216 colors (Web Safe) |
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See Web-safe colors | ||||||||||||||||
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256 colors |
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When a computer?s graphics system uses 8 bits of information to store each pixel in an image, the most effective way of gaining the widest range of colors is to use a Color Look Up Table (CLUT). This is called indexed color. Each pixel can be one of 256 colors (2^8) and the colors are chosen from a palette of 16 million. If the palette is chosen carefully and the image doesn?t have too wide a range of color, you can get a reasonably pleasing result. The choice of pallete, and what your operating system does to it, however can really mess up your images. Both the Mac OS and Windows have standard 256-color palettes (not that same colors of course). They are called the system palettes and were chosen to have the widest application possible. Photoshop can create custom palettes for your images but beware that the system displaying your image may not have access to the custom palette. | ||||||||||
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4-color |
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A press, press run or printer that applies 4 colors to the paper. For process color the 4 colors are CMYK (Cyan, Magenta, Yellow, and Black). | |||||||||||||
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5000K |
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5000K has the coordinates for xyY of (0.3457, 0.3585, 100) See white point |
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6500K |
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see white point | |||||||||||||
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9300K |
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see white point | ||||||||||
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a |
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a is the axis in the Lab color space which denotes the ?red-green? component of the image. One end of the axis is green and the other end red. Combined with the b axis, you can describe the hue and saturation of a color. | ||||||||||
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Additive Primary Colors |
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Red, Green and Blue are additive primary colors. That is, in an imaging system which creates colors by using light (monitors, file recorders), red green and blue can combine in equal quantities to produce white. All the colors the device is able to create (the device?s gamut) are produced by varying the amounts of red, green and blue. | |||||||
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Antialiasing |
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Antialiasing is a technique used to smooth the edges of line art, fonts, and other vector art by blending the edges of the object with its background and creating intermediary colors and shades. Technically it lowers the resolution of the image but done correctly, and viewed from sufficient distance, can appear to smooth previously jagged edges and actually increase the apparent resolution. It is a good technique for screen display (CD-ROM and Web publishing) but should not be used for printing in most cases as the higher resolution of a printing device will often reduce jaggies and antialiasing would make it look worse. | |||||||
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b |
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b is the axis in the Lab color space which denotes the ?blue-yellow? component of the image. One end of the axis is blue and the other end yellow. Combined with the a axis, you can describe the hue and saturation of a color. | ||||||||||
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Bit depth |
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The number of bits which are used to store each pixel in an image. Each additional bit adds twice as many color combinations to the number available. 1 bit (bit-mapped - monochrome), 8bit (indexed color and web-safe color), 16 bit (?thousands of colors?) and 24 bit (?true color?, ?millions of colors?) are common bit depths. Increasing the bit depth can greatly affect the quality and size of your images. |
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Bitmap |
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A raster computer image which is monochrome. Each dot can either be on or off and there are no shades or colors available. It is called a bit map because the bits used to store the image map directly to the dots on the screen 1 to 1. | |||||||
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Blackbody, Black Body Radiation |
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A black body is a theoretical object which absorbs all light which strikes it and emits different wavelengths of light depending on the temperature to which it is heated. The color temperatures of 5000 degrees K, 6500 degrees K, etc all refer to the ?color temperature? of a black body heated to that temperature. Kelvin degrees are similar to degrees Celsius but start 273 degrees lower at absolute zero (0 degrees Celsius - freezing - is 273 degrees Kelvin) | |||||||
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Brightness |
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1) Setting on Monitors - unlike contrast (which should be set to it?s maximum setting in most cases), brightness should be set manually according to your profile software?s instructions. As the phosphors in your monitor fade over time, the amount of light they emit will decrease and you will probably have to turn your brightness up. If you are unable to turn it up to an acceptable level it?s time for a new monitor - give yours to your favorite accountant - they?ll love the size and not care about the color. 2) B component in HSB - The visual attribute by which a color appears to exhibit more or less light. This correlates directly with the amplitude of the light waveform (as opposed to the purity or the wavelength(s)) |
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Calibrate, Calibration |
