Lab Channels?

[Ian Haddow]

I have this routine in Photoshop:

 

1 Duplicate the image

2 Change the mode to LAB

3 Isolate the lightness channel

4 Copy the lightness channel and blend it with the original RGB image

 

I have tried to replicate that in AP without success. Can it be done?

[James Ritson]

Hey Ian, the best way to achieve this is to:

• Use a Channel Mixer, Curves or Levels adjustment (depending on how you want to blend). On these adjustments, you can set the colour model to CMYK or LAB if you're working in RGB (and vice versa). So you could add a Curves adjustment, switch to LAB, then tweak the Lightness curve. This method is completely non-destructive.

Alternatively, if you wanted to emulate the Photoshop approach, you could:

• Edit>Copy, then File>New From Clipboard to duplicate the image into a new document.
• Document>Colour Format>LAB to convert to LAB16.
• On the Channels panel, ignore the Composite options and find the layer channels below them (usually Background Lightness, Background AOpponent etc). Right click Lightness>Create Greyscale Layer.
• Select this greyscale layer, Edit>Copy (or CMD+C), then paste it into your original RGB document (Edit>Paste or CMD+V).

 

If you wanted the composite Lightness channel pixels (rather than the isolated greyscale channel), do the same as above, but look at Composite Lightness instead, right click it and choose Load to Pixel Selection. You can then Edit>Copy this and paste it into your original document.

 

Hope that helps!