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Increase in saturation can DECREASE contrast (gurus refuted)

 
 
David Virgil Hobbs
Guest
Posts: n/a
 
      12-29-2006
It is mind-boggling, judging from the opinions presented on the
internet, the lack of understanding regarding color saturation in
photography. Most of the so-called experts seem to be mindlessly
reciting mantras they have heard somewhere without understanding the
topic. They all self-confidently proclaim that an increase in
saturation INCREASES contrast.

In reality, when two colors are similar in that in both colors the same
element of the RGB (red-green-blue) components dominates, an increase
in saturation DECREASES contrast between the two colors; but when two
colors are dissimilar in that in one color one element of the RGB
dominates while in the other color another element of the RGB
dominates, an increase in saturation INCREASES contrast between the two
colors. This is important because so many photos of persons are wrecked
by an excess of contrast between two similar colors such as on a
person's face.

In digital photography colors are composed of a mix of R for red, G for
green, and B for blue values. I here prove to you that when two colors
both feature the R value being dominant, or when two colors both
feature the G value being dominant, or when two colors both feature the
B value being dominant, an increase in saturation results in a
DECREASE, not an INCREASE in contrast between the two colors; and when
two colors feature in one color one of the rgb values being dominant
and in the other color another of the rgb values being dominant then
saturation INCREASES contrast between the two colors.

All except one of the definitions of saturation I found on the internet
I found to be incomprehensible; they all sounded as if someone was
reciting a mantra he had memorized that he did not understand. The
definition I found to be comprehensible was:

"What is saturation, and why it is so important?
The saturation defines the level of pureness or a color. All the colors
derives by a mix of the tree primary colors - red, yellow and blue (or
Red, Green and Blue in the common RGB color space). The more a color
is saturate, the more it is close the one of the primary colors :
theoretically, if you raise the saturation to its upper limit the photo
would be composed by just red, green and blue."
-- http://www.juzaphoto.com/eng/article...management.htm

>From my personal experience I have seen how an increase in saturation

makes a color in which the R value is dominant more red. From working
with HTML I have seen what the photography gurus seem to fail to
understand, which is that in shades of gray, the R G and B values are
equal. The photography gurus all agree that as saturation is decreased
the colors draw closer to being shades of gray as you can see working
with saturation in a photo editor.

Thus when there is zero saturation, or shades of gray, that means that
in each color, the difference between r and g and b, is zero, ie
rgb(192, 192, 192), rgb(127, 127, 127), rgb(67, 67, 67). This means
(my personal inference) that as saturation is decreased, the
differences in the r and the g and the b in the color decrease as the r
g and b values all draw closer to an average of the r and the g and the
b values in the color.

As saturation is increased, the difference between the r g or b element
that is strongest in the color and the other colors in the RGB trinity
is increased, as I can tell from my own personal experience and from
the quotation from www.juzaphoto.com included above.

Thus, an increase in saturation will DECREASE the contrast between two
colors both of which have say the R component amongst r g and b
dominating the g and b components; and an increase in saturation will
increase the contrast between two colors when one color has say the r
component dominating the g and b components, and the other color has
say the b component dominating the r and g components.

Take for example two colors found in a man's face. One is
rgb(210,131,11; the other is rgb(233,164,135). In both colors the r
dominates. The difference between the r's is 23, between the g's is 33,
between the b's is 17 for a total differential of 73. If, increasing
saturation, you push the r's half way to the maximum 255, and the g's
and the b's half way to the minimum of 0, you end up with the first
color being 232,65,59 and the second color being 244, 82, 67 so that
the difference between the colors has declined from 73 to 37, a
decrease in contrast. Check out what these colors look like in even a
simple program the internet gurus are too good for such as Microsoft
Paint and you can see the decline in contrast with your own eyes.

Again, take for example two numbers 249 and 55; the difference between
the two is 194. Push 249 half way to 255 and you get 252, push 55 half
way to 255 and you get 155; the difference between the two numbers
declines from 194 to only 97.

