Photoshp: Image -> Adjustments -> Levels

• Generally, a good quality image has wide range of colors (from darks to lights)
• Don't trust your eyeballs too much. It's only a reference.
  • Importance of using numeric tools
    
  • What we see is not necessarily what we have (notice the difference in color of all the TV monitors when you go to an electronic store).
  • Output devices (eg. monitors) cannot display all colors recorded.

Wrong (destructive) way:

• Image -> Adjustments -> Levels (or Apple L)
  
  

The color of each pixel is described using certain number of 0s and 1s.
Number of bits used to describe a pixel is called bit depth.

1 bit image: uses 1 bit (0 or a 1) to represent a pixel. Usually black or white.

• 0: black
• 1: white

In photoshop, (for historical reasons) this is called bitmap mode.
- Image -> Mode -> Bitmap
- Check out the Channels panel

Uses 8 bit to represent the color of a pixel.
8 bit image: 2^8 = 256 possible values for each pixel.

• 00000000 to 11111111 in binary
  
• 0 to 255 in decimal
  
• usually 256 shades of gray
  • 0: black
  • 64: dark gray
  • 128: mid gray
  • 192: light gray
  • 255: white

In Photoshop this mode is called Grayscale
- Image -> Mode -> Grayscale
- Check out the Channels panel

24 bit image (Photoshop calls it 8 bits/channel)

• 8 bits for red channel.
• 8 bits for green channel.
• 8 bits for blue channel.
• 16 million possible colors.

- Image -> Mode -> {RGB Color, 8bits/channel}
- Check out the Channels panel

• r, g, b: (in 8 bit/channel)
• 255, 0, 0: red
• 128, 0, 0
• 64, 0, 0
• 0, 255, 0: green
• 0, 128, 0
• 0, 64, 0
• 0, 0, 255: blue
• 0, 0, 128
• 0, 0, 64
• 255, 0, 255: magenta
• 0, 255, 255: cyan
• 255, 255, 0: yellow
• 128, 128, 128:
• 64, 64, 64
• 0, 0, 0

Photoshop: image-> mode -> {8 bits/channel, 16 bits/channel}

8 Bits / Channel => 16777216 colors
16 Bits/ Channel => 281474976710656 colors
32 Bits/ Channel => 79228162514264337593543950336 colors

Note that you can discard color information:

RGB 16 bits/channel -> RGB 8 bits/channel -> Grayscale -> Bitmap

But if you go the other way you won't get the colors back

Your scanner only gives you a starting point. It is an imperfect image. You will need to fix these imperfections.

• 1. Capture from scanner, download from camera
• 2. Global tonal/color correction
• 3. Remove noise, dust
• 4. Burn & dodge, local adjustments
• 5. Save.... and this becomes your master/source image.
• By this point, I'd convert to a 8 bits / channel image
  
  
• Fix the biggest problem first

Destructive tools -- Photoshop's traditional tools for global tonal/color correction (under Image -> Adjustments)

• Avoid it if you can. You will lose data (eg. rounding off floating points).
• More operations you do in Photoshop, more data degradation.
• Minimize operation or defer commitment.

Non-destructive Editing -- Use Adjustment Layers

• Layer -> New Adjustment Layer
• or in the Layer's panel. click the black and white circle.
  
  
  
  
  Adjustment Layers
  

  • Deferrs action.
  • It's like filters you put on lights to change color of light.
    • You are not changing the light bulb itself.
  • Not permanent until you "flatten" an image
  • You can change your mind as many times as you like, and not degrade quality
  
  
  
  • Eyeball -- activate/deactivate layer
  • Current layer -- highlighted blue. This is the selected layer.
  • Double-click on adjustment layer to re-adjust again and again w/o loss.
  • Change Opacity to vary strengh
    
    
    Levels adjustment layer
    
    
    
    
  • You can stack (adjustment) layers on top of each other.
    
    
  
  
  

Once you are done and ready to commit:

• save the layered version file (un-flattened) as a PSD
• save the flattened (commited) version as a TIFF
  • pulldown menu on the top right corner of the layers panel -> Flatten Image
  • or, Layer -> Flatten Image
  
  
  

[Adobe TV: improving tonal quality with levels]

Black(1), midpoint gamma(2), white point(3) slider

• Option-drag to see clipping area
• Clipping is destructive

Setting neutral white(6), neutral gray (5), and black(4) target points

• If you know some area that should be neutral {white, gray, black}, color correct using target points.

• Can do everything Levels, Brightness/Contrast, Color balance can, and more. (In the old days, it was said that if you master curves you won't need most of the tools in adjustment menu.
  • checkout Presets
  • "S" curve: increases contrast
  • reverse "S" curve: reduces contrast
  • Click on image to see where it corresponds on curve.
  • Option-Click to create point.

• Hue/Staturation
  • Selective/local correction by going to individual channels
  • Select a range of colors you want to modify
• Vibrance
  • Vibrance maintains the colors that are already brightly saturated and increases saturation in other areas.
• Brightness/Contrast
  • Intuitive.

Layer masks

• Original Image (right side too dark)
  
  
  
  

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• Brighten the image With adjustment layer
  
  
  
  

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• Adjustment layer with layer mask