Photoshop Lab colorspace

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Photoshop Lab colorspace

• A quick and easy 26 step process for enhancing
  your photos

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What is Lab color space

• All digital photos exist in a digital colorspace
• Photos by default exist in one of several RGB
  color spaces ( Adobe, sRGB, CMYK, Lab )
• Most users work in Adobe or sRGB by default
• These work well for most instances
• Why muck with Lab color space
• Lab has the power to make some powerful edits (
  color noise reduction, and sharpening )

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How can Lab do this

• Lab has 3 components
• L Lightness
• A A channel controls Red and Green color
• B B channel controls the Blue and Yellow
• By separating the color from the luminescence
  information some powerful manipulations difficult
  in other color spaces become possible if not easy

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Slicing and Dicing in Lab

• Easy powerful adjustments

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Open An Image

• Open image into photoshop
• For JPEG or Raw usual method
• For Photos with layers the image will be opened
  in the usual way but will need to be flattened
  prior to processing
• Good advice Once opened save under new name to
  protect original

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Convert to Lab colorspace

• Once again Image has to be single layer and
  option to flatten image may be present
• To convert click on the Image menu item at the
  top of the screen, point to Mode, a flyout menu
  appears Click on Lab color
• Left click on Background blue area and choose
  duplicate This creates Background copy layer

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Background Copy - Channels

• With the Background copy layer active (Blue)
  click on the Channels Tab.
• Lab Channels Lab Composite of all channels L
  - Lightness Channel (BW) a - a channel Red
  Green color info b - b channel Blue Yellow
  color info

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Seclection of a channel to view

• Click on the Lightness channel (blue area)
• Only that channel is highlighted (blue)
• The image is now BW showing the Lightness
  info.
• Note The image of the a and b channels is not
  very interesting that is apparently normal

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To Adjust Contrast Brightness

• Click on Layers menu item (top of screen)
• Place cursor on New Adjustment Layer
• In flyout menu click on Curves
• A dialog box appears click OK
• A new curves window appears

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Lightness Adjustments

• Modifying the placement and or shape of the line
  makes the adjustments
• There are control points at either end of the
  line. Open circles are inactive control points
  which become black when active.
• To add control points click on line
• Pointing to control point/ Click and hold and
  move changes point placement
• To remove a control point click to make the
  point active (black) and hit the delete key

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On To Color Adjustments

• Remember these changes are made to the Curves
  layer. This layer adjust the layer just beneath
  the Curves layer. In this case the Background
  copy layer. The background layer remains
  unchanged
• Within the curves window click on the Channel
  drop down. (just above the curve graph) and
  choose a channel

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Color Adjustment Good stuff

• With the a channel selected
• Modify the curve shape as desiredFor this
  example a simple slope changeTop control point
  moved to the leftBottom control point moved to
  the right
• Center stays dead center offsetting the center
  introduces color shift which is good or bad
  depending on the image

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Color Adjust b curve

• The b curve is selected from the channels drop
  down just above the graph
• Adjustments are made just like the a channel.
• Note b channel often needs to be steeper than
  the a channel but not always. Also in some
  occasions where you have color saturation maxed
  out you can flatten the curve

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Image Sharpening in Lab

• Since Lab has the Lightness isolated from the
  color info color sharpening in Lab can be
  performed without increasing color noise
• To start click OK to close the curves dialog
  window
• Click on the Layers tab to exit the channels
  display.
• Click on the Background copy Layer to make it
  active (Blue)

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Sharpening using Unsharp Mask

• With the Background copy layer active
• Click on the Channels Tab
• Click on the Lightness channel to make this
  single channel active (blue) image BW
• Click on the Filter menu at top of screen
• Point to Sharpen a flyout menu appears and
  select Unsharp Mask
• The Unsharp Mask dialog window appears

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Unsharp Mask Setting

• Threshold 0 to 6 are generally appropriate
• Radius 1 to 3 good starting value
• Amount 50 to 200 good starting value
• For this exampleThreshold 6Radius
  1Amount 150

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Reducing Color Noise

• Click on the Lab channel to review image
• To eliminate color noise click on the a channel
  to make it active (blue).
• Click on the Filter menu item at top of screen,
  point at Blur which opens flyout menu and click
  on Gaussian Blur

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Color Noise Removal

• The Gaussian Blur dialog window will open.
• Pick a radius ranging from 1to 3 for starters
• For this example radius 2.5
• Note visually inspect for noise but usually you
  will have to wing it and see what the results are
  and possibly revisit the setting

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Color noise removal from b channel

• Repeat the process same as achannel
• Note The b channel usually has the most noise
  (blue camera pixels) and typically will require a
  higher blur setting. In some cases the scratch
  filter may be useful
• When complete click on the Lab channel to see
  the final product

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Getting Back to RGB

• Lab color space is not in common use and to
  communicate this with printers, websites, and
  other software it should be converted back to RGB
  color space.
• This conversion requires a single layer.
  Multiple layers must be flattened retaining the
  changes.
• It is a good idea to save prior to conversion
  incase something goes wrong.

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Conversion to RGB

• Click on the Layers tab at the top of the
  layers window
• 3 Layers will be visible Curves Layer has
  color and contrast Background Copy has
  sharpening and color noise removal
  changes Background this is the backup and can
  be deleted
• Right click on the Background Layer and delete

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Conversion to RGB (2)

• Click on the Layer menu item at the top of the
  screen
• Click on the Flatten Image at the bottom of the
  drop down menu
• Click on the Image menu item at the top of the
  screen
• Point at the Mode in the drop down menu
• Click on the RGB color in the flyout menu
• Progress bar indicates conversion
• Save final version
• Collect admiration, royalties, and awards

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