Yet again, take for example two numbers 150 and 100; the difference
between the two is 50. Push 150 half way to 255 and you get 202, push
100 half way to 255 and you get 177; the difference between the two
numbers declines from 50 to only 25.

Now take two colors, with one featuring the R or red component
dominating the G and B components, and the other featuring the B or
blue component dominating the R and G components, say rgb(210,131,11
and rgb(55,85,121). The difference between the r's is 155, between the
g's is 46, and between the b's is 3, for a total differential of 204.
If you increase saturation pushing the first color's dominating r value
half way to 255 and the first color's g and b values half way to zero
you change the first color to 232,65,59. If you increase saturation
pushing the second color's dominating b or blue value half way to 255
and the second color's r and g values half way to zero, the second
color changes to 27,42,188. The overall differential between the two
colors becomes 205 in the r's, 23 in the g's, and 129 in the b's for a
total of 357, whereas previously the total differential was only 204,
and the contrast INCREASES instead of decreases because in this case in
one color the R value dominates and in the other color the B value
dominates.

I find it significant and incredible that the digital photography world
has apparently failed to understand this key point, that increasing
saturation decreases contrast between two similar colors while
increasing contrast between two dissimilar colors.

Many of my photos of humans were unacceptable using a digital camera
that a short while ago sold for $600 but now sells for only $100 (I
wonder why?)--until I cured the hyper-contrast in the faces of the
subjects by increasing saturation and then brought the tint back to
normal. Using said camera, my photos of a person would make the person
look like a different person from photo to photo. Photos of humans can
be wrecked by hyper-contrast between two similar colors in a person's
face resulting from a lack of saturation, but all you ever hear from
the internet photography gurus is that increasing saturation INCREASES
contrast.

I confess to being proud that I, an amateur dabbler, have been able to
figure out how a lack of saturation can result in hyper-contrast,
without any help from anyone, so as to put down the photography gurus
who proclaim that increasing saturation increases contrast. Too bad
employers are so mindlessly concerned with credentials, experience, and
coddling those whom the rude label as 'dorks', that they de-emphasize
all kinds of important qualities and--since hyper-emphasis of one thing
leads to de-emphasis of other things--under-value persons such as
myself.


@2006 David Virgil Hobbs
http://www.angelfire.com/vincemoon

 
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Pat
Guest
Posts: n/a
 
      12-29-2006
Did someone get up on the wrong side of the bed this morning. You are
ranting against a non-problem. To start with, I don't remember "all"
of those experts going on as you said. If I did see it, it went in one
eye and out the other because I don't necessarily believe everything I
read. Contracts, saturation, everything is sort of picture-specific.
That's why you have the ability to adjust it by hand. Sometimes I up
it. Sometimes I lower it. It all depends. So go have another cup of
coffee and calm down.


David Virgil Hobbs wrote:
> It is mind-boggling, judging from the opinions presented on the
> internet, the lack of understanding regarding color saturation in
> photography. Most of the so-called experts seem to be mindlessly
> reciting mantras they have heard somewhere without understanding the
> topic. They all self-confidently proclaim that an increase in
> saturation INCREASES contrast.
>
> In reality, when two colors are similar in that in both colors the same
> element of the RGB (red-green-blue) components dominates, an increase
> in saturation DECREASES contrast between the two colors; but when two
> colors are dissimilar in that in one color one element of the RGB
> dominates while in the other color another element of the RGB
> dominates, an increase in saturation INCREASES contrast between the two
> colors. This is important because so many photos of persons are wrecked
> by an excess of contrast between two similar colors such as on a
> person's face.
>
> In digital photography colors are composed of a mix of R for red, G for
> green, and B for blue values. I here prove to you that when two colors
> both feature the R value being dominant, or when two colors both
> feature the G value being dominant, or when two colors both feature the
> B value being dominant, an increase in saturation results in a
> DECREASE, not an INCREASE in contrast between the two colors; and when
> two colors feature in one color one of the rgb values being dominant
> and in the other color another of the rgb values being dominant then
> saturation INCREASES contrast between the two colors.
>
> All except one of the definitions of saturation I found on the internet
> I found to be incomprehensible; they all sounded as if someone was
> reciting a mantra he had memorized that he did not understand. The
> definition I found to be comprehensible was:
>
> "What is saturation, and why it is so important?
> The saturation defines the level of pureness or a color. All the colors
> derives by a mix of the tree primary colors - red, yellow and blue (or
> Red, Green and Blue in the common RGB color space). The more a color
> is saturate, the more it is close the one of the primary colors :
> theoretically, if you raise the saturation to its upper limit the photo
> would be composed by just red, green and blue."
> -- http://www.juzaphoto.com/eng/article...management.htm
>
> >From my personal experience I have seen how an increase in saturation

