Best Practices In Color Reproduction

Transcript

Best Practices in Color Reproduction Best Practices in Color Reproduction Presented by Joe Marin Senior Prepress Technologist/Instruction Using the Software • Chat box – please send questions to “host & presenter” • Raise hand in participant box to ask verbal question during Q&A periods • Switch to full screen if desired –icon in lower right hand corner, looks like one rectangle within another –access chat box and participant box from floating icons –return to partial screen with reverse arrow icon Color Management • Many printers will (or already have) implement color management into their workflow • Color management works, but only if the entire process is consistent and repeatable –A profile represents a color fingerprint of a device at a moment in time 1 Best Practices in Color Reproduction Survey Says… • From the PIA/GATF Research and Technology Report titled “The Pain of Color Management”: The number one problem in implementing color management into the workflow was… Process control Another Survey Says… • From another PIA/GATF/NAPL survey, the number one reason for reprinting jobs was… Excessive color variation Admit there is a problem 2 Best Practices in Color Reproduction Admit there is a problem • The first step in implementing process controls is to analyze your workflow and identify problems –What is your plate remake rate? –On average, how many proofs do you remake per job, and why? –Do your proofs match the printed sheet? –Is your pressroom running color consistently? Process Controls: What it is • Controlling the variables through measurement and documentation to achieve consistency, repeatability, and best possible product quality Process Controls: What it isn’t • An easy thing to implement –Uh-oh…this means change! • There will be resistance –Management must be committed to the process • There must be procedures –Staff must be committed to the process • There must be documentation 3 Best Practices in Color Reproduction Get it under control! Consider all processes... • We must control all steps of the color reproduction process –Color viewing –Scanning –Digital proofing –CTP –Press Understand color and educate your clients Process Controls for Color • Color –A phenomenon of light –A visual sensation • So what’s the problem? 4 Best Practices in Color Reproduction Color –The visible spectrum ranges from approximately 400 nanometers (blue) to 700 nanometers (red) • A nanometer is one billionth of a meter • The human eye can’t perceive energy outside this range –People who can’t distinguish between primary colors within this range are referred to as color deficient • 8 to 10% of the male population is color deficient • Only 1/2 of 1% of the female population is color deficient Color Perception • All people involved in the color reproduction process should take a color deficiency test –1. Production people –2. Customer service representatives –3. Sales personnel –4. Client (The client is the color expert!) • The leading color deficiency test is the Pseudo-isochromatic Test for Color Perception –www.richmondproducts.com Color Perception Images from the Pseudo-isochromatic Test for Color Perception www.richmondproducts.com 5 Best Practices in Color Reproduction Subtractive Color Reproduction • Subtractive color is the process of removing colors from the white surround • The subtractive color system works best with a white background –The whiter your paper is, the more colors you can reproduce (wider color gamut) Color is dependent on... • 1. Light –5000 Kelvin • 2. Object –Absorption and reflection characteristics • 3. Sensor –Eye Describing Color • Describing the visual sensation of color is as difficult as our other senses –Taste –Touch –Smell –Hearing 6 Best Practices in Color Reproduction Color Communication • Customers often find it difficult to describe the colors that they want… –Finding it easier to describe what the don’t want! “I can’t tell you what I want until I see it.” Communicating Color • Communicating the phenomenon we call color is difficult • We sometimes use vague, crazy terms to describe color… –Flat –Muddy –Needs more snap –Too warm, too cold –Needs to jump off the page …which results in more proofing cycles! When there are color problems... 