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Calibration is the act of returning a device to factory, or some other, known specification. It does not characterize the device in the way a Profile does, but calibration should always be performed prior to building a profile. Re-calibrating a device sometime after a profile was built should return the device to the state where the profile is valid and can continue to be used. |
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CCD |
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CCD stands for Charge Coupled Device. It is a light sensitive solid-state device that is used in digital cameras, most desktop scanners (and some higher-end ones), colorimeters, video cameras, and other devices. Their dynamic range is improving but is still not up to that of the PhotoMultiplier Tubes used in drum scanners. | |||||||||||||
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CIELab, Lab |
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CIELab is the color space that ICC Profiles and CMMs often use as an intermediary space when converting colors. So a monitor to printer match translates colors from the monitor*s space (RGB) into Lab and then into the printer*s color space (CMYK for example). The L component is the lightness of the color. CIELab, or more correctly CIEL*a*b* is a (mostly) device independent color-space based on the measurements of hundreds of humans the CIE made in 1931 when they created the CIEXYZ color space. In 1976 the CIE created the Lab space to reflect the entire gamut or range of colors the human eye can typically see. The Lab space, unlike other CIE color spaces, is supposed to be perceptually uniform. That is, any movement within the space, in any direction, should result in an equally perceptible color shift. There are many who believe that the Lab space is not perceptually uniform but that is outside the scope of this glossary. LCH is another way of measuring the same color space. (see LCH for more information) The Lab color space is not precisely device independant as it is defined relative to a reference white point. This white point is often based on the whitest point that can be generated by a device or a standard white point (like D50). |
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Chroma |
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Chroma is the C component of the LCH color space. Chroma represents how far out from the center of the color space (radially) a color lies. The farther out the more saturated the color. The "colorfulness" of a sample judged proportional to the brightness of a white reference sample in the same medium and under the same illumination. |
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Chromaticity Diagram |
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The Chromaticity Diagram is a horseshoe-shaped graph of the CIELab color space where the L component has been removed and the a and b components are then graphed in 2 dimensions. It is a very useful diagram for getting a quick feeling for not only the range of colors humans can perceive but the ranges of colors (gamuts) that different devices can (or cannot) display. | |||||||
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CIE - Commission Internationale De l'Eclairage |
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Link: http://www.cie.co.at/cie/
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CLUT |
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A CLUT is a Color Look Up Table. This is used with indexed color schemes when a lower number of bits are used to store each pixel's color so a look up table is used to increase the number of colors available. See Indexed Color for a more complete description. | |||||||
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CMM - Color Matching Method |
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The CMM is the "engine" that actually does the work of color management. There are many different CMM's available from vendors such as Linocolor, Kodak, Adobe (within Photoshop), and others. The CMM contains the actual executable code that uses the ICC Profile information supplied by the user to transform the colors of a document. While the debate may rage on about which CMM is best to use (and that probably differs the most depending on your workflow), one thing most color scientists would agree on is you should choose one CMM and use it throughout your workflow. At this time, in our opinion, this removes the Adobe CMM from most workflows as it is only available within Photoshop (and presumably more Adobe products as time goes on). Unless you do all your color work in one application, you should choose a CMM that is available to all applications. |
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CMYK Cyan, Magenta, Yellow, Black |
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The four colors commonly used in process color printing. Black is added to CMY to enhance the density of dark areas and solve gray balance problems encountered when trying to make neutral grays with CMY alone. The letters stand for: C: Cyan |
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Colorimeter |
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A device for measuring tri-stimulus values like RGB and XYZ. Colorimeters are often used for monitor calibration and profiling. They read their measurements using three or more filters, and as such are not as accurate as spectrophotometers at measuring the true color characteristics of objects. | |||||||
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ColorSync |
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ColorSync is Apple?s color management standard and framework which has been built into the Mac OS for years. ColorSync is a standard method for developers to call the operating system when they want their programs to correctly manage color. There are also provisions in ColorSync that allow developers to write their own Color Matching Methods and also for the users to select different ICC profiles to use. In some sense, ColorSync is the glue that holds it all together, but it is also a standard, one that ships with every copy of Mac OS. That reassures developers, and end users alike that it will be present in their users? systems and solutions can be built around it. |
