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What is color Color Models Color and Computers Color Spaces and Gamut
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What is color Color Models Color and Computers Color Spaces and Gamut

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  1. What is color Color Models Color and Computers Color Spaces and Gamut Color Management Color Profiles Color Managed Workflow Capture Printing Digital ColorColor is just numbers in the computer until they are interpreted. Interpreting these numbers to obtain a predictable color image is what color management is all about. Frank Richards April 2011

  2. Color Models • Red, Green, Blue (RGB) is the color model used by computer monitors, TVs, scanners and digital cameras to combine light. • Human eye responds to RGB • All the colors added together provide white. • The absence of light yields black. • Cyan, Magenta, Yellow, Black (CMYK) is the color model used by printers to combine ink. • All the colors printed together provide black. Well, sort of: • CMY inks mix together to make a muddy brown-black. Black (K) is added to produce true blacks and grays. • The absence of color yields white.

  3. RGB Color Model • The RGB color system can be represented as a cube. RGB, CMY, black and white are on the corners. • The origin is Black (K). The diagonal is a gray gradient ending in white at the far corner. • Different colors are represented by unique color values (numbers) within the cube. • A color wheel is often used to represent the fully saturated colors.

  4. Color space is a color model for which a specific set of values describe a specific color. Color spaces can be either device-independent (e.g. Adobe RGB) or device-dependent (e.g. Epson 1280 printer using Matte HW paper) Common device-independent RGB color spaces are: sRGB IEC61966-2.1 - created by HP and Microsoft for images to be displayed on “typical” monitor. Used by many comercial labs. Adobe RGB 1998 - developed by Adobe as an alternative to sRGB to provide a better match to printers. It is a good general-use color space for images that will be output on a verity of devices. It encompasses sRGB and roughly 50% of the visible colors of light. ProPhoto RGB – developed by Kodak. Very large gamut designed for photo output. Includes all colors that are likely to occur in the real world and some that are not visible. Device-dependent color spaces describe the behavior of a specific device. They include color spaces for: Cameras, scanners, monitors, printers/papers… Commercial labs, offset presses… Color Spaces

  5. Color Spaces and Gamut • Gamut is the range of colors found within a color space. • sRGB was developed to provide a color space that matches the typical monitor. Is default color space for the internet. Used by most drug stores and commercial labs. • Adobe RGB was developed to better match printer capabilities. Is good general use working color space for images that will be output on a variety of devices. It is generally regarded as the best color space for photo inkjet printers. • Most digital SLRs provide a choice of either color space for jpeg’s. Suggest Adobe RGB capture unless images will only be processed in commercial labs or used on the internet. • Inkjet printers have limited gamut and each color spaces is unique. A printer’s color space depends on the type of printer and its settings, ink and paper. • Adobe RGB contains most of the photo inkjet printer’s gamut. sRGB does not.

  6. Capture Digital Camera Scanner Commercial Lab Internet/email Processing Processing Software Color Mgmt System Working Color Space Monitor Disk Storage Output Printer Projector Monitor Drug Store Commercial Lab Offset Press Internet/email We Work With Many Color Spaces • All of these devices and processing steps have their own color space. Each impacts the color of the final output. Each of these color spaces is described by a profile. • It is important to understand and control the color at each step in the workflow to obtain predictable results. This is the essence of a color managed workflow.

  7. What’s Next - Color Management Profile is a mathematical description of the color behavior of a specific color space. The computer uses profiles to translate color values into specific colors. Color Managed Workflow - Manage color as it’s moved between image capture, display, processing and output Interpret color spaces Convert between different color spaces Color Summary Color model is general system of assigning values (numbers) to colors. e.g. for RGB, the three primary colors in visible light define a color. Color space is a color model for which a specific set of values describe a specific color. (The terms space and model are sometimes used interchangeably.) Gamut is the range of colors found within a color space.

  8. Color Profiles • Color profiles are used to translate color values into specific colors. Thus, color space gamut is defined by color profiles. The ICC provides the standards for color profiles which are usually referred to as ICC profiles. • ICC profiles can describe either a device-independent color space (sRGB or Adobe RGB) or a device-dependent color space. • Device-dependent ICC profiles are used to describe the color behavior (color space) of monitors, printers, etc. Profiles come in several varieties: • Canned – come embedded in the device (display or printer) and may be hidden • Generic – tailored to specific models, papers, etc. but not unique to an individual device • Custom – created for an individual device by user or service, e.g. display profile • Device-dependent ICC profiles may be provided by manufacturer, profiling services, or developed by the user, e.g. • Monitors – factory-calibrated, characterized with Adobe Gamma, or profiled with third-party software and colorimeter. • Printer –supplied with printer, provided by paper manufacturers, purchased custom profiles, or developed using third-party profiling software and spectrometer. • Image files are tagged with ICC profile to define the image color space. This embedded tag does not change the numbers, but rather tells the software how to interpret the color numbers. • International Color Consortium (ICC) was founded by Adobe, Agfa, Apple, Kodak and Sun to create standards for color management. ICC profiles are the standard across most devices and platforms today.

  9. Color Management System • Color management is all about defining how color values are interpreted from image capture through processing and output. • Color Management System (CMS) is the software that handles the interpretation and device-to-device conversion of colors. • A process is not color managed, if we do not control how the color is interpreted, e.g. putting a image out on a website.