> makes a color in which the R value is dominant more red. From working
> with HTML I have seen what the photography gurus seem to fail to
> understand, which is that in shades of gray, the R G and B values are
> equal. The photography gurus all agree that as saturation is decreased
> the colors draw closer to being shades of gray as you can see working
> with saturation in a photo editor.
>
> Thus when there is zero saturation, or shades of gray, that means that
> in each color, the difference between r and g and b, is zero, ie
> rgb(192, 192, 192), rgb(127, 127, 127), rgb(67, 67, 67). This means
> (my personal inference) that as saturation is decreased, the
> differences in the r and the g and the b in the color decrease as the r
> g and b values all draw closer to an average of the r and the g and the
> b values in the color.
>
> As saturation is increased, the difference between the r g or b element
> that is strongest in the color and the other colors in the RGB trinity
> is increased, as I can tell from my own personal experience and from
> the quotation from www.juzaphoto.com included above.
>
> Thus, an increase in saturation will DECREASE the contrast between two
> colors both of which have say the R component amongst r g and b
> dominating the g and b components; and an increase in saturation will
> increase the contrast between two colors when one color has say the r
> component dominating the g and b components, and the other color has
> say the b component dominating the r and g components.
>
> Take for example two colors found in a man's face. One is
> rgb(210,131,11; the other is rgb(233,164,135). In both colors the r
> dominates. The difference between the r's is 23, between the g's is 33,
> between the b's is 17 for a total differential of 73. If, increasing
> saturation, you push the r's half way to the maximum 255, and the g's
> and the b's half way to the minimum of 0, you end up with the first
> color being 232,65,59 and the second color being 244, 82, 67 so that
> the difference between the colors has declined from 73 to 37, a
> decrease in contrast. Check out what these colors look like in even a
> simple program the internet gurus are too good for such as Microsoft
> Paint and you can see the decline in contrast with your own eyes.
>
> Again, take for example two numbers 249 and 55; the difference between
> the two is 194. Push 249 half way to 255 and you get 252, push 55 half
> way to 255 and you get 155; the difference between the two numbers
> declines from 194 to only 97.
>
> Yet again, take for example two numbers 150 and 100; the difference
> between the two is 50. Push 150 half way to 255 and you get 202, push
> 100 half way to 255 and you get 177; the difference between the two
> numbers declines from 50 to only 25.
>
> Now take two colors, with one featuring the R or red component
> dominating the G and B components, and the other featuring the B or
> blue component dominating the R and G components, say rgb(210,131,11
> and rgb(55,85,121). The difference between the r's is 155, between the
> g's is 46, and between the b's is 3, for a total differential of 204.
> If you increase saturation pushing the first color's dominating r value
> half way to 255 and the first color's g and b values half way to zero
> you change the first color to 232,65,59. If you increase saturation
> pushing the second color's dominating b or blue value half way to 255
> and the second color's r and g values half way to zero, the second
> color changes to 27,42,188. The overall differential between the two
> colors becomes 205 in the r's, 23 in the g's, and 129 in the b's for a
> total of 357, whereas previously the total differential was only 204,
> and the contrast INCREASES instead of decreases because in this case in
> one color the R value dominates and in the other color the B value
> dominates.
>
> I find it significant and incredible that the digital photography world
> has apparently failed to understand this key point, that increasing
> saturation decreases contrast between two similar colors while
> increasing contrast between two dissimilar colors.
>
> Many of my photos of humans were unacceptable using a digital camera
> that a short while ago sold for $600 but now sells for only $100 (I
> wonder why?)--until I cured the hyper-contrast in the faces of the
> subjects by increasing saturation and then brought the tint back to
> normal. Using said camera, my photos of a person would make the

person
> look like a different person from photo to photo. Photos of humans

can
> be wrecked by hyper-contrast between two similar colors in a

person's
> face resulting from a lack of saturation, but all you ever hear from
> the internet photography gurus is that increasing saturation

