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Extended Studies - Intro to Adobe Photoshop
11/4/15 Instructor: Kristy Depper E-mail: [email protected] 1
Working with Curves Curves are the Swiss Army knife of Photoshop. They’re great for adjusting both the contrast and color balance of an image in one window. They can lighten and darken areas without selections and they can pull out far more detail than is possible to see with the sharpening filters. None of these could be accomplished with Levels or Brightness/Contrast without making selections.
In the Curves adjustment, you adjust points throughout an image’s tonal range. Initially, the image’s tonality is represented as a straight diagonal line on a graph. When adjusting an RGB image, the upper-right area of the graph represents the highlights and the lower-left area represents the shadows. The horizontal axis of the graph represents the input levels (original image values) and the vertical axis represents the output levels (new adjusted values). As you add control points to the line and move them, the shape of the curve changes, reflecting your image adjustments. The steeper sections of the curve represent areas of higher contrast while flatter sections represent areas of lower contrast.You can save Curves adjustment settings as presets.
Extended Studies - Intro to Adobe Photoshop
11/4/15 Instructor: Kristy Depper E-mail: [email protected] 2
Default Curves dialog boxes for CMYK and RGB images
A. Default orientation of CMYK tonal output bar B. CMYK Input and Output values in percentages C. Default orientation of CMYK tonal input bar D. Default orientation of RGB tonal output bar E. RGB Input and Output values in intensity levels F. Default orientation of RGB tonal input bar
Reading the curve: The curves dialogue box is really just a simple bar chart (with a lot of bars really close together) that shows how much ink or light will be used in your image.
• The bottom gradient represents the shades of gray you are changing. • The side gradient indicates how bright or dark a shade will become if you move the line to a
certain height.
Extended Studies - Intro to Adobe Photoshop
11/4/15 Instructor: Kristy Depper E-mail: [email protected] 3
Basic Technique (Understanding how it works): Unlike levels were you slide one of three sliders around to change the look of your image, Curves requires that you target a shade of grey first. You do this by clicking on the diagonal line (referred to as a curve), adding a point and pulling that point up, down, left or right. Click anywhere on the curve to add a point. Draw an imaginary line from the point to where it meets the bottom gradient in order to determine the shade of grey you are now editing/targeting. If you nudge the point up, either by dragging it with your mouse or using the arrow keys, you will lighten that shade of grey. (Figure 3a & 3b) **I’ve added shades of grey to help you visualize both the tone you are targeting and the tone it will become. In the real curves dialogue, the grey shading does not exist, nor is my shading very accurate.
Dragging the same point down will cause that shade of grey to darken. It will also cause the other shades to darken, and the shadows to potentially max out at black. (Figure 3c)
Extended Studies - Intro to Adobe Photoshop
11/4/15 Instructor: Kristy Depper E-mail: [email protected] 4
Tonal Adjustments: Increasing Contrast Basic: Adding contrast basically means lightening the highlights and darkening the shadows. In other words, making the difference between the bright and dark parts more pronounced. On a curve, this means causing the curve to have a steeper pitch. The S curve: Add a point to the curve at the 3/4 shadow point and drag it down. Then add a point to the curve at the 3/4 highlight area and drag it up
Advanced: Targeting specific areas You can target a specific tone in your image by moving your mouse out of the curve window and onto the image. When the cursor changes to an eyedropper, hold down the command key and click on the tone you want to change. To prevent the other tones from changing too, find the next lightest tone to your target where you don’t want the contrast to change and command-click on it to add that tone to the curve. This essentially locks off the upper range of the tones. Now do the same for the shadows (it’s entirely possible that there isn’t a darker shadow tone and that the next one is black).
To prevent this curve from changing the color as well as the contrast, set your curve adjustment layer to luminosity.
Extended Studies - Intro to Adobe Photoshop
11/4/15 Instructor: Kristy Depper E-mail: [email protected] 5
The Eyedroppers The eyedropper tools can be used to make initial color corrections and tonal adjustments. Almost all images have an area of pure black and pure white in them and if you’re lucky (or planned ahead and shot a grey card) you may even have a 50% grey value. You can use these areas to get a decent color balance and even adjust the tones. All you have to do is select the black eyedropper and click on the area in your image you would like to be pure black. Photoshop will adjust it (and all the other tones) accordingly. Now repeat this process with the white eyedropper. Changing the default values: You can set the output values for the black, grey and white eyedroppers by double clicking on each eye dropper to open the color picker. Enter your own RGB values or choose a color from the picker. Remember from Levels that the starting points for the Sheridan setup is as follows:
Black Point: R=7, G=7, B=7
White Point: R=247, G=247, B=247
Adjusting color through the Channels: Color can be targeted and adjusted in the same way we altered contrast. The hardest part about this is remembering what the complimentary colors are to each of the primary colors. First, switch channels from the RGB composite channel to one of the color channels. Now add a point to the curve and pull! Notice that if you pull the Red Curve up, you increase the amount of red in your image and if you pull it down, you decrease it (or increase the amount of cyan). The same is true for each of the channels, up increases the primary color and down increases the complimentary color. You can again target specific color groups by Command-clicking on that color in the image to auto-add a point precisely on the curve.
