Greyscale or Desaturate?

Started Aug 29, 2008 | Discussions thread
carauction
Veteran MemberPosts: 6,549
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Re: Greyscale or Desaturate?
In reply to colourgeek, Aug 30, 2008

colourgeek wrote:

There are two issues here.
One is how the printer is going to print a monochrome whether it be a
rgb greyscale or single channel file;

two, the method to build the image file into a greyscale from a
colour image.

First the printing part.

Again the driver is going to handle the print stream with the
instructions set in the driver. Which driver and printer makes all
the difference. If you have multiple black inks then there could be a
black ink only choice. In the case of the 8750 or 9180 there will be
this choice as it will be 2 or 3 grey inks, or composite.
If you use ICC profiles, they are set for rgb images only.
IF you send an image in one channel (monochrome if you like) it
cannot use ICC profiles as manufacturers don't include grey ICC
profiles even if they are technically possible.
Now if you send the said monochrome you may still see options for ICC
Colorsync or ICM but that is just telling the driver to do a simple
conversion from monotone to three equal channel rgb.
If you choose rgb or ICC workflow the printer then will try to print
it's best neutral grey according to the curves via LUTs in the
profile.
If you choose to print as greyscale then the colour info is ignored
and a built in LUT for greyscale build is used. Usually there are a
few different ones for the different surface types. These have some
colour composite in them to keep the density up and perhaps maintain
a colour bias.
If you choose black ink only , well it does just that, and uses the
available inks with power curves rather than LUTs making a gamma
adjusted grey ink only greyscale. IF the inks are fairly neutral, and
the substrate makes the inks appear neutral then all is good.

Converting to B&W in Photoshop and Lightroom.

This could be a very long subject, there are whole chapters in books
written on it.
IF you choose image> mode> grayscale you will strip out colour info and
maintain luminousity with a default mix of assumed per channel
component of rgb with their brightness coming into play.
This gives you one channel greyscale with a linear curve, not
necessarily filling a histogram. Because brightness is considered,
and maintained, it is better than simply desaturating.

If you use a layer over the rgb image and de-saturate or worse,
destructively desaturate in image> adjustments> desaturate the results
will be most often flat.
Sometimes this is nice, but you have no control over the mix of the
channels, so no way to change the look that will result.
Better is use an adjustment layer over the base rgb image, B&W. With
this adjustment layer you can tweak the look by mixing your own as
much as you like and the images stays in rgb, but the numbers in rgb
will be equal according to the eyedropper.
Before the B&W layer adjustment was here we used a channel mixer
adjustment layer, or combination of this and a Hue sat or color
balance etc to tweak away but it's not very easy to do well without
breaking up the image.

In LR it's much more fun with the play of all 8 colors in the mix of
building greyscales. On top of that you can play with the white
balance and hue for even greater effects. Whatever you do you will
have an rgb equal three channel rgb when you export. Then you just
need to know what the printer driver needs to get you the result you
need.
B&W is of course more personal than colour. Only you will know what
it is you prefer.
Getting it to print however is a workflow that you need to experiment
with to find what works the best. Even though the printers are
getting better at it, tweaks are still needed. For Epson 3800 see
Eric Chan's site. For HP 8850 and 9180, Z see mine.
For Canon I have no idea!

Thanks Neil, I have bookmarked your post.

Actually, with my HP8750 I never tried 'black ink only' except for text with my HP96 cart(pigment). Gonna compare to 'High Quality' using the HP102 three ink cart.

BTW

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