INCREASES
> contrast.


If many of the pictures were unacceptable, it shouldn't have taken you
long to figure out how to adjust you camera to make them acceptable.
Most cameras allow you to adjust contract and saturation inside the
camera. They do that for a reason, ya know. And maybe you shouldn't
be using a $100 camera

Again, who are these "internet photography gurus".

And just because their theory doesn't work for your particular
circumstance doesn't mean it doesn't work for most people most of the
time.

>
> I confess to being proud that I, an amateur dabbler, have been able to
> figure out how a lack of saturation can result in hyper-contrast,
> without any help from anyone, so as to put down the photography gurus
> who proclaim that increasing saturation increases contrast. Too bad
> employers are so mindlessly concerned with credentials, experience, and
> coddling those whom the rude label as 'dorks', that they de-emphasize
> all kinds of important qualities and--since hyper-emphasis of one thing
> leads to de-emphasis of other things--under-value persons such as
> myself.
>
>
> @2006 David Virgil Hobbs
> http://www.angelfire.com/vincemoon


I'm glad you got the whole saturation/contract thing figured out. Now
if you could just figure out the whole URL thing on your link so that
it works, you'd be doing good.

 
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Richard Polhill
Guest
Posts: n/a
 
      12-29-2006
David Virgil Hobbs wrote:

<snip unprovoked rant>

What brought that on?

Rich
 
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Lionel
Guest
Posts: n/a
 
      12-29-2006
On Fri, 29 Dec 2006 15:42:35 +0000, Richard Polhill
<(E-Mail Removed)> wrote:

>David Virgil Hobbs wrote:
>
><snip unprovoked rant>
>
>What brought that on?


A poorly medicated case of paranoid-schizophrenia, at a guess, seeing
as I've never even heard of any 'gurus' making claims anything like
the ones he thinks he's refuted.
(I wonder if he's the same loon who keeps on spewing all that demented
spam about claims of imaginary MI5 harrassment?)

 
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mark.thomas.7@gmail.com
Guest
Posts: n/a
 
      12-29-2006
Sorry for snipping most of that enormously long, mindless drivel, but..
it was enormously long mindless drivel...

David Virgil Hobbs wrote:
> They all self-confidently proclaim that an increase in
> saturation INCREASES contrast.


Strong words. Name the 'gurus' you refute.

> In reality, when two colors are similar in that in both colors the same
> element of the RGB (red-green-blue) components dominates, an increase
> in saturation DECREASES contrast between the two colors; but when two
> colors are dissimilar in that in one color one element of the RGB
> dominates while in the other color another element of the RGB
> dominates, an increase in saturation INCREASES contrast between the two
> colors.


Well done, Einstein! The post could have ended there.

> This is important because so many photos of persons are wrecked
> by an excess of contrast between two similar colors such as on a
> person's face.


"so many" - f'rinstance?


> All except one of the definitions of saturation I found on the internet
> I found to be incomprehensible


Maybe that was because they were right. The one you quote is horribly
flawed.

> "What is saturation, and why it is so important?
> The saturation defines the level of pureness or a color.

No. It is the intensity of the colour. 'Pureness' is a very loose
term and could simply refer to the colour's accuracy or closeness to
the original.

> All the colors
> derives (sic) by a mix of the tree (sic) primary colors - red, yellow and blue (or
> Red, Green and Blue in the common RGB color space).

