# 3468- File Preparation for Professional Output This document contains information to ensure files created with Corel® graphics applications are output successfully at the service bureau. Selecting a Service Bureau Look for the "Corel® Approved Service Bureau" logo. A "CASB" can output Corel files in their native format. They will not require an Encapsulated PostScript® (EPS) or Print (PRN) file. Their experience using Corel graphics applications enables them to open files in their Corel graphics software for pre-output checking in order to output files efficiently and cost-effectively. To find a Corel Approved Service Bureau Click on the Windows Start button, choose Programs, CorelDRAW™, Setup and Notes, Corel Approved Partners, and browse to the geographical location. For non-Corel Approved Service Bureaus, provide an EPS or PRN files. Proofing the Work It is important that work be proofed before it is printed. Proofs can be created from a desktop printer that allow checking for PostScript® and text problems. Color desktop printers can be used to preview color, but the accuracy of color reproduction in desktop proofs is usually low. Special proofing devices designed to simulate how a print job will appear can also be used. The proofs produced by these devices are called offpress proofs because they use color separations to produce proofs, but they do not use the printing press. Off-press proofs provide a closer match to the final press output, but are more expensive and take longer to produce than desktop proofs If accuracy and precision are critical, use printing plates created by the service bureau to create proofs. These types of proofs are the most accurate and expensive type. The proofs are often used as a contract between the client and the service bureau. Find what the service bureau guarantees when using a set of proofs as contract proofs. Scanning and Bitmap Considerations Understanding Optical Resolution and Interpolated Resolution Input quality is largely determined by a scanner's true or optical resolution. Optical resolution is the actual amount of data an imaging device is capable of sensing or sampling. To improve input resolution, some scanners use interpolation formulas that fill in pixels between the actual scanned pixels. Interpolation algorithms average the color or grayscale information between adjacent pixels, adding new pixels to increase the resolution. In general, images with an interpolated resolution appear softer than the original and don't produce satisfactory results if high-quality color reproductions are needed with broad tonal ranges and detail. Better results will be achieved using a scanner with a higher optical resolution scanner than with a scanner using interpolated data. Evaluating Source Images The quality of the source image is equally as important as the capabilities of the imaging device being used. By using an image editing application, a high quality image can be manipulated by varying the contrast and adjusting the light and the color balance. Dot Gain Considerations When the image is intended for output using a printing press, one of the most important considerations is the inevitability of dot gain (the spreading of ink on paper that will cause the image to appear darker). When evaluating whether to include a certain image, assess the willingness to accept the increased density (the degree of opacity) or if confident the dot gain can be compensated for using an image editor after the image is scanned. Consult the Service Bureau if they have special dot gain requirements for the job. Avoiding Physical Imperfections in the Original Physical imperfections such as dust, scratches, fingerprints, and other debris become magnified when an image is scanned. Clean the scanning surface and remove any flaws in the image before scanning otherwise considering using a different image. Determine if any imperfections can be corrected in an image editing program. Avoid Resampling Because scanning affects the clarity and crispness of the final product, scan the images at a size that is as close to the output size as possible to avoid resampling. Resampling changes the resolution or size of an image to alter the number of pixels it contains. Downsampling reduces the resolution, decreasing the number of pixels in the image; upsampling increases the resolution, increasing the number of pixels in the image. Downsampling is generally a good idea for reducing any amount of unused information in an image. If displayed or printed at a higher resolution, the image will appear jaggy unlike the downsampled lower resolution. Upsampling consistently results in a lower input quality because interpolation algorithms add extra pixels to the actual sampled data to approximate detail. Resample an image only once because any degradation that results with the initial resampling becomes worse with subsequent resampling. Choosing an Appropriate Input Resolution Using the optimal input resolution ensures a sufficient amount of detail is reflected in the original. The image will not contain enough detail if scanned at too low a resolution. If scanning at a higher resolution than necessary, the result will be additional cost at the output stage, without a gain in image quality. Since many service bureaus charge by the hour, large files can substantially impact the final cost. The following are some general guidelines for choosing the right resolution for the print publishing project: 1. Don't scan at a resolution that's higher than the optical resolution of the scanner if the intention is to reproduce the image as close to the original as possible. Doing so causes interpolation algorithms to average pixels and add them to the sampled pixels, often producing unsatisfactory results. 