7 Best Practices in Color Reproduction When there are color problems... Scanner Press Inks Proof Paper Press operator Scanner operator Establish consistent color viewing conditions Color Viewing Specifications • In North America, we use the American National Standards Institute (ANSI) viewing conditions: –5000 Kelvin lights –A viewing booth (surround) painted with Munsell N8 gray paint Courtesy of GTI (Graphic Technology Incorporated) 8 Best Practices in Color Reproduction The Effect of the Surround • Viewing booths should be free of distractions that could influence color perception 9 Best Practices in Color Reproduction The Effect of Changes in Lighting • The same proof will look very different under different lighting conditions Fluorescent illumination Tungsten illumination 5000K illumination Judging Your Viewing Conditions • A popular (and inexpensive) tool for evaluating lighting conditions is the GATF/RHEM light indicator –Attach to every proof to indicate whether lighting conforms to 5000° K –Solid color indicates proper light source –Banding indicates color temperature is not 5000° K Don’t give your clients unrealistic expectations 10 Best Practices in Color Reproduction What is a Reproduction? Reproduction: A likeness or a close facsimile The Color Reproduction Process Observer Photography Color Separation Press 11 Best Practices in Color Reproduction Color Gamut Comparison –There are millions of different colors in the visible spectrum! Color Gamut Comparison –Unfortunately, some of these colors are lost when a scene is photographed— even the best slide film can only record 12,000 to 14,000 colors Color Gamut Comparison –Converting RGB data into CMYK means another reduction in gamut; a color proof can only show 7,000 colors 12 Best Practices in Color Reproduction Color Gamut Comparison –Reproduction with printing presses and CMYK inks results in a still smaller gamut of about 6,000 colors Know the secret to controlling color What is an acceptable variation? 13 Best Practices in Color Reproduction Controlling Color • Why are some colors harder to control than others? –Saturated colors are easy to control and keep consistent –Grays, browns, purples, and blues (and others!) give us a lot of difficulty! Dot Gain Why? Look at the Curve 0% 25% 50% 75% 100% Dot Area Original +5 Cyan +5 Magenta +5 Yellow 14 Best Practices in Color Reproduction The Curve 90M 80Y Dot Gain 80C 90Y 90C 80M 0% 25% 50% 75% 100% Dot Area Original +5 Cyan +5 Magenta Original +5 Cyan +5 Magenta 15 Best Practices in Color Reproduction Original +5 Magenta +5 Yellow The Curve Dot Gain 24C 57M 56Y 55C 71M 0% 25% 50% 75% 100% Dot Area Why Gray? • Midtone neutral gray is the most volatile color to print • What is a midtone gray? –50% Cyan –40% Magenta –40% Yellow • If you print midtone neutral gray accurately, you can control the color 16 Best Practices in Color Reproduction Why Midtone Neutral Gray? • The midtone (50%) dot fluctuates the most on press • This is because the 50% dot has the greatest perimeter 20% dot 50% dot 80% dot Midtone Gray is the Apex Dot Gain 50C 40M 40Y 0% 25% 50% 75% 100% Dot Area The Secret to Accurate and Consistent Color Reproduction • Scan to gray • Proof to gray • Print to gray • If we can control neutral gray throughout the process, we can control the color! 17 Best Practices in Color Reproduction Optimize and calibrate your scanner Benchmarking Your Scanner • Benchmarking your scanner requires two sequential steps –Prequalification, then calibration • This process can save time and consumables costs –That come from re-scanning, making additional color proofs, etc. 1. Scanner Prequalification • Verify that the scanner can record a consistent signal level across the scan bed –Scan in a 25% gray card or a gray piece of paper –Measure the values of the scan in Photoshop for consistency • +-2% is acceptable 18 Best Practices in Color Reproduction 2. Scanner Calibration • Your color scanner can be calibrated by using a simple $5 device… • Need a transparent and reflective scale • Scanner calibration achieves proper tone reproduction and gray balance… The Grayscale: Live it! Love it! Use it! Tone Reproduction • Tone reproduction is contrast (the differences in brightness) –Is the only requirement for black-and-white Tone Reproduction +Highlight –Highlight Original +Shadow –Midtone 19 Best Practices in Color Reproduction Gray Balance • Gray balance refers to using CMY inks to produce a neutral gray –If it is incorrect, the color balance of the reproduction is