these files are sent from the server to replace the FPO image.

CorelDRAW Graphics Suite 12 and OPI software such as Colorcentral or Helios Ethershare 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 substituted in a print time acting independently of the application and the document containing the low-resolution EPS file.

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Selecting an OPI System

If you plan to use OPI or purchase a system for your service bureau there are several factors to consider, including the following:

supported file formats
Some supported file formats include: Scitex .CT, RGB .TIF, CMYK .TIF, .DCS, four-color .EPS, Photo .YCC & .PICT.

clipping paths
Ensure that the server can correctly handle any clipping paths that have been applied to the image.

color management
Some OPI systems use color management so that the FPO images have the same color characteristics as the final output. This can save time and money at the printing press and can reduce the number of proofs that must be printed.

image manipulation
Does the OPI system handle changes that have been made to the work? Can it properly support rotation, skewing, resizing and objects being inserted on top of images? Ensure that the system provides the required support in these areas.

using low-resolution FPO files
Some OPI systems allow a variety of resolution, line-screen and format options for the FPO image to provide optimal output when outputting to your in-house color printer. Ensure that the low-resolution images will be compatible with the system and work habits with which they will be used.

cross-platform compatibility
Confirm that the OPI system can recognize files created on various platforms.

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OPI Statements

A set of OPI statements will replace each embedded image within a document when the file is sent to print. The OPI statements specify the name and position of each image, as well as path information linking the low-resolution image to the high-resolution one that resides on the server. Additional information contained in the OPI statement can describe cropping, rotation and color specifications as well as image placement and manipulation information.

The following is a sample OPI statment:

%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

%ALDImageFileName: [filename]
Required Statement

• Records the name and path of the image (TIFF file) as it was imported into CorelDRAW.
• Embedded spaces and other Windows naming conventions are supported without requiring parentheses around the string.
• The statement line including path and filename cannot exceed 255 characters.

%ALDImageID: [filename]
Optional Statement

• An identifying string used by the OPI server to identify the high-resolution image residing on the server.
• This information is stored in the TIFF file as part of a reduced-resolution image, as Tag# 32781 (0x800D).
• TIFF data type is ASCII.
• This statement may be used in conjunction with the %ALDImageFileName statement to point to the high-resolution 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 DCS "%%+" convention.

%ALDImageDimensions: [pixelswide] [pixelshigh]
Required Statement

• Image dimensions of the embedded image are described in pixels.
• This statement is used in conjunction with the %ALDImageCropRect statement to relay image cropping information to the OPI server.

%ALDImageCropRect: [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 provided 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 with left and top being the upper left corner of the upper left pixel of the cropping rectangle, and right and 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.
• The height of the cropped area is the difference between the bottom and top coordinates of the cropped area.

%ALDImageCropFixed: [left] [top] [right] [bottom]
Optional Statement

• This statement provides the same information as the %ALDImageCropRect statement but 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.

%ALDImagePosition: LLx, LLy, ULx, ULy, URx, URy, LRx, LRy
Required Statement

• Describes the location of the 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.

%ALDImageResolution: [horizRes] [vertRes]
Optional Statement

• Resolution values are provided 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.

%ALDImageColorType: Spot Process Separation*
Optional Statement for Grayscale Images

• %ALDImageColorType gives the type of color specified by %ALDImageColor.
• Separation indicates that the image will be printed on all plates and usually corresponds to the registration color specified in the color palette of the application.
• If the %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.

%ALDImageColor: [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 blank or special characters are part of the colorname.
• The grayscale image will be printed using shades of the %ALDImageColor value; if the specified color is Process Blue with a CMYK value of 1 1 0 0 , the black pixels in the grayscale image will be printed full blue (1 1 0 0), the 50% gray pixels will print a 50% tint of blue. White pixels will not be printed.
• The default is 0 0 0 1 (Black)

%ALDImageTint: 0 | 1*
Optional Statement for Grayscale Bitmaps Only. Default is 1

• Describes the percentage of color to be applied to the image in a value between 0 (no ink) and 1 (solid).
• Values 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.

%ALDImageOverprint: False | True*
Optional Statement for Grayscale Images. Default is False

• When set to false, the image will knockout underlying objects on the separations.

%ALDImageGrayMap: [value]*
Optional Statement for Grayscale Images

• Matches color mapping within the application and records changes made to the brightness and contrast of the image.
• The application lookup table provides intensity values for each possible pixel value, starting with pixel value 0 (black) through 65025 (white).

%ALDImageTransparency: false | true*
Optional Statement. 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.

%ALDImageAsciiTag: [TIFF tag number]
Optional Statement

• This statement relays TIFF ASCII tag values to the OPI server.

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Working With Linked Bitmaps

CorelDRAW 12 allows the linking of bitmaps stored elsewhere on the hard drive without using OPI software. Bitmaps can be linked by enabling the Link Bitmap Externally option when importing them into a CorelDRAW document. This feature allows for the addition of bitmaps into a document without greatly increasing the file size as is common when importing bitmaps directly. The bitmap that appears in the document when linked is a thumbnail representation of the image that resides on the hard drive.

To link a bitmap externally to a document:

1. Click File | Import.
2. Choose the drive and folder where the bitmap to be linked is located.
3. Select the file.
4. Enable the check box labeled Link bitmap externally.
5. Click Import.
6. Place the image as you would when importing any other file.

To update a linked bitmap:

1. Select the bitmap with the Pick Tool.
2. Click Bitmaps | Update from Link.

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