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articles

Weekly Chatter: Converting color to grayscale?
Wednesday September 17, 2003

Section 1: converting color to grayscale?





Software > Inside Photoshop > converting color to grayscale?







AuthorSubject: converting color to grayscale?  
Steve Peters
Posted on Tue Aug 19, 2003 11:32 PM

I know that converting a color to black and white using the channel mixer is often better that just using convert to grayscale. I have a client that says that there is no way to convert a color image and make it look as good as an image shot in black and white. So they want the photographer to shoot in black and white as well as color. So this would double my work, but of course they do not have double the money. So, I just want to confirm that, you can in deed get a black and white from a color image that will be as good as an original black and white? The black and white is going to run in the newspaper. So besides using channel mixer, any other tricks? Also, for newspaper , what should my gamma be set at in color prefs? How do I soft proof for newpaper?


Jeff Schewe
Posted on Wed Aug 20, 2003 1:15 AM

On 8/19/03 11:35 PM, "IR - Steve Peters" wrote:

> I have a client that says that there is no way to convert a color image and
> make it look as good as an image shot in black and white.

Well. . .you have an idiot for a client. . .but what else is new?

> So they want the photographer to shoot in black and white as well as color.

A fool's errand. . .absolutely no reason to shoot both color and B&W.;

> So, I just want to confirm that, you can in deed get a black and white from a
> color image that will be as good as an original black and white? The black and
> white is going to run in the newspaper.

Jeeesh. . .frigging' NEWSPAPER? And he's worried ABOUT SHOOTING IN B & W?

> So besides using channel mixer, any other tricks? Also, for newspaper , what
> should my gamma be set at in color prefs? How do I soft proof for newspaper?

Channel Mixer is hammer. . .you need a chisel. Yes, there are MUCH better
ways. . .but before I go there. . .what you need to do is go into softproof
and set greyscale up a greyscale 25% and 30% dot gain. You should also
understand that for the purpose of doing actual greyscale vs monochromatic
color (a different beast) you will need to set your greyscale working space
to a dot gain that represents newsprint. . .which is either 25% or 30% (it
may actually be worse). Go to: Color Settings >Working Space >Grey and set
it to 25% or 30%. You may need to test this with the actual paper over time.
But a 30% guess is pretty close.

Then you need to understand that this greyscale working space is ONLY to be
used when doing newsprint greyscale. Normally I would have my greyscale
space set to whatever gamma my RGB working space was; 1.8 if ColorMatch RGB
or 2.2 if Adobe RGB. If I where working on CMYK files, I would set it to
simulate the dot gain of the CMYK color space. Generally this would be a 20%
gain.

You NEED to have a firm grasp of this really before you can hope to control
what prints in newsprint.

As far as converting from RGB > Greyscale. . .well, I think there's a story
in there. . .I'll post a teaser here shortly but the full tutorial really
can't be here in the forums cause it needs screen shots. . .

Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com




Martin Evening
Posted on Wed Aug 20, 2003 2:35 AM


On Wednesday, August 20, 2003, at 05:35 am, IR - Steve Peters wrote:

> I know that converting a color to black and white using the channel
> mixer is often better that just using convert to grayscale. I have a
> client that says that there is no way to convert a color image and
> make it look as good as an image shot in black and white. So they want
> the photographer to shoot in black and white as well as color. So this
> would double my work, but of course they do not have double the money.
> So, I just want to confirm that, you can in deed get a black and white
> from a color image that will be as good as an original black and
> white? The black and white is going to run in the newspaper. So
> besides using channel mixer, any other tricks? Also, for newspaper ,
> what should my gamma be set at in color prefs? How do I soft proof for
> newpaper?

Your client is confused in their thinking. The old way of converting
images from colour to black and white required making an interneg from
a colour transparency which produced a softer image from the original
and tended to lose highlight and shadow detail. The other method was to
print from a colour negative using polychromatic black and white paper.
It was therefore preferable to shoot black and white neg film as well
as colour to avoid all the hassle and compromise in quality. With
digital there is no need to shoot black and white neg, unless you
always work in black and white.

But can you believe this? An editor of a photographic magazine recently
queried some copy, asking: "what is TR one X?" I promise you, it's true.

Martin Evening


Jeff Schewe
Posted on Wed Aug 20, 2003 2:55 AM

So, here in a nutshell (without figures, screen shots or diagrams) is my way
of converting from RGB > Greyscale.