said to have a “color cast” –Not needed for black-and-white work 50% K 50% C 40%M 40%Y Source: SWOP Gray Balance + Cyan + Magenta Original + Cyan and Magenta + Yellow Tone Reproduction & Color Balance C M Y K • Setting up your scanner to accurately reproduce the grayscale will give you: HL .05 5 3 3 0 MT .95 50 40 40 12 –Optimum tone reproduction –Optimum gray balance SH 2.00 90 80 80 70 20 Best Practices in Color Reproduction Output the Grayscale • Once you’ve scanned in and corrected the grayscale, output it on your proofing device • The goal is to match the grayscale on the proof to the grayscale original Original Proof –Once set, you are scanning to gray! Implement process controls in proofing Tools for Proofing • Maintaining consistency and repeatability during the color proofing process can be achieved by using a few simple tools –A PIA/GATF proof comparator –A spectrodensitometer 21 Best Practices in Color Reproduction The PIA/GATF Proof Comparator • This target is used to monitor and maintain consistency of digital proofing systems –Image on every proof and measure for consistency and accuracy Actual size: 1.8 X 6.3 in. Photo Montage • The photo montage is designed for visual assessment and comparison –The montage contains visually sensitive colors such as fleshtones, neutrals, and saturated colors • Visual comparisons should be made side-by-side under controlled lighting conditions Highlight/Shadow Reference Patches • Highlight patches (1%, 2%, 3%, 4%, 5%) • Shadow Patches (95%, 96%, 97%, 98%, 99%) –Use these target to determine if these “dots” were transferred successfully to the proof 22 Best Practices in Color Reproduction Black and 3 Color Gray Patches • Black and three-color tone patches –Three color grays can be compared to black only to insure neutral printing –This is measurable and visual 25C, 16M, 16Y 25K 50C, 39M, 39Y 75C, 63M, 63Y 50K 75K Measuring Black and 3 Color Gray Patches 25C, 16M, 16Y 25K 50K measurement 50C, 39M, 39Y 75C, 63M, 63Y 50K 75K 50K, 39M, 39Y measurement Tone Scales and Overprints • 25, 50, 75, and 100% tone values in CMYK and RGB –Use these patches to measure dot gain/dot area and solid ink density 23 Best Practices in Color Reproduction Implement process controls in platemaking Perform a Uniformity Test • A uniformity test shows imaging consistency across the entire plate • Image a 50% screen tint –Measure the plate at the center and corners –Measurements should be ± 1% 50% tint Perform an Accuracy Test • The accuracy test shows how well the platesetter is capable of rendering all tones accurately –Image a linear plate –Measure the tone scale on the test form –Measurements should be ± 1% 24 Best Practices in Color Reproduction Maintaining Consistency • Once the three quality control tests are completed, consistency must be maintained –GATF plate control targets • Analog and digital –Plate densitometer • These targets must be on every plate –Put the digital target on your imposition templates GATF Digital Plate Control Target • A native PostScript image used to monitor electronic imaging devices such as imagesetters and platesetters • Using the elements in the GATF plate control target, you can measure... Informational Block • • • • • • Imaging device used to output the target Horizontal and vertical resolutions Screen ruling Screen angle Dot shape PostScript version 25 Best Practices in Color Reproduction Checkerboard Pattern • 1, 2, 3, and 4 pixel checkerboard patterns –Each made up of equal parts image and background • When imaged correctly, each block forms a square with equal height and width Highlight/Shadow Reference Patches • An upper set which bypasses any calibration curve applied at the RIP • Lower set contains the correct values applied by your curve at the RIP Tone Scales • An upper set which bypasses any calibration curve applied at the RIP • Lower set contains the correct values applied by your curve at the RIP 26 Best Practices in Color Reproduction Plate Tolerances • Plate measurements should be within ±1% Plate Tolerances Variance • Plate measurements should be within ±1% +2% -2% Pressrun Plate Tolerances • Plate measurements should be within ±1% Variance +4% +2% -2% -4% Pressrun 27 Best Practices in Color Reproduction Processor Maintenance • Processor maintenance is key to consistent plate output from prepress –Most systems require some daily maintenance • Drain water, wipe