Color Correction Primer

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My take on additive and subtractive color theories, a Photoshop color correction method, (3-click color) and a few odds and ends related to correctly printing from a digital photographic file.

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Color Correction Primer

  1. 1. Mr. Pixel’s Color Theory & Color Correction Tutorial © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  2. 2. Mr. Pixel’s Color Theory Primer & Color Correction Tutorial Color Models Color Modes Color Numbers Color Correction © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  3. 3. Color TheoryAdditive Color - TransmissiveSubtractive Color - Reflective © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  4. 4. Additive Color Theory RGBRed, green and blue wavelengths of light are added to blackand creates the colors our brains perceive. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  5. 5. Additive Color Theory RGBAn equal RGB mixture of additive light produces neutralgray values. An unequal RGB mixture produces color. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  6. 6. Additive Color Theory RGBMonitorsProjectionsSensorsFilm © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  7. 7. Subtractive Color Theory CMYKVarying percentages of cyan, magenta and yellow inks are applied towhite paper. This subtracts from the white paper.If the percentage is balanced, gray is the result. If the percentage isunbalanced, color is the result. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  8. 8. Subtractive Color Theory CMYKTheoretically equal amounts of cyan, magenta and yellow ink produceneutral gray.Inks contain impurities. These impurities produce browns instead ofgrays.Black ink is added to mitigate this issue. “K” identifies this ink. CMYK. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  9. 9. Subtractive Color Theory CMYKLithography is the prime example. Lithography is great technology butthere are two key issues to take into account as files are prepped forprinting: 1) Gamut. The range of reproducible colors. 2) Dot Gain. The amount of ink absorption. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  10. 10. Subtractive Color Theory CMYK 1) Gamut is adjusted by the 3-click color correction method. 2) Dot gain is controlled by sharpening.We correct files for the limitations of the chosen output technology. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  11. 11. Subtractive Color Theory GamutLithography and other forms of printing have limited reproductioncapabilities relative to the color range available in a digital image.16.7 million theoretical color choices are available in an 8-bit image andover 2 billion colors in a 16-bit image.Depending on the method used to define and measure ink gamuts, thereare between 500,000 and 1.5 million color choices using CMYK. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  12. 12. Subtractive Color Theory Dot GainThe ink dots spread and flatten upon impact causing a loss of sharpnessand color fidelity.There are many ways to sharpen a file. The Smart Sharpen Filter is agood beginning method for sharpening images. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  13. 13. Subtractive Color Theory CMYKNewsprintMagazinesPostersInk-Jet © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  14. 14. Color Relationships
  15. 15. Color Models Describes Color NumericallyRGB - Red - Green - Blue - LightCMYK - Cyan - Magenta - Yellow - Black - InksHSB - Hue/Color - Saturation/Richness - Brightness/Dark or LightLAB - Lightness - A (Red/Green) - B (Blue/Yellow) © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  16. 16. Color Modes Assign Valuesan intensity value - RGBan ink percentage - CMYKhow colors look to the human eye - L*A*B256 shades of gray - Grayscaleblack or white- Bitmap256 colors - Indexed3 channel grayscale for specialized printing - Multichannel © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  17. 17. PrintingReproducible ShadowsReproducible HighlightsRendering Intents © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  18. 18. PrintingThe best results are achieved by running ink density testsand creating custom paper profiles. But if you don’t want togo to the trouble... © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  19. 19. Printing...then the 3-click color method is an excellent alternative.This method sets the shadow and highlight endpoints tomatch the shadow and highlight gamuts of a printer andpaper combination.Also known as “setting the endpoints for output.” © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  20. 20. Printing Tutorial 3-Click Color Adding Noise Rendering Intent © Michael E. SternBuild A Better Photograph dot com 818-422-0696
  21. 21. PrintingThe following method works on any digital image. Some digital images work well withthe 3-click method while some images work better with a 2-click method. Experiencewill dictate which method is best for a particular image.
  22. 22. PrintingSelect Threshold from the bottom of the Layers Panelby clicking on the half black, half clear icon.This is the infinitely editable Threshold AdjustmentLayer.This is good.
