HP Large Format Color Copiers Color Accuracy in a proofing workflow Color reproduction for the HP Large Format Color Copier products family Please download the latest PANTONE tables from the technical support section of: http://www.designjet.hp.com Notes about the document The settings and examples described in this document apply to the HP Large Format Color Copier products family using the latest version of HP Designjet Scan software available at the time of document development.
Contents 1. INTRODUCTION TO THE DOCUMENT......................................................................... 4 2. COLOR COPYING GUIDELINES ..................................................................................... 5 2.1 CHECKPOINTS BEFORE STARTING A JOB .............................................................................. 5 2.1.1 Scanner ....................................................................................................................... 5 2.1.2 Printer ...........
.4.5 Black enhancement ................................................................................................... 48 3.4.6 Background cleaning ................................................................................................ 48 3.4.7 Sharpen ..................................................................................................................... 49 3.4.8 Blur .................................................................................................................
1. INTRODUCTION TO THE DOCUMENT The aim of this document is to provide customers with a simple guide to getting good color reproduction when using the HP Large Format Color Copier products. By making the process of scanning and printing easier to understand, we believe users will be able to achieve the desired color reproduction results.
2. COLOR COPYING GUIDELINES The HP Large Format Color Copiers allow an original image to be reproduced using a scanner, a printer and a controller (called touch screen). The reproduction can be done: • • In one step (a Copy process) In two steps (a Scan process followed by a Print process) with an intermediate saving of the digitized data into a file In this document, we will not differentiate between the two cases: we will describe the Scan process and the Print process separately.
Has the scanner been on for more than 1 hour? If not, the colors may vary during the scan. Does the scanner need to run the scanner maintenance process? If so, follow the scanner maintenance manual. If unsure, see section 3.1.2.2 of the Annex. Typically, the scanner maintenance process should be run every 100 scans or once a month, but it depends very much on the type of originals you are scanning.
2.1.3 Touch screen Do you have a media profile adapted to the media currently loaded into the printer? If not or not known, please create a media profile as described in your scanning system’s documentation. If it is not correct, the output image may have serious defects: too much ink (dark images, smearing, bleeding), too little ink (washed out, low contrast images), wrong colors. 2.
settings) Sepia background (Sepia; CAD with advanced settings) Other ….. Document: mixed text (or lines) and pictures (CAD Mix; Brochure) Map (solid areas and lines) (Map; Map) 1.3 Definition of own type of original: Do you need some extra color management or image enhancement applied to the image? If unsure refer to sections 3.4 and 3.5 of the Annex.
2. Printing options 2.1 2.2 2.3 What is the currently-installed printer name in the touch screen? ………………………….. Which media profile are you going to use? (For information see section 0 in the Annex) ………………………….. Which print quality do you need? Best gives higher quality but slower throughput; Fast gives higher throughput but lower quality. It is recommended to select Fast for drafts, Normal for non-critical tasks and Best for final presentations. Best Normal Fast 2.
2.3 Running a job: operator settings The third step of the process, after having got through the checkpoints in section 2.1 and answered the questions in section 2.2, is to configure the touch screen. Firstly, you should choose the tab corresponding to the action you are about to perform: • Scan: scan the original and save the digitized image to a file on CD, hard disk, flexible disk or networked disk. This file may be printed later. We will call this option Scan to File.
The settings selected in section 2.2 are herein referred to by their line number appearing in parentheses (e.g. (1.1) when setting the Color mode). 2.3.1 Scanning Scanning is the digitization of the original image. It happens either when we are Copying or Scanning to File (i.e. Copy or Scan tabs). Special attention should be paid to this process where, besides the digitization, most of the image enhancement and part of the color management take place.
2.3.1.1 Type of original (1.2) Since there are many settings which are used for image enhancement and color management, templates (or groups of settings) are provided through the type of original setting in order to ease this task. It consists of the definition of archetypes of different originals to which specific settings’ values have been associated.
• B&W scanning o Photo o Map o CAD Mix o CAD Lines o Blueprint o Sepia In most cases, choosing the correct “type of original”, as specified in point 1.2 in section 2.2, is enough to obtain a good scan and, subsequently, a good print. A description of when each type of original should be used is provided in the following tables. Color Mode Photo Should be used when copying color pictorial images, characterized by having many colors, transitions between colors or shadings.