transport rollers –Perform full maintenance according to your manufacturers recommendations • Usually based on square footage Implement process controls in the pressroom Process Controls in the Pressroom • Controlling and characterizing print conditions on press requires the following tools –A color bar –Spectrodensitometer 28 Best Practices in Color Reproduction Use a Color Bar! • The color bar must contain the following patches for measurement –Solid ink density • 100C, 100M, 100Y, 100K –Dot gain • 50C, 50M, 50Y, 50K –3 Color gray patch to measure gray balance • 50C 40M 40Y Solid Ink Density • Is the numerical measure of how much complementary light is absorbed by a color bar as measured with a spectrophotometer or spectrodensitometer Measuring Dot Gain • Dot gain should be measured at 50% because this is the dot that grows and fluctuates most on press –The 50% dot has the greatest perimeter 20% dot 50% dot 80% dot 29 Best Practices in Color Reproduction Dot Gain is Mechanical and Optical • Mechanical –The physical enlargement of halftone dots during the image transfer process caused by absorption of the ink by the paper • Optical –Light scatter around and under the dots results in an optical increase in dot size Gray Balance • Reproducing neutral gray with the three process color inks is referred to as gray balance 50% K 50% C 40%M 40%Y Source: SWOP Why the 50% and Midtone Gray? Dot Gain 50C 40M 40Y 0% 25% 50% 75% 100% Dot Area 30 Best Practices in Color Reproduction Print Contrast • Print contrast is the density difference between the solid of a process color and 75% tint area –The greater the difference, the better shadow rendition and detail Make it all work together 31 Best Practices in Color Reproduction Bring it all together! • Okay, so you’ve implemented process controls in proofing, CTP, and the pressroom • Next, you’ll learn how to get your digital proof to match the press sheet Bring it all together! • Getting the proof to match the printed sheet requires you to look at multiple production stages together Get the Press to Print to a Guideline • This involves building curves at the platesetter to compensate for less than ideal press conditions • The guidelines on the next slide represent printing conditions for various types of printing –As defined by industry groups SWOP and GRACoL 32 Best Practices in Color Reproduction The Step-by-Step Process 1. Image linear plates (PIA/GATF Test Form) 2. Run the linear plates on press and analyze the press sheets (measure the tone scales) 3. Curve the plates to get the press to print to a guideline (SWOP, GRACoL, etc.) 4. Image curved plates (for each color) 5. Run the curved plates on press and analyze the press sheets (match to guideline) 6. Use the measured results of step #5 to calibrate your digital proof 1. Image & Run Linear Plates • The only way to determine exactly how the press prints is to image linear plates and run them on press –Linear means that the a 50% tint on the plate measures 50%, 25%=25%, 75%=75%, etc. • Image a PIA/GATF Test Form 33 Best Practices in Color Reproduction 2. Analyze the Linear Press Sheets • Measure the press sheets –Read the tone scales on the test form • Determine where the press is printing and compare that to the specification you’re shooting for –Total dot gain 3. Measure the Press Sheet at the 50% • For example… –You measure the black 50% patch, and it reads 67% –SWOP requires the black to print at 72% K C M Y –This means that a 5% bump must be built into the plate at the 50% 34 Best Practices in Color Reproduction These Values Are Critical! • Printing to these dot gains means that you are printing to gray –Tolerance for dot gain is ±3% all colors, equally K C M Y K C M Y –Tolerance for solid ink density is ± .10 4. Curve the Plates • Once the difference between the specification and the press run is determined, curve the plate(s) –Build curves for each process color if necessary 5. Run the Curved Plates • Run the curved plates on press • Run to your chosen printing guideline and measure the press sheet to verify the results • You should be printing to the guideline that you chose at this point 35 Best Practices in Color Reproduction Dot Gain Using the SWOP Guideline Measuring 50% K K Dot Gain Using the SWOP Guideline Measuring 50% C C 36 Best Practices in Color Reproduction Dot Gain Using the SWOP Guideline Measuring 50% M M Dot Gain Using the SWOP Guideline Measuring 50% Y Y These Values are Critical! 