2. Scan at an integral scanning resolution — a resolution that is evenly divisible into the maximum optical resolution of the scanner. An example is choosing an input resolution of 300 ppi if the optical resolution of the scanner is 600 ppi. Scanning by a value that's not evenly divisible causes the scanner to recalculate the value of every pixel and may change pixel values noticeably. Scanning at an integral resolution, by contrast, causes the scanner to use the actual sampled pixels 3. Choose an integral enlargement factor — a percentage of the original (e.g., 100%, 200%, etc.) up to the maximum optical resolution of the imaging device. In addition to these general rules, account for the following factors: dimensions of the original and the intended output size. Using the dimensions of the original and the output size, calculate the enlargement factor or reduction factor to use during scanning. 4. Enlargement Factor = Output dimensions / Original dimensions If Working with Grayscale or Continuous Tone Color Images If the image is grayscale or continuous tone and a halftone printer is in use, use the following formula to calculate the scanning resolution: Scanning resolution = Enlargement factor x (2.0 x Halftone screen frequency) The following is an example: the original image is 4 inches x 4 inches, the intended output dimensions are 2 inches x 2 inches, the halftone screen frequency is 85 lpi. The enlargement factor is 0.5 (2/4). The scanning resolution is 85.0 ppi (0.5 x 2.0 x 85). Convert this value to an integral enlargement factor of the scanner's optical resolution. For example, if the optical resolution of the scanner is 600 ppi, use the value 75.0 ppi or 100 ppi as the scanning resolution. If Working with Line Art Because of the nature of line art, both scanning and printing may be tricky. If the line art image has fine lines and edges, pixels may not properly align. To avoid jaggy edges and misalignment, scan the original at a high resolution — up to the optical resolution of the scanner. The Smart Way to Work with Bitmaps Another factor affecting PostScript file size is the way bitmaps are handled. If bitmaps are scanned at unnecessarily high resolutions, the final file size will be much higher than necessary. It is important to scale bitmaps before using them in CorelDRAW or another desktop publishing (DTP) application. If reducing the size of a bitmap in a DTP package, the file size does not decrease. Resample the image in a photo editing application such as Corel PHOTO-PAINT™ before placing the bitmap. Use a photo editing package to crop bitmaps. Most DTP packages crop bitmaps by covering the portion of the bitmap that is cropped. As with scaled bitmaps, the file size is not reduced. One notable exception to this rule is CorelDRAW 7 & 8, which only includes the portion of a bitmap that is visible in a PostScript file. Vector Image Considerations Reducing the Complexity of Vector Images Vector images are composed of lines and curves called paths. If the paths that make up a vector image are very complex, the RIP will have trouble rasterizing the publication. This problem is most apparent when using PostScript Level 1, but PostScript Level 2 is still prone to problems caused by complex vector images. The complexity of vector objects can be reduced by breaking them into smaller objects. Several PostScript settings can be changed that are designed to reduce the complexity of vector images. For example, the number of segments can be changed that PostScript uses to draw curves by increasing the flatness setting. In Corel applications, these settings are found within the printing options. Keeping the File Tidy When preparing a publication, do not clutter the file with material that adds nothing to the publication. Any extra information increases the PostScript file size and causes problems when producing film. Unnecessary elements increase the time it takes for the RIP to produce the film, or might even cause the RIP to fail entirely. If the print job occupies excessive imagesetter resources because of unnecessary information, expect the print job to take longer and cost more. Out of Sight, Out of Mind A common cause of extremely large PostScript files is hidden objects. An object becomes hidden when it is inadvertently placed behind another object and then forgotten. If a small part of an object is supposed to show, do not cover large portions of it with a white box or with other objects; edit the object to include only the desired object. Overloading a File with Fonts If the publication uses a large number of fonts, the imagesetter may be unable to reproduce the work. To avoid this problem, either reduce the number of fonts in the publication, or convert some of the text to curves. Converting text to curves works best on larger type such as headlines or text in logos. Remember, if any text in the publication uses a font, that font is required when imagesetting. Even an extra space that is formatted incorrectly can add a font to the publication. Sending Work to the Service Bureau Transferring the publication from the computer to the service bureau can be difficult if the publication consists of one or more very large files. To send the work to the service bureau, use either a modem or a portable storage medium with a large capacity. Consider the following when choosing the medium: storage capacity, storage and retrieval speed, compatibility with the service bureau's system, and equipment