Brochure Should be used when there is a mix of text (sharp and crisp contrast) and pictures. It is a compromise between having good perceptual reproduction of the pictures and crisp text. Map Should be used for maps, graphics and other documents that have area fills: areas of one color surrounded by areas of another color. The edges between adjacent color areas are enhanced (sharpened) and, assuming that the background is white, a background cleaning feature is applied.
Black and White Mode Photo Should be used for pictorial images that have many shades of gray. In principle, this is equivalent to the (Color) Photo type. Map Should be used for maps, graphics and other documents that have area fills: areas of one shade of gray surrounded by areas of another shade. The edges between adjacent gray areas are enhanced (sharpened) and, assuming that the background is white, a background cleaning feature is applied.
Blueprint Should be used when the original has very similar bluish background and foreground. If you selected Photo for this type of original the output would be very noisy and it would be hard to distinguish the lines. This “type of original” setting includes a process to clean the background in order to make the output clearer. Sepia This option uses the same principles as Blueprint but it is designed for sepia color backgrounds.
If the image contains fine details (CAD drawings, fine art, maps), you may consider scanning at a higher resolution. 2.3.2 Printing Printing is the materialization of the image and can be performed whether you are in the Copy or Print tabs of the touch screen. Please remember that, besides the formatting required to send the image to the printer, most of the color management takes place in this phase. With regard to color management you should define: • • • • Which printer will be used (2.
2.3.2.2 Print quality (2.3) The Print quality, Ink printer original, Black Ink only, Optimize for drawing and Max detail settings are specified under the Settings button in the Copy or Print tab. Note: The list of options depends on the printer installed. Not all settings are available in all printer models. To get the best possible image quality and in order not to lose any of the reproducible colors, you should choose Best print quality together with a good media such as Photo Gloss.
2.4 Post-job recommendations and Troubleshooting 2.4.1 Post-job recommendations Handle the copy with care, letting it dry completely. It is recommended not to expose it to direct sunlight (or any other source of UV rays) or other extreme conditions (humidity, temperature). If appropriate, it is recommendable to laminate it in order to avoid scratches and to increase its “light-fastness” (durability of colors).
2.4.2.1 The colors of the copy are very different from the original 1.a There is an overall color cast 1 Are you viewing the copy in the expected viewing conditions? No Try viewing it with the correct light and environment. No Reselect the Media type in the printer or scanner, and try again. Yes 2 Is the Media properly specified in the printer front panel? Yes 3 Is it a new Media type? Needs a new Media Profile to be created? Yes Create a new Media Profile.
1.b Most of the colors are OK but certain ones are very different Follow the steps 1 to 5 as in 1.a and proceed from there: Are some of the colors non-reproducible? See section 3.2 in the Annex Yes System Limitation. Try modifying saturation and/or lightness No Contact HP Support Organization 2.4.2.2 Grays are wrong in a color copied image Follow steps 1 to 4 as in 1.a There is an overall color cast in section 2.4.2.1.
To avoid copying the background of a background-colored document (typically sepia) you should use the background cleaning option when scanning in color mode; if you are interested in B&W copying you should use either Sepia or Blueprint type of original. 2.4.2.6 Vertical bands appear in the copy This normally happens when the glass plate is dirty (either because it was dirty before the scanning or because the original left tiny bits of coating as it moved over it).
3. ANNEX 3.1 Color reproduction: theory of operation The following is a theoretical treatment of the technology involved in the scanning and reproduction of images. The technology at work in your particular product may be slightly different from that referred to the description that follows. Color reproduction consists of transferring an original image that resides on a substrate onto another substrate (paper or other media), as accurately as possible.
The principle behind color reproduction is that the original and the final image relate to each other according to the desired reproduction intent. It is also important to underline that the process includes image enhancement. This feature is included so that when the original is noisy, badly contrasted or imperfect, the resulting output can be enhanced (smoother, better contrasted, with enhanced edges and lines).
• According to the shadows or contrast levels: o two levels: only black and white (e.g. text document) o multilevel: many gray levels (e.g. picture) • According to the original’s conditions: o Clean image o Damaged or noisy original: Stained, marked, smudged, spotted, … Scratched, torn, … It is important to know what type of original you are handling in order to use the correct reproduction settings.