72% K 70% C 70% M 68% Y When you print to these values, the press sheet is perfectly neutral! Your tolerance is 3% up or down, all colors, equally! 37 Best Practices in Color Reproduction 6. Calibrate the Digital Proof • Now that you’re printing to a guideline, calibrate your digital proof • Analyze press sheets printed from the curved plates and use that data to calibrate the digital proof Advantages of this Process • Specifications are guidelines for the printing industry which represent practical, achievable printing conditions • Ability to match CMYK-build spot colors • Specifications are accepted throughout the printing industry • It gives your pressroom targets to print at –And not just “eyeballing” it! Use GCR 38 Best Practices in Color Reproduction Separate Color Using GCR • Help your pressroom run color more consistently throughout a pressrun by separating color images with GCR –Gray component replacement • This will require prepress and the pressroom to (gulp!) work together… Color Reproduction Considerations • When images are converted from RGB into CMYK, the halftone dots for the black ink are typically generated in one of three ways: –Conventional separation (no UCR or GCR) –Undercolor Removal (UCR) –Gray Component Replacement (GCR) • This choice determines how dark the black image will be, as well as how much cyan, magenta, and yellow ink will be printed Conventional Separation • This process causes only the darkest parts of the image to reproduce on the black plate • Other terms used to describe this result include high-key black and skeletal black 4 COLOR = CMY + BLACK 39 Best Practices in Color Reproduction Undercolor Removal • UCR reduces the amount of cyan, magenta, and yellow and increases the amount of black in areas where black is already present –UCR primarily affects the shadow areas of the image –UCR should not effect color areas 4 COLOR = CMY + BLACK Example shown is 300% UCR Gray Component Replacement • GCR also reduces the amount of cyan, magenta, and yellow and increases black • GCR is more aggressive; it replaces the gray component of the trichromatic colors with black 4 COLOR = CMY + BLACK Example shown is 80% GCR Trichromatic Colors • Trichromatic colors are those made up of different percentages of all three primary printing colors (CMY) Trichromatic red • The gray component of trichromatic colors is the level up to which all three primaries are equally present –The tertiary color is reduced and replaced with black Tertiary color 40 Best Practices in Color Reproduction Trichromatic Red with 100% GCR 3 color red (no GCR) 100% GCR Trichromatic Red with 50% GCR 3 color red (no GCR) 50% GCR UCA and GCR • UCA is the opposite of UCR –UCA is used in conjunction with GCR • UCA increases the amount of cyan, magenta, and yellow in the achromatic areas of an image –Which can increase the total ink coverage required for specifications such as SWOP, SNAP, etc. 41 Best Practices in Color Reproduction Original 80% GCR 300% UCR Original 300% UCR +5% M in midtones 80% GCR +5% M in midtones GCR Settings • Black Ink Limit and Total Ink Limit • UCA Amount controls how much CMY are put back into the shadow areas of an image 42 Best Practices in Color Reproduction Measure and document to control the process Measure, Document, and Control • The final step in the process is to analyze and track the entire workflow • Document any problems that arise –Points out areas where additional training may be required 43 Best Practices in Color Reproduction Process controls by the numbers • Keep log books in each area with a daily, weekly, and/or monthly checklist • Use these books to monitor things such as… –Digital proof calibration –Platesetter calibration –Solid ink values, dot gain –Chemistry changes –ph levels of fountain solution • Get started right away! Thanks for Listening! Brand new! Just published! Process Controls Primer 96 pages, full color $20 PIA/GATF member $30 Non member To order, visit www.gain.net Click on Bookstore and Products Or stop by the PIA/GATF Booth! Sources of Information • BRIDGS Color Handbook for the Graphic Arts • Specification for Web Offset Publications (SWOP) • General Requirements for Applications in Commercial Offset Lithography (GRACoL) • “Applied Densitometry”, Gretag Imaging • Process Controls Department, Graphic Arts Technical Foundation 44