"Digital Media Primer" Yue- Ling Wong, Copyright (c)2011 by Pearson EducaDon, Inc. All rights reserved.

Transcription

1 "Digital Media Primer" Yue- Ling Wong, Copyright (c)2011 by Pearson EducaDon, Inc. All rights reserved. 1

2 Chapter 3 Capturing and EdiDng Digital Images Part 3 Digital Image Retouching 2

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

4 Basic Steps of Digital Image Retouching 1. Crop and straighten the image 2. Repair small imperfecdons 3. Adjust the overall contrast or tonal range of the image 4. Remove color casts 5. Fine- tune specific parts of the image 6. Sharpen the image 4

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

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

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 7

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 reladve differences between colors. Brightness/Contrast tool will alter the reladve differences between colors. Thus, in general, adjusdng levels is preferred over the brightness/contrast tool. 8

9 Histogram A histogram is a bar chart that shows the reladve number of pixels ploaed against the color value 9

10 Histogram 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 10

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

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

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

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 14

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

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

17 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. 17

18 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. 18

19 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. 19

20 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. 20

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) 21

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

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

24 Example ApplicaDon 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. 24

25 Example ApplicaDon 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. 25

26 Example ApplicaDon 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. 26

27 Step 6. Sharpen the image Why? Scanned images usually look a liale sod- focused. Scaling an image also can make the image sod- 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... 27

28 Using Unsharp Mask 28

29 Don't Over- sharpen! 29

30 Try out: IMAGE RETOUCHING (LAB) Use the example image available from the book s Web site and pracdce the retouching steps discussed. 30

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 31

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 edidng program? What happens if you do the dodging and burning before removing the color casts? 32

33 Review QuesDons Note to instructor: Depending on your preference, you may want to go over the review quesdons at the end of this lecture as an instant review or at the beginning of next lecture to refresh students' memory of this lecture. 33

34 Review QuesDon 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 imperfecdons Fine- tune specific parts of the image using 34

35 Review QuesDon If the image has a green cast, how would you color correct it using Color Balance? 35

36 Review QuesDon Both of the following tools can be used to increase contrast. However, tool will alter the reladve differences between colors. A. Image > Adjustments > Levels... B. Brightness/Contrast 36