3.1.2 Large format scanner The scanner is the device that digitizes the original and sends it to the processor for further digital treatment. It consists of a light source, a paper movement mechanism, RGB image sensors (two or more cameras) and the electronics required to process the data from the sensors. 26/55 Color Reproduction for the HP Large Format Color Copier products family.
3.1.2.1 Light source The light source provides enough light along the vision strip so that, after being modified by the original image2, there is sufficient reflected light to reach the image sensors. The light source (lamp) stabilizes after the scanner has been on for approximately one hour. Therefore, if the color reproduction is critical and you don’t want to see differences from one end of the copy to the other, it is advisable to start scanning one hour after powering on the scanner. 3.1.2.
The cameras must be periodically calibrated in order to avoid undesired geometrical distortions in the final copy, as well as ensure a correct color capture. Calibration can be performed using the scanner maintenance tool provided with the system. It is advisable to run the scanner calibration every time the system warns the user to do so, or when any of the following defects appear: jagged lines, blurry images, modified colors (with respect to previous copies). 3.1.2.
3.1.3 Touch screen The touch screen provides the user interface to the system and connects the various elements of the system.
3.1.4 Large format printer The task of the printer is to place tiny drops of ink on the media (paper or other substrate) in order to form an image that corresponds to the data file received. Desired pixel color Printheads Ink drops Printed image Input image Your HP Large Format Copier supports the printers defined in the product’s data sheet. Most of them are thermal inkjet printers, which means that little drops of ink are heated up to the boiling point and sent to the media.
The HP Large Format printers have a way to compensate for these problems: ClosedLoop Color calibration (CLC). This process consists of calibrating the printer by applying a color value table, which is created by printing a color ramp for each ink and measuring it with an internal color sensor. Depending on the printer model, there are different ways to access this feature (see your printer’s documentation).
The media profiles define the relationship between the colors the scanning system sees and the colors the printer is able to print. For some printers there is a set of pre-installed media profiles (High-gloss Photo, Coated, Bright White, etc.). However, if you need to print on other media, or desire a color reproduction system that better matches your media, it is advisable to create new media profiles, as specified in section 0.
Image enhancement is used to improve the original image or a portion of it. The final image will not be an exact copy of the original but, rather, a re-interpretation of it that corrects some of the original’s shortcomings (e.g. stains, fuzziness). There are two types of image enhancement available in the touch screen: • • Blur: smoothes the image. It is used, for example, when the original is worn out and has spikes or stains that you don’t want appearing in the copy. Sharpen: enhances edges in the image.
3.2 Which colors can be reproduced? The colors that can be reproduced vary between different printers and different printing media. At HP, we analyzed various environments and reached the following conclusions: • • • Glossy paper (such as HP Universal High-gloss Photo Paper) has a much wider “gamut” (amount of reproducible colors) than matte paper, such as HP Heavyweight Coated Paper.
HP Designjet 500/800 with HP Universal High-gloss Photo Paper (Q1427A) HP Designjet 500/800 with HP Heavyweight Coated Paper (C6030C) Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet 105x with HP Universal High-gloss Photo Paper (Q1427A) HP Designjet 105x with HP Heavyweight Coated Paper (C6030C) 36/55 Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet 4500 series with HP Universal High-gloss Photo Paper (Q1427A) HP Designjet 4500 series with HP Heavyweight Coated Paper Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet 5500 with HP Universal High-gloss Photo Paper (Q1427A) HP Designjet 5500 with HP Heavyweight Coated Paper (C6030C) 38/55 Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet T1200 with HP Universal High-gloss Photo Paper HP Designjet T1200 with HP Heavyweight Coated Paper Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet Z2100/Z6100 with HP Universal High-gloss Photo Paper HP Designjet Z2100/Z6100 with HP Heavyweight Coated Paper 40/55 Color Reproduction for the HP Large Format Color Copier products family.
HP Designjet Z3200 with HP Universal High-gloss Photo Paper HP Designjet Z3200 with HP Heavyweight Coated Paper Color Reproduction for the HP Large Format Color Copier products family.
3.3 Guidelines to create or validate a media profile Many of the color problems appearing in the HP Large Format Color Copiers products are related to the mismatch between the media’s color characteristics set up in the touch screen and those of the real media that is loaded into the printer. If there is such a mismatch, colors may be reproduced incorrectly, grays may have some color cast or some colors may be lost.
