Delete Channel in LAB

B643

I have a picture that I converted to the LAB mode in Photoshop. I get a very interesting color when I turn off the a channel. I now want to delete the a channel. When I do a simple delete command, I end up with 2 alpha channels and a BW image. Question : How to delete channels in LAB mode?

jjbong

Don't know if you can delete the A channel. What I think you want to do is eliminate its effect.

The obvious way is to fill it with 50% grey. Select the A channel. Edit->Fill->50% Grey. That should give you what you want.

I've read in other forums that 50% grey in Lab isn't really 50% grey, but depends on the gamma of your display space. In my quick test, to my eye the above procedure gave the same result as turning off the visibility of the A channel.

In case that doesn't quite do it for you, you can be more precise. Select the A channel, and do Image -> Apply Image to apply the A channel to itself in Difference mode, 100%.

Richard

jjbong wrote:

Don't know if you can delete the A channel. What I think you want to do is eliminate its effect.

The obvious way is to fill it with 50% grey. Select the A channel. Edit->Fill->50% Grey. That should give you what you want.

I've read in other forums that 50% grey in Lab isn't really 50% grey, but depends on the gamma of your display space. In my quick test, to my eye the above procedure gave the same result as turning off the visibility of the A channel.

In case that doesn't quite do it for you, you can be more precise. Select the A channel, and do Image -> Apply Image to apply the A channel to itself in Difference mode, 100%.

I think you mean exclusion mode. Difference mode would yield an entirely black A channel, which would force the pic to green.

Another way is to just add a curves adjustment layer and make the A channel a horizontal line passing through the middle point of the grid.

B643

Richard wrote:

I think you mean exclusion mode. Difference mode would yield an entirely black A channel, which would force the pic to green.

Another way is to just add a curves adjustment layer and make the A channel a horizontal line passing through the middle point of the grid.

The horizontal line through the grid was quick, simple and did the job. Thanks a lot.