Transcript Photoshop Lab colorspace

Photoshop Lab colorspace
A quick and easy 26 step process for
enhancing your photos
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 )
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
Slicing and Dicing in Lab
Easy powerful adjustments
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
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
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 (B&W)
a - a channel – Red Green color info
b - b channel – Blue Yellow color info
Seclection of a channel to view
• Click on the “Lightness” channel (blue area)
• Only that channel is highlighted (blue)
• The image is now B&W showing the
“Lightness” info.
• Note: The image of the a and b channels is not
very interesting that is apparently normal
To Adjust Contrast & Brightness
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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
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
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
Color Adjustment – Good stuff
• With the “a” channel selected
• Modify the curve shape as desired
For this example a simple slope change
Top control point moved to the left
Bottom 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
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
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)
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 B&W
• 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
Unsharp Mask Setting
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Threshold – 0 to 6 are generally appropriate
Radius – 1 to 3 good starting value
Amount – 50 to 200 good starting value
For this example
Threshold = 6
Radius = 1
Amount = 150
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”
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
Color noise removal from “b”
channel
• Repeat the process same as “a”channel
• 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
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.
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
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