  23. 23. PrintingMake sure you can see the Info Palette. Drag the Threshold’s slider all the wayleft and slowly drag back towards the center. When the black areas begin toappear, stop. With the Color Sampler Tool selected, click on this area.What are the values in the Info Panel?
  24. 24. PrintingDrag the slider all the way to the right and slowly drag back towards the center.When white areas begin to appear, stop. Click on this area. Note the numbers inthe Info palette. These pixel values are 254-255.After you click OK, turn off the Threshold Adjustment Layer in the Layers Panel.
  25. 25. Printing Setting target shadow and highlight values Shadows HighlightsOpen the Curves Adjustment Layer the same way you opened the Threshold Adjustment Layer.One at a time double-click each of the 3 eyedropper tools. The Target Shadow and Target HighlightColor dialog boxes open. In the RGB boxes and with the Shadow Eyedropper active, input 13 forthe shadows. Click OK. Do the same for the highlight numbers. Input 247. These numbers will varyfor different printer, paper and ink combinations. In this example the percentages are 5% and 97%.Middle gray is pre-set to 128. Do not change this number.Notice how the circle changes its’ position on the scale at the far left of the large red box.
  26. 26. PrintingWhen you have completed this step, click OK. Click Yes if you also get this dialog box.Look and you will see the Curves Adjustment Layer floating above your ThresholdAdjustment Layer and Background in the Layers Panel.
  27. 27. PrintingShift + Command (PC - Control) + N will bring up this dialogue box.Make note of the settings and click OK.Turn off the Curves Adjustment Layer. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  28. 28. PrintingSet the layer’s Blend Mode to Difference.
  29. 29. PrintingBoth adjustment layers off. Difference and Background layers on. Wax on. Wax off.Black is in reality middle gray because of how the Difference Blend Mode functions. Thegray pixels in the Difference layer cancel out the gray pixels in the Background layerthat are in registration with each other. Black is the result. Or close to it.This is a way to identify where the middle grays are in an image. With the EyedropperTool selected, (3x3 or 5x5) click on one or two target areas to set the point. Use the InfoPanel to monitor the targets. Try to get as close to equal as possible in all threechannels. This is important.
  30. 30. PrintingTurn off the Difference layer and turn Curves on.Threshold can be deleted.Re-open Curves by double-clicking its’ thumbnail icon.
  31. 31. Printing Highlight Mid-Tone ShadowSelect the shadow eyedropper and click on point one. Select the highlight eyedropperand click point two. Repeat for the middle eyedropper.That’s it. 3-click color at its’ finest. Experienced users can set the shadow and highlightendpoints by eye. If an image contains gray, skip the Difference Blend Mode layer stepsand click on the gray area with the middle eyedropper tool.
  32. 32. PrintingAn optional step with the Curves Adjustment Layer: select the mid point at the centerof the diagonal line. In the Input box type 128 if it’s not already set. Reducing theOutput number will darken the image. Increasing the Output number will lighten theimage. This is determined by taste and experience.I move in increments of ten. I’m usually ten up or ten down. Highlight the small blacksquare by clicking on it. Hold down the shift key (while pressing the up or down arrowkey) to move the point in increments of ten.
  33. 33. PrintingBefore After
  34. 34. Adding NoiseThe Histogram may look like this after 3-click color. This is called penciling orcombing. Click the refresh button to updatethe Histogram. This button will disappearafter refreshing.Gaps represent missing information. Whilethe file may appear OK on screen, bandingor posterization will most likely show up inprint. To prevent this, add noise (randompixels) to the file on a separate layer. Michael E. Stern PHOTOGRAPHY EDUCATION CONSULTING CyberStern.com
  35. 35. Adding Noise Make a new layer and input the settings shown here.Go to the Filter menu, select Noise and then select Add Noise. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  36. 36. Adding Noise2-3% for the amount. Makesure Distribution andMonochromatic are setaccordingly.Click OK.
  37. 37. Adding NoiseBefore © Michael E. SternBuild A Better Photograph dot com 818-422-0696
  38. 38. Adding NoiseAfter 3-click color correction, noise added and ahistogram refresh.
  39. 39. Rendering Intent Rendering intent aims to preserve numerical values, saturation levels or perceived color relationships. Perceptual is the preferred choice for photography in that by preserving color relationships one perceives a properly printed image. Colormetric aims to print colors per the assigned values in an image. When a color is out-of-gamut, the next nearest color is substituted. Usually a reject print. Saturation aims to preserve the richness of colors at the expense of accuracy and numbers. These are VERY simple explanations. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
  40. 40. © Michael E. SternBuild A Better Photograph dot com 818-422-0696

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