  10. Image Processing Software Printer A Uses canned printer profiles Color Management System Raw Processing Camera Color Space(JPEG/TIFF) RAW Working Color Space Printer B Uses ICC profiles ProShow pass through Projector sRGB device Monitor Calibrated Profiled RGB Color Management JPEG/TIFF

  11. Photoshop - Color Settings • Color Settings can be found in Photoshop under Edit > Color Settings • It sets default color working space, color management policies and conversion options. • Adobe RGB is good default RGB working space for general use. CMYK, Gray and Spot working spaces are only for offset press work – accept defaults. • Color management policies define how Photoshop handles ICC profile mismatches. • Conversion options - suggest using: • Adobe ACE engine is industry standard. • Relative colorimetric or perceptual rendering intent. • Black point compensation and dither. • Advanced Controls • Suggest leaving both unchecked. • Name and save your color settings

  12. JPEG camera images are converted and tagged with a color profile. Images are processed in-camera for either sRGB or Adobe RGB color space. Recommend capturing image with a color space that will encompass all intended uses. Adobe RGB best for multi-purpose use. For RAW capture, color space and bit depth are assigned to image when processed. Photoshop CMS converts camera profile to working space, if different, for processing. Raw Processing Working Color Space Color Managed Workflow - Capture Color Management System Camera Color Space (JPEG/TIFF) RAW JPEG/TIFF

  13. Our objective is a predictable relationship between the image as viewed on monitor and the print. Inkjet printer interface is RGB and they are treated as RGB devices. All printers are inherently a CMYK devices. Printer driver and firmware make the RGB to CMYK conversion. Image processing software generally allows us to send color values to printer with either: A device-independent profile to be used with a canned printer profile (Printer A) A generic or custom printer profile (Printer B) Working Color Space Color Managed Workflow - Printing Printer A Uses canned printer profiles Color Management System Monitor Calibrated Profiled Printer B Uses ICC profiles

  14. Printer Determines Colors(Printer A) • Printer drivers, firmware and settings determine image colors when using in-printer processing. • In-printer processing works well with manufacture's ink and paper. • If settings for specific paper and ink combination are not available, try choosing a similar one and adjust printer controls for best results. This changes the internal canned profile. Save settings for later use. • In Photoshop, • Choose Let Printer Determine Colors from File>Print menu. • Set rendering intent. • In printer control panel, • Select paper type. • Adjust other settings as needed. • Adobe RGB working space is good match for inkjet printers. But, some printers may not recognize Adobe RGB when using in-printer processing. So experiment.

  15. Printing - Photoshop Determines Colors(Printer B) • Most of today's printers are calibrated and stable, so generic profiles work well. • Generic printer ICC profiles are unique to printer model, printer settings, ink and paper. Generic profiles can usually be obtained from: • Printer manufacturer. • Third party ink or paper maker. • In Photoshop, • Choose Let Photoshop Determine Colors from File>Print • Select ICC profile for printer and paper. • Choose rendering intent and black point compensation. • In printer control panel, • Turn off printer color processing. • Select paper type and printer settings as instructed in profile documentation. • Generic or custom profiles are not necessarily better than the letting printer determine color.

  16. Our objective is to achieve predictable results using a color managed workflow. Not possible to match output to capture or monitor due to viewing medium and hardware limitations. Focus on the final image, not the numbers. Bottom line thoughts for color managed workflow Entire workflow uses RGB color model. Capture (JPEG or RAW) – choose color space and bit depth Good – in-camera processing for 8 bit, Adobe RGB, JPEG image Better – RAW capture saved as 16 bit, Adobe RGB image Use color managed image processing software (Elements or Photoshop) Set Color Settings defaults and use Adobe RGB working space. Display Problematic to good – use as delivered Better - profile monitor regularly Printing Good to very good - Let printer determine the color using manufacturer’s ink and paper Better - Use generic or custom profile for selected printer, ink and paper combination with Photoshop managing color. Select rendering intent and set black point compensation Projected image – convert image to sRGB and embed profile Achieving Predictable Output

  17. Sizing an Image Original image (8.6 MP) Resized to print without changing pixels (8.6 MP) Reduced pixels for projected image (7.0 MP) Resized to print at higher resolution. Increases pixels (34.6 MP)

  18. Large Gamut Color Spaces Adobe RGB • Encompasses most of the colors that can be reproduced by common output devices today. • But, most cameras can capture colors that exceed the Adobe RGB gamut and inkjet printers continue to improve increasing output gamut. ProPhoto RGB • Can neither view or print the available colors. • As technology progresses, we might be able to capture and reproduce more colors in the future. Capable of preserving all likely occurring colors. • Because the space is so large, we have more elbow room, but fewer levels with which to work. • Need to be careful performing edits because of larger gaps each color level. Use 16 bit color depth to minimize banding.

  19. RGB Color Image • Each pixel has values for the three primary colors of light - RGB. The pixel color is the combination of these primaries. • In Photoshop, each of the primary colors is represented by a gray scale image where black masks the color. • Shades of gray provide the illusion of continuous tone. • For 24 bit color, the three channels combine to create 16.8M colors. The human eye can distinguish about 1.2 M colors.

  20. Color SpaceMakes A Difference Adobe RGB image processed as sRGB. This changes the way values are interpreted resulting in an altered image color. This is what happens if we send an Adobe RGB image to the drug store for a print. Master Image in Adobe RGB Colors can change when we convert to a different color space. This shows the image as it would appear on paper using an Epson R2400 printer and Matte HW paper.

  21. Adobe RGB interpreted as sRGB

  22. Adobe RGB Master

  23. Matte Print