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In the Channel Mixer, you can select a single channel by choosing a colour model and zeroing the unwanted channels. eg. for red channel, use RGB model, select to Greens and zero Green, then select Blues and zero Blue.

I can do this for RGB and CMYK. But in LAB, if I zero AOpponent and BOpponent I'm getting a blue/cyan result. What am I doing wrong? Should it not be b/w?

ps. I can separate channels by changing document colour model and clearing in the Channels panel, but I'd just like to be able to do it in Channel Mixer.


Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast Photo with i7-3770 + 16Gb RAM + Philips 40in 4K; Surface Pro 4 i5

Favourite word: Aha. For me and for others.

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In the Channels studio (you called it the channel mixer) there is the top set of Composite channels (Lightness, AOpponent, BOpponent and Alpha) below that is the set of channels for what ever layer you have selected. I choose the layer I want the B&W Lightness of and right click on the <layer name> Lightness channel and choose Create greyscale layer.

You must choose a Layer in the Layer's studio first. If necessary you may have to flatten or merge the correct set of layers to get what you want.


MacBook Pro (13-inch, Mid 2012) Mac OS 10.12.6 || Mac Pro (Late 2013) Mac OS 10.14.5

Affinity Designer 1.6.1 | Affinity Photo 1.6.7 | Affinity Publisher beta 1.7.0.337 | Affinity Photo beta 1.7.0.128 | Affinity Designer Beta 1.7.0.12

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8 hours ago, dmstraker said:

In the Channel Mixer, you can select a single channel by choosing a colour model and zeroing the unwanted channels. eg. for red channel, use RGB model, select to Greens and zero Green, then select Blues and zero Blue.

I can do this for RGB and CMYK. But in LAB, if I zero AOpponent and BOpponent I'm getting a blue/cyan result. What am I doing wrong? Should it not be b/w?

ps. I can separate channels by changing document colour model and clearing in the Channels panel, but I'd just like to be able to do it in Channel Mixer.

In Channel Mixer, you need to zero the A and B channels and offset each of them by +50% so the result is 50% of max in these channels.

To do the same with Curves, use a horizontal line at 50% of max in both A and B.

To do the same with Levels in 1.7 beta, set output black level and output white level to 50% in both A and B.

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3 hours ago, Old Bruce said:

In the Channels studio (you called it the channel mixer)...

Dave is asking about the Channel Mixer adjustment and not the Channels panel.

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2 hours ago, >|< said:

Dave is asking about the Channel Mixer adjustment and not the Channels panel.

Thanks for setting me straight and correctly answering his question.


MacBook Pro (13-inch, Mid 2012) Mac OS 10.12.6 || Mac Pro (Late 2013) Mac OS 10.14.5

Affinity Designer 1.6.1 | Affinity Photo 1.6.7 | Affinity Publisher beta 1.7.0.337 | Affinity Photo beta 1.7.0.128 | Affinity Designer Beta 1.7.0.12

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On 3/12/2019 at 7:15 PM, >|< said:

In Channel Mixer, you need to zero the A and B channels and offset each of them by +50% so the result is 50% of max in these channels.

To do the same with Curves, use a horizontal line at 50% of max in both A and B.

To do the same with Levels in 1.7 beta, set output black level and output white level to 50% in both A and B.

Oh, I get it -- rather than blank the non-required channel, push it to 50% grey.

Then L layer on top Luminosity blend. A layer in middle to Overlay blend.

Cheers!

 


Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast Photo with i7-3770 + 16Gb RAM + Philips 40in 4K; Surface Pro 4 i5

Favourite word: Aha. For me and for others.

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