Uploaded byMichael e. Stern Photography
Color Correction Primer
The document is a comprehensive tutorial on color theory and color correction, covering both additive (RGB) and subtractive (CMYK) color models. It details techniques for achieving optimal color reproduction in digital images for printing, including the 3-click color method for adjusting shadow and highlight values. Additional topics include noise addition to prevent banding, different rendering intents, and the significance of gamut and dot gain in the printing process.
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Color Correction Primer
- 1. Mr. Pixel’s ColorTheory & Color Correction Tutorial © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 2. Mr. Pixel’s ColorTheory 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. Color Theory Additive Color- Transmissive Subtractive Color - Reflective © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 4. Additive Color Theory RGB Red, green and blue wavelengths of light are added to black and creates the colors our brains perceive. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 5. Additive Color Theory RGB An equal RGB mixture of additive light produces neutral gray values. An unequal RGB mixture produces color. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 6. Additive Color Theory RGB Monitors Projections Sensors Film © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 7. Subtractive Color Theory CMYK Varying percentages of cyan, magenta and yellow inks are applied to white paper. This subtracts from the white paper. If the percentage is balanced, gray is the result. If the percentage is unbalanced, color is the result. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 8. Subtractive Color Theory CMYK Theoretically equal amounts of cyan, magenta and yellow ink produce neutral gray. Inks contain impurities. These impurities produce browns instead of grays. 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. Subtractive Color Theory CMYK Lithography is the prime example. Lithography is great technology but there are two key issues to take into account as files are prepped for printing: 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. 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. Subtractive Color Theory Gamut Lithography and other forms of printing have limited reproduction capabilities relative to the color range available in a digital image. 16.7 million theoretical color choices are available in an 8-bit image and over 2 billion colors in a 16-bit image. Depending on the method used to define and measure ink gamuts, there are between 500,000 and 1.5 million color choices using CMYK. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 12. Subtractive Color Theory Dot Gain The ink dots spread and flatten upon impact causing a loss of sharpness and color fidelity. There are many ways to sharpen a file. The Smart Sharpen Filter is a good beginning method for sharpening images. © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 13. Subtractive Color Theory CMYK Newsprint Magazines Posters Ink-Jet © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 14.
- 15. Color Models Describes Color Numerically RGB - Red - Green - Blue - Light CMYK - Cyan - Magenta - Yellow - Black - Inks HSB - Hue/Color - Saturation/Richness - Brightness/Dark or Light LAB - Lightness - A (Red/Green) - B (Blue/Yellow) © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 16. Color Modes Assign Values an intensity value - RGB an ink percentage - CMYK how colors look to the human eye - L*A*B 256 shades of gray - Grayscale black or white- Bitmap 256 colors - Indexed 3 channel grayscale for specialized printing - Multichannel © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 17. Printing Reproducible Shadows Reproducible Highlights RenderingIntents © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 18. Printing The best resultsare achieved by running ink density tests and creating custom paper profiles. But if you don’t want to go to the trouble... © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 19. Printing ...then the 3-clickcolor method is an excellent alternative. This method sets the shadow and highlight endpoints to match the shadow and highlight gamuts of a printer and paper combination. Also known as “setting the endpoints for output.” © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 20. Printing Tutorial 3-Click Color Adding Noise Rendering Intent © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 21. Printing The following methodworks on any digital image. Some digital images work well with the 3-click method while some images work better with a 2-click method. Experience will dictate which method is best for a particular image.
- 22. Printing Select Threshold fromthe bottom of the Layers Panel by clicking on the half black, half clear icon. This is the infinitely editable Threshold Adjustment Layer. This is good.
- 23. Printing Make sure youcan see the Info Palette. Drag the Threshold’s slider all the way left and slowly drag back towards the center. When the black areas begin to appear, stop. With the Color Sampler Tool selected, click on this area. What are the values in the Info Panel?
- 24. Printing Drag the sliderall 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 in the Info palette. These pixel values are 254-255. After you click OK, turn off the Threshold Adjustment Layer in the Layers Panel.
- 25. Printing Setting target shadow and highlight values Shadows Highlights Open 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 Highlight Color dialog boxes open. In the RGB boxes and with the Shadow Eyedropper active, input 13 for the shadows. Click OK. Do the same for the highlight numbers. Input 247. These numbers will vary for 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. Printing When you havecompleted 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 Threshold Adjustment Layer and Background in the Layers Panel.
- 27. Printing Shift + 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. Printing Set the layer’sBlend Mode to Difference.
- 29. Printing Both adjustment layersoff. Difference and Background layers on. Wax on. Wax off. Black is in reality middle gray because of how the Difference Blend Mode functions. The gray pixels in the Difference layer cancel out the gray pixels in the Background layer that 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 Eyedropper Tool selected, (3x3 or 5x5) click on one or two target areas to set the point. Use the Info Panel to monitor the targets. Try to get as close to equal as possible in all three channels. This is important.
- 30. Printing Turn off theDifference layer and turn Curves on. Threshold can be deleted. Re-open Curves by double-clicking its’ thumbnail icon.
- 31. Printing Highlight Mid-Tone Shadow Select the shadow eyedropper and click on point one. Select the highlight eyedropper and click point two. Repeat for the middle eyedropper. That’s it. 3-click color at its’ finest. Experienced users can set the shadow and highlight endpoints by eye. If an image contains gray, skip the Difference Blend Mode layer steps and click on the gray area with the middle eyedropper tool.
- 32. Printing An optional stepwith the Curves Adjustment Layer: select the mid point at the center of the diagonal line. In the Input box type 128 if it’s not already set. Reducing the Output number will darken the image. Increasing the Output number will lighten the image. This is determined by taste and experience. I move in increments of ten. I’m usually ten up or ten down. Highlight the small black square by clicking on it. Hold down the shift key (while pressing the up or down arrow key) to move the point in increments of ten.
- 33. Printing Before After
- 34. Adding Noise The Histogrammay look like this after 3- click color. This is called penciling or combing. Click the refresh button to update the Histogram. This button will disappear after refreshing. Gaps represent missing information. While the file may appear OK on screen, banding or posterization will most likely show up in print. To prevent this, add noise (random pixels) to the file on a separate layer. Michael E. Stern PHOTOGRAPHY EDUCATION CONSULTING CyberStern.com
- 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. Adding Noise 2-3% forthe amount. Make sure Distribution and Monochromatic are set accordingly. Click OK.
- 37. Adding Noise Before © Michael E. Stern Build A Better Photograph dot com 818-422-0696
- 38. Adding Noise After 3-clickcolor correction, noise added and a histogram refresh.
- 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. © Michael E.Stern Build A Better Photograph dot com 818-422-0696