Only when using the RGB model. Colors are actually defined by
different wavelengths and mixtures of wavelengths. The RGB, CMYK, LAB,
etc models are simply ways to try to represent colours using available
technology or to simulate the operation of the eye.

> The more a color
> is saturate (sic), the more it is close the (sic) one of the primary colors :
> theoretically, if you raise the saturation to its upper limit the photo
> would be composed by (sic) just red, green and blue."


I disagree strongly with this interpretation. For example, if the
colour had equal blue and green components, this definition suggests it
would have to become 'more close' to *one* primary - so it would have
to become *either* more blue or more green, in order to become more
saturated. Stupid.

> I find it significant and incredible that the digital photography world
> has apparently failed to understand this key point


'Apparently' is the key word here. It seems so to you, yet you haven't
posted a single example. And the example you post as gospel is flawed.
Maybe when the rest of the world thinks one thing, and you think
another, there could be an alternative to the thought that *you* are
the only correct one..

> Many of my photos of humans were unacceptable

Gee, really?

> ..until I cured the hyper-contrast

Which you most likely introduced, either by excessive post-processing
or bad camera settings.

> .. and then brought the tint back to normal.

Gee, again. Maybe you should ask why you *had* to bring them back to
normal?

> I confess to being proud that I, an amateur dabbler, have been able to
> figure out how a lack of saturation can result in hyper-contrast,
> without any help from anyone, so as to put down the photography gurus
> who proclaim that increasing saturation increases contrast.


Aha, there we have it - is this an attempt at an ego trip? Sorry. You
missed.

> Too bad
> employers are so mindlessly concerned with credentials, experience, and
> coddling those whom the rude label as 'dorks', that they de-emphasize
> all kinds of important qualities and--since hyper-emphasis of one thing
> leads to de-emphasis of other things--under-value persons such as
> myself.


oh.
uhuh.
umm.....

Maybe you might get a bit less 'under-valued' if you stopped slanging
off at imaginary others, waffling on forever, and making out there is a
problem when none exists. Yes, some amateurs (and pseudo pro's) aren't
very good at post processing and may screw up colours, contrast, and
skin-tones with that. Indeed if you want to see saturation and
contrast gone wrong (not many flesh tones though), try
http://www.kenrockwell.com/gallery.htm ... (O;

But no 'experts' I have seen have made any misleading claims. We
await, with breath baited, all your examples to the contrary.

(O;

PS - maybe you should fix your homepage link...

 
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twilson@thomasjwilson.ca
Guest
Posts: n/a
 
      12-30-2006
....couldn't we all just get along?

Come on everyone, there is nothing quite as entertaining as a good old
fashioned rant in a public place. It's kind of like watching a husband
and wife going three rounds in the grocery store over which brand of
jam to buy, break out the snacks, sit back and enjoy... and when said
rant gets copyrighted... whoa Daddy!

I can just see all those gurus gnashing their teeth now that they have
been so ultimately and finally refuted on that oh so topical saturation
debate! The fate of the universe may very well have been settled right
here in this very forum... take that you so called saturation experts
(shake clenched fist at retreating lab coated, bespecked experts
scrambling back under the rocks from whence they came)! The saturation
gurus are likely all down at the local bar muttering under their breath
trying to figure out how to get around that blasted copyright
statement... personally I can hardly wait for the fireworks to begin!

 
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Roger N. Clark (change username to rnclark)
Guest
Posts: n/a
 
      12-30-2006
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> David Virgil Hobbs wrote:
>>"What is saturation, and why it is so important?
>>The saturation defines the level of pureness or a color.

>
> No. It is the intensity of the colour. 'Pureness' is a very loose
> term and could simply refer to the colour's accuracy or closeness to
> the original.


A saturated color has nothing to do with the intensity if the color.
Pureness is an OK term, but could be misleading, like you point
out below. Saturation is how monochromatic the color is,
whether it be blue, blue-green, orange, etc. A laser
produces highly saturated light (e.g. a green laser, or a red laser)
As more light of different wavelengths contribute to the color,
it becomes less saturated, or less pure.
Sodium street lamps produce a nearly pure orange color,
for example. Such colors are difficult to represent with
RGB or CMYK models. The eye, with its non-linear and sometimes
negative response can make color perceptions not possible
with ink on paper, or phosphors on a CRT

>>All the colors
>>derives (sic) by a mix of the tree (sic) primary colors - red, yellow and blue (or
>>Red, Green and Blue in the common RGB color space).

