Apply Image Vs Copy Channel

pack_tor

Hi Guys,

I'm noticing something strange. Would appreciate greatly if someone can point out what I'm missing...

I apply the any channel (e.g green) onto a separate layer (using apply image command), in effect producing a greyscale image. I notice that if I do this, this layer is generally slightly darker than the original green channel. If do a copy of the green channel to a separate layer (ctrl+2, ctrl+a, ctrl+c, ctrl+~, ctrl+v) , it is lighter. If I do the difference between the apply image layer and the copied layer (difference blend mode), I see minute differences in luminosity (while there should be no differences)

If I do exactly the same thing on a different computer, everything seems ok. It almost seems like it's an issue with a setting.

My brain has frozen now... could anybody please help?

jjbong

pack_tor wrote:

Hi Guys,

I'm noticing something strange. Would appreciate greatly if someone can point out what I'm missing...

I couldn't reproduce the behavior you described. I'd suggest the checking the obvious on Apply Image: set to Normal, Background (not Merged). Make sure that when you do the difference, only the Green channel is selected.

Copy channel is more foolproof, as it has fewer settings. This suggests that the problem is in the difference display (again, maybe you've got RGB selected instead of just Green).

I hope this helps.

Richard

pack_tor wrote:

Hi Guys,

I'm noticing something strange. Would appreciate greatly if someone can point out what I'm missing...

I apply the any channel (e.g green) onto a separate layer (using apply image command), in effect producing a greyscale image. I notice that if I do this, this layer is generally slightly darker than the original green channel. If do a copy of the green channel to a separate layer (ctrl+2, ctrl+a, ctrl+c, ctrl+~, ctrl+v) , it is lighter. If I do the difference between the apply image layer and the copied layer (difference blend mode), I see minute differences in luminosity (while there should be no differences)

If I do exactly the same thing on a different computer, everything seems ok. It almost seems like it's an issue with a setting.

My brain has frozen now... could anybody please help?

Are you doing the comparison at 100% size? PS does some weird stuff with smaller sized previews.

BinaryFx

When Photoshop displays a single channel - whether this is a true grayscale mode file with only one channel or a single channel of an RGB file - it will use the Grayscale working space in Colour Settings to display the visual appearance/density, rather than the document gamma/dot gain setting.

If your grayscale WS is set to say 20% dot gain, then this will display a different density, for the single RGB channel, rather than displaying the single channel in the same gamma as the RGB working space. It would be better if Photoshop was smart enough to display a single channel in the appropriate colour modes gamma/dot gain, rather than simply using a sinlge setting.

I am pretty sure that if you were working with say 2.2 gamma RGB data and had your Grayscale WS set to 2.2 gamma in colour settings - that you would not see two different tonal densities.


Hope this helps,

Stephen Marsh
http://members.ozemail.com.au/~binaryfx/

jjbong

BinaryFx wrote:

When Photoshop displays a single channel - whether this is a true gray scale mode file with only one channel or a single channel of an RGB file - it will use the Grayscale working space in Colour Settings to display the visual appearance/density, rather than the document gamma/dot gain setting.

So then the question is, are the differences uniformly lighter or darker (that is, are you getting almost-black instead of completely-black), or do you see luminosity differences that vary over the image?

pak_tor, can you answer this?

Stephen, if the result is not uniform, that is, if the results are spots of difference in the image, I don't see how the gamma of the default Greyscale could produce this. If they are uniform, then definitely yes.

I found I could reproduce the behavior if I had RGB selected instead of just the G channel.