Digital Media Primer YueLing Wong Copyright c2013 by
"Digital Media Primer" Yue-Ling Wong, Copyright (c)2013 by Pearson Education, Inc. All rights reserved. 1
Chapter 3 Capturing and Editing Digital Images Part 4 Color and Tonal Adjustment 2
In this lecture, you will learn: • how to interpret image histograms • how to perform tonal adjustments on images • how to improve image contrast by stretching the histogram • how to use Curve Adjustment tool to adjust color and tonal range 3
Color Adjustment Tools • • adjusting the histogram color balance color curves hue/saturation 4
Histogram • A bar chart that shows the relative number of pixels plotted against the color value Histogram X-axis: the color value Y-axis: relative number of pixels that have the corresponding color value 5
Histogram Self-Test Exercise 6
Applying Histograms to Adjustment of Brightness and Contrast Move the sliders to modify the image’s brightness and contrast 7
Applying Histograms to Adjustment of Brightness and Contrast Define the darkest color (shadow) in the image Define the 50% intensity of the color (midtone) in the image Define the brightness color (highlight) in the image 8
Use of Shadow Slider • The originally second darkest color is now black. • Any color darker than this second darkest color is also black. the shadow slider has been moved to where the bar for the second darkest color of the image is 9
Use of Highlight Slider • The originally second brightest color is now white. • Any color brightest than this second brightest color is also white. the highlight slider has been moved to where the bar for the second brightest color of the 10 image is
Use of Shadow and Highlight Sliders to Stretch the Histogram • The originally brightest color is now white. • The originally darkest color is now black. • All other colors are mapped in between in the same relationship of their original gray tones. • Increased contrast 11
Photoshop's Image > Adjustments > Levels. . . 12
Use of Midtone Slider 13
Use of Midtone Slider • The third brightest color (originally a LIGHT gray) now is set to be the miidtone (i. e. the middle gray) • All other colors are remapped accordingly. • Overall tone of the image is DARKER. 14
Use of Midtone Slider 15
Use of Midtone Slider • The darkest color (originally a DARK gray) now is set to be the miidtone (i. e. the middle gray) • All other colors are remapped accordingly. • Overall tone of the image is LIGHTER. 16
Also see the interactive tutorial: UNDERSTANDING AND APPLYING HISTOGRAMS THERE ARE TWO PARTS OF THIS LEARNING AID: AN INTERACTIVE TUTORIAL AND PRACTICE EXERCISES. TUTORIAL: EXPLAINS HOW TO INTERPRET AN IMAGE’S HISTOGRAM AND MAKE TONAL ADJUSTMENTS USING HISTOGRAMS. PRACTIVE EXERCISES: EXERCISE I: READING HISTOGRAMS. EXERCISE II: IMPROVING IMAGE CONTRAST AND BRIGHTNESS. 17
Curve Adjustment Tool 18
Curve Adjustment Tool • Lets you remap the color and tonal range by using the shape of a 2 -D curve 19
Curve Adjustment Tool A diagonal line: No change in color/tonal range 20
Below the Diagonal Line Darken A curve below the diagonal line: The color/tonal values will be lowered 21
Above the Diagonal Line Brighten A curve above the diagonal line: The color/tonal values will be increased 22
Above or Below the Diagonal Line Brighten or Darken Part of the curve is below the diagonal line and the other part above the line 23
Above or Below the Diagonal Line Brighten or Darken Below the diagonal line: The color/tonal values within this range will be lowered 24
Above or Below the Diagonal Line Brighten or Darken Above the diagonal line: The color/tonal values within this range will be increased 25
Steeper Curve Increase Contrast A steeper curve: The in color/tonal range will be widened—higher in contrast 26
Less Steep Lower Contrast A less steep curve: The in color/tonal range will be narrowed—lower in contrast 27
Also see the interactive tutorial: UNDERSTANDING AND APPLYING CURVES FOR COLOR ADJUSTMENTS AN INTERACTIVE TUTORIAL AND EXERCISES HELP YOU UNDERSTAND THE CURVES TOOL FOR IMAGE ADJUSTMENT. 28
Review Questions Note to instructor: Depending on your preference, you may want to go over the review questions at the end of this lecture as an instant review or at the beginning of next lecture to refresh students' memory of this lecture. 29
Review Question Match each of the bars in the histogram to the color it represents. A B C ii i 30
Review Question To maximize the contrast and tonal range of this image, what changes of the sliders should be made? 31
Review Question Predict the resulting grays that are caused by the adjustment made to the image (shown in the histogram). Specify whether it is black, white, or gray. If it is gray, estimate an RGB value for that gray. A B C 32
Review Question Predict the resulting grays that are caused by the adjustment made to the image (shown in the histogram). Specify whether it is black, white, or gray. If it is gray, estimate an RGB value for that gray. A B C 33
Review Question After the adjustment, the image will be ___. A. brighter B. darker 34
Review Question ___ of the curve is steeper than the default diagonal line, and thus after the adjustment, the contrast for the tonal range within that region will be ___. A. B. C. D. Region A; higher Region A; lower Region B; higher Region B; lower 35
Review Question After the adjustment, the highlights (Region C) will become ___. A. brighter B. darker 36
Review Question After the adjustment, the shadows (Region A) will become ___. A. brighter B. darker 37
Review Question The curve in ___ is steeper than the default diagonal line, and thus after the adjustment, the contrast for the tonal range in that region will become ___. A. B. C. D. E. F. Region A; higher Region A; lower Region B; higher Region B; lower Region C; higher Region C; lower 38
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