>
> Only when using the RGB model. Colors are actually defined by
> different wavelengths and mixtures of wavelengths. The RGB, CMYK, LAB,
> etc models are simply ways to try to represent colours using available
> technology or to simulate the operation of the eye.


I agree.

>>The more a color
>>is saturate (sic), the more it is close the (sic) one of the primary colors :
>>theoretically, if you raise the saturation to its upper limit the photo
>>would be composed by (sic) just red, green and blue."

>
> I disagree strongly with this interpretation. For example, if the
> colour had equal blue and green components, this definition suggests it
> would have to become 'more close' to *one* primary - so it would have
> to become *either* more blue or more green, in order to become more
> saturated. Stupid.


I agree with your disagreement

>>I find it significant and incredible that the digital photography world
>>has apparently failed to understand this key point

>
> 'Apparently' is the key word here. It seems so to you, yet you haven't
> posted a single example. And the example you post as gospel is flawed.
> Maybe when the rest of the world thinks one thing, and you think
> another, there could be an alternative to the thought that *you* are
> the only correct one..


It seems to me the OP is another case of having learned enough
to start thinking ahead, but hasn't learned enough yet to
think ahead along the right path. But at least he is thinking,
which is a lot more than most people.

To the OP. I think what the OP is referring to regarding
saturation is what is called blocking up of colors. So if we
read "the experts" we will see discussion about blocking up
of colors when processing. This is not new with digital; it
was talked about in film days, and became more widely
discussed when the super saturated films came out,
like Velvia. So, to the OP, go find some books like
Real World Color Management by Fraser et al.

Roger
 
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acl
Guest
Posts: n/a
 
      12-30-2006
Roger N. Clark (change username to rnclark) wrote:
> It seems to me the OP is another case of having learned enough
> to start thinking ahead, but hasn't learned enough yet to
> think ahead along the right path. But at least he is thinking,
> which is a lot more than most people.
>


I completely agree. On the other hand, and in my experience, there are
2 kinds of people who do this (try to progress their understanding by
thinking ahead): Those who only think ahead, disregarding anything else
they might be told (ie their received knowledge stays at the level it
was when they started thinking), and those who keep listening and judge
what they are told before accepting or rejecting it (or recreating it
for themselves, same thing).

The difference between these two is even more obvious on usenet than in
reality. Personally (I emphasise this personally, YMMV), the problem I
have with those of the first type is that I almost always end up having
long and stupid arguments with them (in reality; on usenet I try to
avoid it, none too succesfully I may add), and of course how can you
argue with someone who simply refuses to even consider anything he
hasn't thought of himself? It is a total waste of time. I'd be a
happier man (and one with a lower blood pressure) if most people just
ignored technical stuff (or more accurately, if I ignored such people.
and avoided posting such rants as this).

> To the OP. I think what the OP is referring to regarding
> saturation is what is called blocking up of colors. So if we
> read "the experts" we will see discussion about blocking up
> of colors when processing. This is not new with digital; it
> was talked about in film days, and became more widely
> discussed when the super saturated films came out,
> like Velvia. So, to the OP, go find some books like
> Real World Color Management by Fraser et al.


Yes, that is what it sounds like. But I don't think it is all that
complicated to avoid this blocking up (which is what he seems to want
to do), you just play with various controls of your image editing
program, experiment with your printer, and evertually you'll get an
intuitive understanding of what is going on (unless you go bankrupt
buying inks first.

 
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Roger N. Clark (change username to rnclark)
Guest
Posts: n/a
 
      12-31-2006
acl wrote:
> Roger N. Clark (change username to rnclark) wrote:
>
>>It seems to me the OP is another case of having learned enough
>>to start thinking ahead, but hasn't learned enough yet to
>>think ahead along the right path. But at least he is thinking,
>>which is a lot more than most people.

