Non-destructive (undo-able and infinitely redo-able)

• Use layers
• Select and use layer-masks (instead of cutting an image up)
• Duplicate a layer and keep a copy when applying filters.
• Or turn layer into smart objects. Then appy filters
• Paint into an empty layer
  
  
• Select and use adjustment layers (instead of directly changing the pixels)

• Image -> Adjustment -> 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.
  • 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.
  
  

- RGB: Red, Green, Blue
- When dealing with light

- CMY(K): Cyan, Magenta, Yellow, blacK
- When dealing with pigments

- Guess which color mode Photoshop uses?

- play around with color picker
- channels
- Image -> Mode ->

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

Reading the histogram -- many tools in photoshop asks you to deal with images through numbers.

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

  1. in the histogram tool, move the grey triangle (called midpoint gamma) to one edge to make it darker or lighter.

  2. click OK.

  3. re-open the histogram tool and see what happenend to the histogram. Do you see a comb pattern?
  
  

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.
    
    
  
  
  

[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.
  
  
• Solid Color

Layer masks

• Original Image (right side too dark)
  
  
  
  

  ---

  
  
  
• Brighten the image With adjustment layer
  
  
  
  

  ---

  
  
  
• Adjustment layer with layer mask
  
  
  
  

Right-click on the adjustment layer and select "Create Clipping Mask". Then the adjustment layer will only apply to the layer immediately below it.

1. With selection (Marching ants), create new adjustment layer






2. selection automatically converted to layer mask

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