required to store the files Another way to make the file transfer easier is to use some sort of file compression. Some applications, such as CorelDRAW, allow use of JPEG compression to reduce the size of the bitmaps in the publication. Examine the bitmaps on the proofs because JPEG compression can reduce image quality. File compression can also be used that doesn't degrade quality, such as WinZip™. The service bureau will have to decompress the files when they receive them. Make sure that the service bureau has the software required to decompress the files and that they are willing to use it. Including Vital Information When sending files to the service bureau include the following information: - paper size and orientation - number of pages - the application used to produce the publication - the colors used (e.g., process color, specific spot colors) - the fonts used, including the font technology (TrueType® or PS Type 1), the exact names of the fonts, manufacturers, and version numbers, if possible a list of all the files required to produce the publication - Include laser-printed separations of the job to make sure it separates properly. - Send only those files that are necessary to output the job - Include the phone number(s) to be reached at. - Call the Service Bureau before picking up the job in case there are last minute delays. - Fill out the Service Bureau work order completely and cross out any fields that don't apply. Use a highlighter pen to point out special instructions. - Do not include blank pages or pages not intended for printing with the file. - Simplify the files to avoid output problems. The most difficult features to output are clipping paths, masks, high-resolution raster images, patterns, blends, complex fills etc. - Break up large files into smaller ones so as not to exceed the memory limits of the imagesetter. - Remove unnecessary elements and objects outside the page area . Choosing the Best File Format There are two basic file formats that can be used to send the publication to the service bureau: the PostScript file format or the file format of the application in which the publication was created To send the service bureau a PostScript file (.PRN extension), print the publication to file and send them the .PRN file. Ensure that the correct printer driver is in use when printing to file. Use the imagesetter's printer driver as the default driver when laying out the publication. Different printer drivers can change the way a publication looks, especially text flow. If sending a .PRN file, the service bureau does not need to have the software used to create the publication. The service bureau does not need the exact fonts that were used, as long as the PRN file was set up to include the fonts. The disadvantage of sending a .PRN file is that the responsibility of error free imaging lies with the user. The service bureau cannot fix problems with a .PRN file. If the service bureau is willing to accept the file format of the application in which the publication was created, then sending the publication in that format allows the service bureau to adjust the prepress settings and correct any errors. The final choice depends largely on the capabilities of the service bureau, the user's ability to properly set prepress options, and the degree to which the service bureau is trusted. Talk to the service bureau, weigh the pros and cons of each file format, and choose the best option. Linked files When using images in a publication, a link can be created between the image file and the DTP file rather than embedding the image in the DTP file. Linking files makes it easier to transfer the publication to the service bureau because of dealing with several smaller files rather than one large file. If using linked files, include all the files when sending the publication to the service bureau. As long as the service bureau has the linked files, all of the links can be resolved, but missing files may cause unnecessary delays. If using Open Prepress Interface (OPI) to place images in the publication, ensure the publication is set up so that the low-resolution image place-holder is replaced by the high-resolution image. Managing Fonts A font consists of two parts: a screen font and a printer font. The screen font is displayed in the DTP application; the printer font is used by the RIP to create the raster image of the publication. Two types of font technology are in wide use: TrueType and PostScript Type 1. Some publishing professionals favor Type 1 fonts because they have a reputation for looking better than TrueType fonts. Third-party software is required to use Type 1 fonts, whereas TrueType font management is built into Windows. Make sure the service bureau knows which fonts are being used. Avoiding Problems with Fonts Tell the service bureau which fonts are used. For example, two fonts with the same name that are made by different manufacturers are different. Results may differ when using TrueType fonts but the service bureau uses Type 1 fonts. Even a slight difference can alter the text flow in the publication. The most obvious font problem is a missing font. If a font is unavailable, PostScript will replace that font with Courier (this is Courier). If applying styles to fonts, such as bold or italic, make sure the proper typeface is being used for that style. There are specific typefaces for each available style, but if the typeface is not installed properly, some applications simulate the style by altering the normal typeface. In some cases, the PostScript interpreter will ignore the simulated styles and the text will look normal.