>
> I completely agree. On the other hand, and in my experience, there are
> 2 kinds of people who do this (try to progress their understanding by
> thinking ahead): Those who only think ahead, disregarding anything else
> they might be told (ie their received knowledge stays at the level it
> was when they started thinking), and those who keep listening and judge
> what they are told before accepting or rejecting it (or recreating it
> for themselves, same thing).
>
> The difference between these two is even more obvious on usenet than in
> reality. Personally (I emphasise this personally, YMMV), the problem I
> have with those of the first type is that I almost always end up having
> long and stupid arguments with them (in reality; on usenet I try to
> avoid it, none too succesfully I may add), and of course how can you
> argue with someone who simply refuses to even consider anything he
> hasn't thought of himself? It is a total waste of time. I'd be a
> happier man (and one with a lower blood pressure) if most people just
> ignored technical stuff (or more accurately, if I ignored such people.
> and avoided posting such rants as this).


Yeah, I agree too.

>>To the OP. I think what the OP is referring to regarding
>>saturation is what is called blocking up of colors. So if we
>>read "the experts" we will see discussion about blocking up
>>of colors when processing. This is not new with digital; it
>>was talked about in film days, and became more widely
>>discussed when the super saturated films came out,
>>like Velvia. So, to the OP, go find some books like
>>Real World Color Management by Fraser et al.

>
> Yes, that is what it sounds like. But I don't think it is all that
> complicated to avoid this blocking up (which is what he seems to want
> to do), you just play with various controls of your image editing
> program, experiment with your printer, and evertually you'll get an
> intuitive understanding of what is going on (unless you go bankrupt
> buying inks first.


There is a "trick" to recovering detail in blocked up colors
convert to CMYK space and feather select the blocked-up areas
then select the channel color opposite what was blocked-up, and change
the contrast on that channel. For example, if the blocked up
color is red (e.g. a red flower), convert to CMYK (best if
your data are 16-bit), select the cyan (C) channel and put a
selection around the flower. Cyan is blue + green so doesn't
have red. Change the contrast with the curves tool of the flower
in that channel. (In Photoshop always use levels or curves to
change contrast, not the contrast tool. The contrast tool is
an additive approximation whereas levels and curves are multiplicative
tools, which uses the correct math.) (Similarly, Photoshop's
saturation enhancement is another additive approximation tool
and creates a lot of problems with blocked up colors, and should
only be used sparingly; up to about 12 on the 0 to 100 scale is
OK in my experience and beyond that the additive artifacts show
too much in my opinion.)

I used this CMYK unblocking method on this 4x5 Velvia landscape:
http://www.clarkvision.com/galleries...e_taryall.html
on the red flowers. The web page shows an enlargement
of a red flower.

Roger

 
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acl
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      12-31-2006

Roger N. Clark (change username to rnclark) wrote:
>
> There is a "trick" to recovering detail in blocked up colors
> convert to CMYK space and feather select the blocked-up areas
> then select the channel color opposite what was blocked-up, and change
> the contrast on that channel. For example, if the blocked up
> color is red (e.g. a red flower), convert to CMYK (best if
> your data are 16-bit), select the cyan (C) channel and put a
> selection around the flower. Cyan is blue + green so doesn't
> have red. Change the contrast with the curves tool of the flower
> in that channel. (In Photoshop always use levels or curves to
> change contrast, not the contrast tool. The contrast tool is
> an additive approximation whereas levels and curves are multiplicative
> tools, which uses the correct math.) (Similarly, Photoshop's
> saturation enhancement is another additive approximation tool
> and creates a lot of problems with blocked up colors, and should
> only be used sparingly; up to about 12 on the 0 to 100 scale is
> OK in my experience and beyond that the additive artifacts show
> too much in my opinion.)
>


Thanks, I haven't played much with the CMYK mode. I'll give this a try
on some flower macros I have that have given me trouble printing.

 
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