Notice: this sounds more complicated than it is and most of the initial
steps can (and for me are) recorded as action steps for easier use.

First, open an RGB image (if working in CMYK I suggest converting back to
RGB).

Set your Greyscale Color Settings to match the gamma of the RGB image.

Duplicate the document and convert the duplicate document to "greyscale".

This will give you a base of Photoshop default Greyscale-which depending on
your working spaces is "basically"; 60% of your green channel, 30% of your
red channel and 10% of your blue channel combined in a calculations command.

Keep the RGB image open and work with both images side by side.

Next, go into your RGB channels, select & activate the green channel, select
all and copy. You have to copy paste, you can't do drag & drop.

Go back to the duplicate greyscale doc and in your layers palette, activate
the background and paste. This will paste a copy of the green channel as
greyscale layer. Rename this "Green".

This is an important concept here. . .color channel pasted as a greyscale
layer. (this is why you can't drag & drop because the channel will go to the
greyscale image as a channel-which you DON'T want)

Go back to the RGB image, select and activate the red channel & copy, go
back to the greyscale image and past this as a layer. Rename it "Red".

You could also go back and copy the blue channel, but with the exception of
doing a special logo or other tricky blue contrast manipulation, I've really
not found a lot of use for pictorials.

Here's where it gets interesting. . .you can take your RGB document and
convert it to Lab. In channels, select and activate the Lightness channel
and copy it. Go back to the greyscale image and past it in. You now have a
greyscale layer that matches the color image's luminosity. . .something you
can _NOT_ get from Channel Mixer.

At this point, the "Tech" of the conversion is done. What you need to do is
the "Art". You can vary the opacity of the various layers; green, red,
lightness. This can either be done globally using the layer opacity slider
or using local adjustments using layer masks on the layers.

Using this technique, you can do a better "panchromatic" capture of the
original scene than you could _EVER_ do with B&W; film. Once you shoot film,
you lock in the panchromatic response of the film by using various color
contrast filters like a Wratten 25 to darken skies. Not so with this
technique.

Well, guess what the red channel gives you? A wratten 29 tri-color
separation filter (note: both a Wratten 25 and 29 are sep filters. . .I
don't know which would be the closest to what a digital camera or scanner
uses).

The green channel is a green separation which would be a Wratten 58.
However, I have NO IDEA how you would shoot the same data as Lab's lightness
channel on B&W; film. . .

Using this formula you can get stunning greyscale conversions that allow
very precise color tone assignment-without EVER touching levels or curves.

Yes, at the moment, this is limited to 8 bits/channel because of the
limitation of using layers. However, a similar concept can be accomplished
even in 16 bit by using Channel Mixer and History Snapshots. That works
fine, but is trickier.

You might say this seems like a pain. . .yep, good stuff is NEVER "easy".
However, again, you can record an action to do this-all except for the layer
by layer blending of the various color/greyscale layers in the greyscale
image. Imagine "painting in" a red contrast filter for the sky and a green
contrast filter for foliage? You can be as precise and accurate with your
selections used as layer masks.

Also, you can use PhotoKit's Color to Greyscale effects to get various
color>greyscale blends right in your color image. This will give you various
color contrast adjustments returned as color layers. Useful if you want to
end up with toned B&W; monochromatic prints.

Once you get things exactly the way you want it, you can convert back to RGB

To apply color toning (another series of PhotoKit effects) or take your
greyscale document and convert it to a different greyscale space such as 20%
dot gain for magazine work or 30% dot gain (or higher) for newsprint.

There are some pointers to reproduction for newsprint. . .consider that the
lightest tone (other than paper white-if you want to call that white) you'll
EVER reproduce will be a 5%-10% dot (sometimes you can't even get a 12% or
15% dot). . .and even at 75%-85% K, you'll probably not have any detail
left-it'll all turn into a deep mush. So, try to get your "good stuff" in
the 10%-75% area and maintain a real open look. Use Photoshop's softproofing
to see what you need to do to adjust for the bad paper and printing.

Any questions?

Is this something you'll would like to see in an article?

I also have some tricks for getting real even toned & colored greyscale
prints from Epson (without using Image Print-which does a great job on
neutrality but is limited to the toning effects)

Interested?


Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com






Ian Lyons
Posted on Wed Aug 20, 2003 3:03 AM

.Jeff,



>Interested?


I think that's why folk signed up for IR - i.e. material they couldn't get elsewhere! If you produced those articles the bunnies would be happy with the price of entry ;-)




Jeff Schewe
Posted on Wed Aug 20, 2003 3:15 AM

Ian Lyons wrote:

> bunnies would be happy

Hey, who are you calling a bunny. . . pilgrim?
:::written in my best John Wayne voice:::



Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com





Juanje Luzardo
Posted on Wed Aug 20, 2003 4:00 AM

Great technique, Jeff!

> Set your Greyscale Color Settings to match the gamma of the RGB image.
>

What is the point of this step? My working space is AdobeRGB and my
work go mostly to Euro coated papers. Do you suggest to use a "2.2 gray
gamma" (actually i work with "Dot Gain 15%")?


> I also have some tricks for getting real even toned & colored greyscale
> prints from Epson (without using Image Print-which does a great job on
> neutrality but is limited to the toning effects)
>
> Interested?

Jeff, you write, write... we read ; )


Barry Toon
Posted on Wed Aug 20, 2003 6:55 AM

> I also have some tricks for getting real even toned & colored greyscale
> prints from Epson (without using Image Print-which does a great job on
> neutrality but is limited to the toning effects)
>
> Interested?

Jeff, you write, this one definitely reads! Wrattens with undos, GREAT!


Jeff Schewe
Posted on Wed Aug 20, 2003 10:30 AM

Juanje Luzardo wrote:

> What is the point of this step? My working space is AdobeRGB and my
> work go mostly to Euro coated papers. Do you suggest to use a "2.2 gray
> gamma" (actually i work with "Dot Gain 15%")?

Since you are doing a copy/paste from an image whose gamma is 2.2 (the color
image), you need to match the gamma in the greyscale document. At least for
the period of time it takes to copy the channels over. Once done, you can to
a conversion from greyscale gamma to greyscale dot gain.

If you don't, and you have the greyscale copy converted to a greyscale dot
gain instead of matching gamma, the copy/paste won't be converted from gamma
to dot gain. So, you'll be pasting a gamma greyscale into a dot gain
layers-resulting in incorrect data.

The Photoshop engineers didn't figure people would be doing this so they
didn't attach a convert on paste warning for this. We users sometimes behave
in "unexpected behavior".

:-)


Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com





Ian Lyons
Posted on Wed Aug 20, 2003 10:54 AM

>The Photoshop engineers didn't figure people would be doing this so they
didn't attach a convert on paste warning for this. We users sometimes behave
in "unexpected behavior".


Are you going to use your influence to make sure we get it next time round?


Jeff Schewe
Posted on Wed Aug 20, 2003 11:15 AM

Ian Lyons wrote:

> Are you going to use your influence to make sure we get it next time round?

That's a hill I ain't willing to die on. . .and besides, it's too late (as
you know full well)

:-)


Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com





John MacLean
Posted on Wed Aug 20, 2003 12:03 PM

how bout this?:

www.russellbrown.com/tips/moviesps/ColortoB&W.mov;


John MacLean
Posted on Wed Aug 20, 2003 12:04 PM

PS - why does the forum truncate URL's?


Ian Lyons
Posted on Wed Aug 20, 2003 12:11 PM


> Jeff Schewe wrote:
>
> That's a hill I ain't willing to die on. . .and besides, it's too late (as
> you know full well)
>
> :-)


I'm sayin nuttin! ;-)=




Jeff Schewe
Posted on Wed Aug 20, 2003 12:20 PM

John MacLean wrote:

> how bout this?:
>
> www.russellbrown.com/tips/moviesps/ColortoB&W.mov;

It's a fun and useful technique, but limited. . .

The big problem with this approach is that in doing the underlying Hue & Sat
adjustment to vary the B&W; conversion you are actually doing an image
adjustment that can degrade the image. If you push Russell's approach too
far, the image will posterize. . .

It makes for a great demo. . .but a less controllable conversion than using
the actual RGB channels (and, there's no way of actually using the Lab
version of the image).


Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com




Corey Rusk
Posted on Wed Aug 20, 2003 12:34 PM

> Jeff Schewe wrote:

>Is this something you'll would like to see in an article?

