North Texas PC User

1
North Texas PC Users Group

• Photoshop SIG
• Hillary Morgan Ferrer
• Session 3 - August 18, 2007

2
What we will cover today

• Color Theory
• Histograms
• Exposure
• Correcting for Exposure
• Correcting for Color

3
COLOR
4
Color Theory

• The Color Wheel
• Really Young Girls Can Become Mothers
• Boys make really young girls cry
• To take out x you add y

5
Color Opposites

• To take out Red, add Cyan
• To take out Green, add Magenta
• To take out Blue, add Yellow
• And Vice Versa
• (examples in PS)

6
Ways to Manipulate Color in Photoshop

• Levels
• Curves
• Hue/saturation
• Selective Color
• Color Balance
• Photo Filters
• Channel Mixer

7
How Photoshop sees Color

• Photoshop sees color in terms of numbers
• These numbers are graphed onto a graph called a
  histogram
• 8 bits 256 shades
• 0 - 255
• 0 black
• 255 white

8
Histograms

• For each color, you have this histogram telling
  you how much of which shade of each color the
  picture contains.
• The colors exist in something called Channels
• RBG, CMYK

9
Normal Histogram

• No excess of bright whites
• No excess of Dark Darks

10
Bright White Histogram

• Picture is predominantly white, so we see a
  predominant number of pixels on the right side of
  the histogram

11
Dark Histogram

• Picture predominantly black, so we see a
  predominant number of pixels on the dark end

12
Correcting Exposure

• Levels
• Slide on RGB scale
• Slide on R,G,B scale
• Black point, white point droppers
• Finding Black/White points with alt
• Shifting midtones

13
Correcting Exposure

• Curves
• Overall darken/lighten
• Contrast curve

14
Over/Under
15
Over/Under Corrected
16
White Balance

• Makes Colors Neutral
• Bright Sun, Cloudy, Open Shade, Tungsten, Flash,
  Strobe, Halogen
• MUST do before with JPG
• Can do post with RAW
• Measured in degrees Kelvin
• Higher the degrees, the bluer it looks
• Lower the degrees, the redder it looks

17
Light Temperatures

• Open Shade/Cloudy - 6500
• Direct Sunlight - 5600
• Fluorescent - 3400-3800
• Tungsten - 3200

18
Shot on Cloudy Day
19
Eyedroppers in Levels
20
Ways to neutralize color in PS

• Even when color balance in camera, can still get
  color cast
• Gray card
• Eye dropper in curves, levels
• Auto color
• By sight (assuming you have calibrated monitor)
• Example (John roar)

21
Homework