3.4 Effects of changing default media profile settings (color) This section describes how the media profile settings act upon the image. To create or modify5 a type of original you need to select an existing one (Photo in this example) and press the Tool button . In the preview pane you will see two copies of the image: the bottom one is the original and the top one is the image modified by the settings of the selected type of original.
3.4.1 Method Method defines the basic image enhancement to apply to the scanned image. It depends on the printer installed, but may have one of the following values: Continuous tone: used when the image has many colors and transitions among them. This method is used in the “Color Photo” type of original. Graphics: used for images where lines and edges should be sharp. Used in “Map” and “CAD” types of original. Mixed: used when the original contains both text and pictures.
Saturation - 6 Saturation 0 Saturation + 6 3.4.4 Color balance This setting is used to adjust the color balance for the whole image. If you find that the overall image has a color cast (e.g. it is too green) then you may correct it by modifying the color balance. You may set the Color balance value to RGB (Red, Green and Blue) or CMY (Cyan, Magenta and Yellow), depending on the selection made in the “Setup tab > Options button > General button > Color Balance”.
effect as decreasing (or increasing) the values of the two remaining colors of the same set. For example, to make the image bluer you may increase the Blue value or decrease both the Red and Green values. The entity of the color change differs depending on the direction you are heading. In other words, when moving towards positive values in RGB mode the appearance of the image changes slightly, whilst when moving towards negative values, the image exhibits a much bigger change.
The following picture shows the effects of increasing the RGB values of an image: +R +G +G +R +R +B +G +B +B Color Reproduction for the HP Large Format Color Copier products family.
3.4.5 Black enhancement This setting is used to blacken all areas below the defined lightness level. It is employed to enhance the text parts of a document, when black text is copied as gray. Valid values range from 0 to 255. If 0 is selected, the image is not modified; if 255 is selected the whole image will be black. 3.4.6 Background cleaning This setting is used to whiten all areas above the defined lightness level. Valid values range from 0 to 255.
3.4.7 Sharpen This setting is used to sharpen the image. It enhances the edges between areas of different colors, thus resulting in better-defined text and edges. The strength of the sharpening is controlled by its value. 3.4.8 Blur This setting is used to smooth the image. It is useful when the scanned original is “noisy” (i.e. color disturbance, graininess and non-area uniformity). Color Reproduction for the HP Large Format Color Copier products family.
Although blurring is the opposite of sharpening, they do not cancel each other out. In fact, the two options can be usefully combined to blur away noise in the image first and then sharpen the result. Observe below the same example as before, with blur and sharpening applied. Note that now there is no “augmented noise” in the text area, compared with the result when only sharpening was applied. 3.
3.5.1 Method Method defines the basic image enhancement to apply to the scanned image. It depends on the printer installed, but may have one of the following values: Graytone: used for pictorial images (pictures with many gray shades). B&W Threshold: used for pure B&W clear CAD drawings and/or text only documents, where the background is pure white and the text or lines are well defined.
3.5.3 Sharpen This setting is used to sharpen the image; it enhances the edges between areas of different colors (see the explanation in section 3.4.7). 3.5.4 Blur This setting is used to smooth the image. It is useful when the scanned original is “noisy” (see the explanation in section 3.4.8). All comments made in section 3.4.8 regarding the combined use of sharpening and blurring apply here as well. 52/55 Color Reproduction for the HP Large Format Color Copier products family.
4. GLOSSARY Background cleaning Black enhancement Black ink only Blueprint Blur CAD drawing Color balance Color calibration (CLC) Color management Copying Enhance gray Gray balance ramp Hue Image enhancement Inkjet printer Lightness Image enhancement feature that whitens all areas above a defined lightness level. Typically used to avoid noise, stains or wear marks. Image enhancement feature that blackens all areas below a defined lightness level. Typically used to enhance text.
LUT file Media Media profile Non-reproducible color Original Printhead alignment Printing Saturation Scan resolution Scanning Sharpen Stitching Touch screen Type of original 54/55 It distinguishes light from dark areas. A Look-Up Table (LUT) file. It correlates n-dimensional entries with m-dimensional outputs. In this instance, it correlates a 1-dimensional entry (the lightness) with a 3dimensional output (the corresponding Red, Green and Blue values).
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