YES!

>I also have some tricks for getting real even toned & colored greyscale
>prints from Epson (without using Image Print-which does a great job on
>neutrality but is limited to the toning effects)

>Interested?

YES!


Andrew Rodney
Posted on Wed Aug 20, 2003 12:50 PM

on 8/20/03 11:05 AM, IR - John MacLean wrote:

> how bout this?:
>
> www.russellbrown.com/tips/moviesps/ColortoB&W.mov;

I like it. I know Jeff prefers other methods and both have merit (Russell's
for ease of use and the ability to really see what you're doing). I've had
very good results with it and find the lesser power user (The Schewe's of
the Photoshop world) dig it. I can use this technique and take a 24 patch
ColorChecker and make every square separate from the other in nothing flat.


Steve Peters
Posted on Wed Aug 20, 2003 3:55 PM

Jeff,
This is exactly what I was lookong for. So if I am using Adobe RGB, I want to set my gray gamma to 2.2 wile i am draging channels over. Once I am done with that, then I need to convert to a dot gain of 30% for newsprint? Is this dot gain somthing that I should be able to ask a print producer about, to make sure that I am using the right dot gain for a particular newspaper, or do they all typicaly have about a 30% dot gain?
Thanks again,
Steve


Jeff Schewe
Posted on Wed Aug 20, 2003 4:25 PM

Steve Peters wrote:

> This is exactly what I was lookong for. So if I am using Adobe RGB, I want to
> set my gray gamma to 2.2 while i am draging channels over.

Well, aside form the fact you have to actually copy/paste since drag & drop
doesn't work. . .but yes.

> Once I am done with that, then I need to convert to a dot gain of 30% for
> newsprint?

Yep. . .

> Is this dot gain somthing that I should be able to ask a print
> producer about, to make sure that I am using the right dot gain for a
> particular newspaper, or do they all typicaly have about a 30% dot gain?

You can TRY to ask but the odds are you will not receive a comprehensible
response. . .30% is a reasonable guess, but like I said, it could be better,
it could be worse. Newsprint is all over the map.

In addition to the obvious toning and prep, you also need to worry about
high quality sharpening. The worse the reproduction the more critical
sharpening becomes. . .but that's another topic please :-)


Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com





Bruce Fraser
Posted on Wed Aug 20, 2003 4:35 PM

In my experience, 30% is optimistic for most newsprint in the US. I've encountered pubs with more dot gain than Photoshop used to be able to handle (it didn't let you enter anything higher than 40%).

Bear in mind that the first thing the average newsprint press op does is to crank up the black ink until the type is nice and fat. That can drive the dot gain ballistic.

Also, newsprint presses aren't noted for their consistency. When in doubt, err on the side of less contrast rather than more, and don't expect to able to reliably produce dots smaller than 7�8%.


Cathy Brown
Posted on Wed Aug 20, 2003 10:19 PM

Another "YES!!!" for the article!


Geoffrey Byers
Posted on Fri Aug 22, 2003 11:54 PM

> So, here in a nutshell (without figures, screen shots or diagrams) is my way
> of converting from RGB > Greyscale.
>.............
> Next, go into your RGB channels, select & activate the green channel, select
> all and copy. You have to copy paste, you can't do drag & drop.
>
> Go back to the duplicate greyscale doc and in your layers palette, activate
> the background and paste. This will paste a copy of the green channel as
> greyscale layer. Rename this "Green".
>
>...............
>
> Jeff Schewe
> www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com


I think you mean: �Load the green channel as a selection, copy the selection, and paste as a new layer in the greyscale document�.�, but I could be wrong. If you just copy all and paste as a new layer, it obviously just becomes 100% of the visible document.

Geoff


Jeff Schewe
Posted on Sat Aug 23, 2003 12:45 AM

Geoffrey Byers wrote:

> I think you mean: Load the green channel as a selection, copy the selection,
> and paste as a new layer in the greyscale document, but I could be wrong.
> If you just copy all and paste as anew layer, it obviously just becomes 100%
> of the visible document.

Nope, you copy. . .then you can vary the opacity either globally or locally
via a layer mask. Loading the green channel only creates a selection. . .you
want the green pixel data, not a selection.

You'll see. . .

Jeff Schewe
www.schewephoto.com - www.pixelgenius.com - www.imagingrevue.com






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