How do I discard color channels?

[Chris Strobel]

Hi, in scanning people have recommended scanning in rgb, then throwing away the red and green channels and then work only on the blue.Exactally how do you discard those channels in CS2?

Thanks!............Chris

[Kirk Gittings]

Make a duplicate of the blue channel and then drag the others into the trash icon. But usually the green channel is the best on most of the scanners I have tested.

[Marko]

Chris,

The simplest way would be to add a Channel Mixer adjustment layer, check "Monochrome" and then make Red and Green channels 0% and Blue 100%.

After you're done, you can either flatten the image or, if you want to have a safeguard, create a new composite layer on top of everything. Keyboard shortcut is Shift-Option-Command-n-e on the Mac (Shift-Ctrl-Alt-n-e). It is essentially two shortcuts - one creates new layer without confirmation and the second one stamps all visible elements into the new layer.

On the side note, Blue channel usually contains the most noise - you may want to experiment with various combinations, which is easy enough with the Channel Mixer.

[Scott Kathe]

Chris,

There are a lot of ways to do this. I only have CS but I'm sure this will work on CS2 and 3: Under Windows on your Photoshop task bar make sure Channels is selected. In the Channels palette to the right you will see an arrow (>), click on this fly out menu and scroll down and click on Split Channels. This will give you three windows with the three channels in B&W. Then go back to Windows on the task bar and select Arrange then Tile and you can look at all three channels at the same time. Then from Windows again you can select Match Zoom and Location and then you will be able to take a close up look at all three channels at the same location and magnification. Sounds complicated but it's not too bad.

Scott

[Chris Strobel]

Got it.Thanks guys!

Chris

[chris jordan]

Chris, I think you might have heard it backwards. The blue channel on most films is the noisiest and lowest quality, and the worst for making B&W prints. Green is usually best, with red being a close second, and blue a very distant third. The green and red channels each contain different information, too, the way B&W film does if you put on a green or red filter. As Marko says, the best way to mix the channels is using the channel mixer tool; that way you can try different settings-- blue at 0%, Red at 100%, green at 0%, or blue at 0%, red and green both at 50% or whatever. Just remember that the three have to add up to 100%, or the image will look too light or dark. Good luck,

~cj

[Michael Mutmansky]

Chris,

They will only have meaningfully different information if you are starting with a color source. For B&W scans, they won't have substantially different information.

In all my B&W scanning experience, the Green channel has been the best, with blue second, and red generally third. Normally, green is ever so slightly sharper, and blue has more noise, so the green channel works out to be the best.


---Michael

[chris jordan]

Oh jeez, Chris I was presuming you were shooting color film. If you are shooting B&W film, then scan it in 16-bit grayscale and don't bother with color channels at all; they are superfluous.

[Kirk Gittings]

Not true Chris in my experience with prosumer flatbeds. You can get a sharper and less noisy scan in the RGB green channel than grayscale.

[Chris Strobel]

Well I wanted to try the channel thing after reading the viewcam mag article on scanning pmk negs {which is what I'm scanning}.I guess the slysdexia in me had the blue channel mixed up with green.I spent all day yesterday playing with the different channels, and at the end of the day, at least on this one 8x10 neg, I still get the best results scanning in rgb, then using NIK Color Effects Pro B&W with tonal enhancer filter in CS2.I'm going to play with channels on some other negs this week.I found Scott's method worked well for isolating the channels, and thank you all for the tips!

[Michael Mutmansky]

Even higher-end scanners will suffer from a slight color fringing, so this holds true for them as well.

Drum scanners typically use a beam splitter, so should e mostly immune to color fringing, but I have found that even with drums, the best result will be obtained by selecting the 'best' channel rather than blending the channels together.


---Michael

[Kirk Gittings]

Would someone explain to me why using the channel mixer is superior too or faster than simply duplicating the green channel and then deleting the rest? The superior channel will never change on a given scanner. You set it up as an action and it takes one second and becomes a routine step in your workflow?

[Scott Rosenberg]

chris, test your scanner to determine which is the sharpest channel and if it's necess

this was necessary on my microtek 1800f, however, with my sprintscan 45 ultra i can specify which channel to scan in when scanning in b+w mode. no need to convert anything or dump channels.

[Henry Ambrose]

Would someone explain to me why using the channel mixer is superior too or faster than simply duplicating the green channel and then deleting the rest? The superior channel will never change on a given scanner. You set it up as an action and it takes one second and becomes a routine step in your workflow?


Its not superior unless you are scanning color film - then the channel mixer routine is a good way to get the tones you want. I think there may have been a misunderstanding earlier in the thread.

[Michael Mutmansky]

Kirk,

You can set up an action for both approaches, so there is really no difference in the end with respect to ease.

I generally don't show people the channels approach, because things can get confusing if they forget to copy the channel first, and when the channels are deleted one at a time, the remainder get converted to CMYK channels.

That seems to cause some difficulty for some people, and I have found that they can follow the process better using the channel mixer.

The channel mixer isn't superior, though, and the result is the same with both approaches.


---Michael

[Marko]

Would someone explain to me why using the channel mixer is superior too or faster than simply duplicating the green channel and then deleting the rest? The superior channel will never change on a given scanner. You set it up as an action and it takes one second and becomes a routine step in your workflow?

It is, like everything else in Photoshop, just one of the many methods for accomplishing certain tasks. This just happens to be my favourite method for channel manipulation because of its flexibility - it can be used as an adjustment layer, the settings can be saved and loaded, both live and from within an action, etc.

If you dig it, it's great, if you don't it may be cumbersome, so it is all very subjective in the end.