1. "Digital Media Primer" Yue-Ling Wong, Copyright (c)2013 by Pearson Education, Inc. All rights reserved.

2. Chapter 3 Capturing and Editing Digital Images
Part 3
Digital Image Retouching

3. In this lecture, you will learn
the basic steps of image retouching
the tools for image retouching steps

4. Basic Steps of Digital Image Retouching
Crop and straighten the image
Repair small imperfections
Adjust the overall contrast or tonal range of the image
Remove color casts
Fine-tune specific parts of the image
Sharpen the image

5. Step 1. Crop and Straighten
Why?
The image may be tilted.
You may only want part of the image.
Photoshop Tool:
Crop tool

6. Step 2. Repair Small Imperfections
Why?
Scanned images: dirt and dust
Photoshop Tools:
Clone Stamp
Healing Brush

7. Step 3. Adjust overall contrast or tonal range of the image
Why?
To maximize the tonal range of the image to improve contrast
Photoshop Tools:
Image > Adjustment > Levels...
Image > Adjustment > Curves...
Image > Auto Tone
Image > Auto Contrast

8. Adjust Levels vs. Brightness/Contrast
Adjust levels allows you to stretch the tonal range to improve image's brightness and contrast while maintaining the relative differences between colors.
Brightness/Contrast tool will alter the relative differences between colors.
Thus, in general, adjusting levels is preferred over the brightness/contrast tool.

9. Histogram
A histogram is a bar chart that shows the relative number of pixels plotted against the color value

10. Histogram of the image levels
An image with 4 colors
Histogram of the image levels
X-axis: the gray level (with the darkest value on the left)
Y-axis: the relative number of pixels in the image that have the corresponding shade of gray

11. Histogram of the image levels
Adjust Levels Example
An image with 4 colors
Histogram of the image levels

12. Stretching the histogram
Adjust Levels Example
An image with 4 colors
Stretching the histogram

13. Adjust Levels Example After adjusting levels
by stretching the histogram, the contrast of the image is increased.
Histogram after stretching

14. Brightness/Contrast Example
After adjusting levels
by stretching the histogram, the contrast of the image is increased.
Histogram after using Brightness/Contrast tool
Note the relative position of the color levels in the histogram

15. Step 4. Removing Color Casts
Why?
The image may contain color casts, i.e. appear tinted.
Photoshop Tools:
Image > Adjustments > Color Balance...
Image > Adjustments > Auto Color

16. Color Balance Example An image with a purple tint
Color Balance dialog box

17. The image after removing the purple tint
Color Balance Example
The image after removing the purple tint
Color Balance settings to remove the purple tint from the original image
To remove a color cast:
Move the sliders away from the label of the color that is the color cast you want to remove.

18. The image after removing the purple tint
Color Balance Example
The image after removing the purple tint
Color Balance settings to remove the purple tint from the original image
For example, the purple tint contains a red tint. Thus, the first slider is moved away from red to remove the red tint.

19. The image after removing the purple tint
Color Balance Example
The image after removing the purple tint
Color Balance settings to remove the purple tint from the original image
You may also choose to apply the color correction to the highlights, midtones, or shadows of the image.

20. The image after removing the blue tint in the darker areas
Color Balance Example
The image after removing the blue tint in the darker areas
Color Balance settings to remove the purple tint from the original image
For example, the shadow areas have more blue tint than the rest of the image. You can select Shadows and move the sliders away from Blue and Cyan to selectively remove the blue tint from the darker areas.

21. Step 5. Fine-tuning specific parts of the image
Why?
You may want to apply different effects on small parts of the image.
Photoshop Tools:
Dodge tool (to lighten by brushing)
Burn tool (to darken by brushing)
Sponge tool (to saturate/desaturate by brushing)

22. Step 5. Fine-tune specific parts of the image
Why?
There may be small distractions, such as power lines, small airplanes in the sky, a zit on the face.
Photoshop Tools:
Clone Stamp tool

23. Example Application of Dodge and Burn Tool
The image before fineturning with dodge and burn
The image after fineturning with dodge and burn

24. Example Application of Dodge and Burn Tool
The image before fineturning with dodge and burn
The image after fineturning with dodge and burn
The overexposed area is darken a little by burning.

25. Example Application of Dodge and Burn Tool
The image before fineturning with dodge and burn
The image after fineturning with dodge and burn
The shadows are burnt and the lighter areas are dodged to exaggerate the light and dark, thereby making the drum appear less flat.

26. Example Application of Clone Stamp Tool
The image before fineturning with the clone stamp tool
The image after fineturning the clone stamp tool
The paint on the drum is restored using the clone stamp tool.

27. Step 6. Sharpen the image Why?
Scanned images usually look a little soft-focused.
Scaling an image also can make the image soft-focused.
Even if your image is a straight digital photograph from a digital camera, it is a good idea to experiment with sharpening to see if it improves the image’s overall clarity.
Photoshop Tools:
Filter > Sharpen > Unsharpen Mask...

28. Using Unsharp Mask

29. Don't Over-sharpen!

30. Image Retouching (Lab)
Try out:
Image Retouching (Lab)
Use the example image available from the book’s Web site and practice the retouching steps discussed.

31. Order of the Steps Try to keep the order of the steps
Performing these steps out of order or jumping back and forth among steps may cause unwanted effects on the image

32. Order of the Steps
Why should the sharpening be one of the final steps in the process?
Why should cropping be the first step before you do anything to the image in the image editing program?
What happens if you do the dodging and burning before removing the color casts?

33. 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.

34. Review Question
Given here are the general steps of image retouching of a scanned image. Order the steps by labeling 1 through 6. ___ Remove color casts ___ Adjust the overall contrast or tonal range of the image ___ Crop and straighten the image ___ Sharpen the image ___ Repair small imperfections ___ Fine-tune specific parts of the image using 4 3 1 6 2 5

35. Review Question
If the image has a green cast, how would you color correct it using Color Balance?
move the second slide away from green, i.e., towards magenta

36. Review Question
Both of the following tools can be used to increase contrast. However, ___ tool will alter the relative differences between colors.
Image > Adjustments > Levels...
Brightness/Contrast
move the second slide away from green, i.e., towards magenta