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Colour |
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as in the correct spelling ;-) | |||||||
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Contrast |
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1) setting on monitors 2) in images |
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Cross-platform color |
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Cross platform color management refers to managing color between different operating systems. Getting your Mac and Wintel monitors to match and your printed output to be the same is a difficult task. Luckly, several things are in place to help, and others are on their way. - ICC Profiles - are platform-independent by definition. That means you can easily move them from machine to machine. Some things working against you are: - The gamma settings can be quite different between the Mac and PC. Photoshop can compensate for this when designing, but when displaying on different systems you can have problems. |
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Displays |
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see monitors | |||||||
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Drum scanners |
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see scanners | |||||||
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EMR |
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Electromagnetic Radiation. Visible light is one subset of a whole range of radiation called EMR. | |||||||
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File formats |
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Graphics information, when written to disk, can be stored in many different formats. Some formats include compression as an option, and others it is required. Many file types can store additional information along with the graphic. This includes ICC profiles, color palattes, comments, and specifications. | ||||||||||||||||
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Film |
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1) for printing 2) photographic for scanning 3) dynamic range of |
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Indexed Color |
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When a computer?s graphics system uses 8 bits of information to store each pixel in an image, the most effective way of gaining the widest range of colors is to use a Color Look Up Table (CLUT). This is called indexed color. Each pixel can be one of 256 colors (2^8) and the colors are chosen from a palette of 16 million. If the palette is chosen carefully and the image doesn?t have too wide a range of color, you can get a reasonably pleasing result. The choice of pallete, and what your operating system does to it, however can really mess up your images. Both the Mac OS and Windows have standard 256-color palettes (not that same colors of course). They are called the system palettes and were chosen to have the widest application possible. Photoshop can create custom palettes for your images but beware that the system displaying your image may not have access to the custom palette. | |||||||
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Ink |
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absorption - see dot gain Spot Color inks are opaque and Process Color inks are transparent. It also means that spot colors emulated on a 4-color proofing device are affected by the proofing stock much more than they will be on the final press output. Nasty! |
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L |
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The L component in Lab and HSL color spaces is the lightness of the color. | |||||||
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Luminance |
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Luminance is the brightness component of colors described in the Lab color space. Is often expressed in Candelas per square meter (cd/m^2) |
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Process color |
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Process color refers to the inks and process used when a wide range of colors are reproduced using a limited number of inks. CMYK is the most common process ink set. Cyan, Magenta, Yellow, and black(Key) inks are combined in varying amounts to produce a reasonably wide range of colors. This is much cheaper than using a different ink for every color required and in the case of continuous-tone images like photographs, makes printing in color possible. |
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Profile |
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A file containing the colorimetric description of an input or output device in terms useful to a color management system. | ||||||||||||||||
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Resolution |
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Resolution has at least two meanings. 1) The correct meaning, used by physicists, biologists, and the scientific world in general, refers to the number of objects within a certain defined physical space. So in the publishing world it usually refers to Dots Per Inch (dpi), Pixels per Inch (ppi) , Lines Per Inch (lpi) or some other similar measurement. 2) The incorrect but very heavily used meaning, which is the size of an image or display. To say a display's resolution is 640 pixels by 480 pixels is common, but not really correct. Now if you said it was showing those dimensions at 72dpi, then you'd be correct. Now what is the difference between dpi, ppi and lpi? Dots refer to spots of ink, toner, or some other colorant on a piece of paper. They are the smallest dot that can be applied by that device and are usually monochromatic (they are either there or not, you don't have shades to choose from). Pixels (which is short for "picture element") refers to spots which appear on monitor screens. They can be one of a multitude of shades. What's the difference? Well, a pixel (of many shades) cannot be represented by a dot (of one shade) on a printer. So the printer gathers a whole bunch of dots together into a "cell" and, by varying the number of dots applied in that cell, can simulate a number of shades. If you want to simulate more shades, you need more dots in each cell. The number of cells per inch is called lines per inch (lpi) and is obviously not as many as there are dots per inch. What this means is that if you want your printer to output a continuous-tone image, you are going to have far fewer lines per inch than the say 600 or 1200 dpi you to which you are accustomed. |
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RGB |
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Red, Green and Blue are additive primary colors. That is, in an imaging system which creates colors by using light (monitors, file recorders), red green and blue can combine in equal quantities to produce white. All the colors the device is able to create (the device?s gamut) are produced by varying the amounts of red, green and blue. | |||||||||||||
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sRGB |
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sRGB is a ?device independent? RGB space which was proposed and adopted by Microsoft and Hewlett Packard as a standard color space for ?the average user?. It is supposed to represent the gamut of the ?average user?s? monitor. Problems associated with this include: - There is no such thing as an average user - especially with the high-end displays used by graphics professionals sRGB is not all bad. The basic idea of converting images to sRGB which are headed to the web (and when the audience is the general public) makes sense. In many cases, supplying a large profile with each image does not make for a speedy web site. With sRGB, no profile is required and a properly tuned system on the user?s end will display the image correctly. The sRGB also has a gamma of 2.2. This can cause display issues on monitors set to other gammas (like Mac OS systems, which are often set @ 1.8) |
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Saturation |
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The colorfulness of a sample compared to its brightness, where colorfulness is defined as lack of white, gray or black components. | |||||||
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Spectrophotometer |
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A device for measuring luminous energy at many frequencies throughout the spectrum. Spectral data can usually be displayed in convenient units such as CMY density, L*a*b* or XYZ. | |||||||||||||
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Spot color |
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Spot color refers to colors in an image which are created with a specific ink formulation rather than a combination of inks like in process color. One of the more popular spot color ink sets is the Pantone Matching System. Pantone has created a series of inks which can be used with high reliability in a projects where you know you have additional plates available to you. (don't try to use spot colors in newspapers for instance, the chances of the press operator loading another plate just for your logo on page 27 is remote indeed) |
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Stock |
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The paper stock on which you print can have a major effect on your output. Stock comes in many forms and can range from newsprint all the way to plastic film. How inks are act when applied to paper is a complex issue and worthy of some discussion. There are several points worth considering: Spot Color inks are opaque and Process Color inks are transparent. Ink Absorption and Dot Gain |
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Subtractive primaries |
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Cyan, Magenta, and Yellow are subtractive primary colors. That is, in an imaging system which creates colors by using inks or other pigments (printers, presses, some proofing systems), cyan, magenta and yellow can combine in equal quantities to produce black (actually muddy brown in most cases - that's one of the reasons black is usually used). All the colors the device is able to create (the device?s gamut) are produced by varying the amounts of each ink color. Subtractive colors get their name because they are thought of as subtracting light out of an image. Cyan, for instance subtracts (absorbs) red light. If less red is required in a color, more cyan ink is added. |
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Tri-stimulus, Tristimulus |
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Values The quantities of red, green and blue lights of specific wavelengths and bandwidths needed to match a certain color. | ||||||||||
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UCR |
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Under Color Removal. The reduction of CMY percentages in dark pixels to limit the total ink printed in shadows. UCR is set by specifying a "Total Dot Percentage" (TDP) and "maximum black dot" from which UCR is calculated automatically. | ||||||||||
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Web browsers |
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Web browsers can affect the way color is viewed by your end user. Designed for speedy display, they aren't often optimized for image fidelity. Combine that with web designers who, understandably, squash images to their smallest size and you end up with poor image quality on many web sites. Microsoft's Internet Explorer has supported ColorSync on the Mac since version 4.x. At this time, Netscape still does not support ColorSync (as of version 4.5). This does not mean you cannot manage color going to the web, you just have much less control. To tag images (include profiles) that are going to the web, HTML commands are available. See the following links for more information:
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