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From: Pete on 7 Feb 2010 22:57
Paul Furman wrote:
> On 2/7/2010 5:36 PM, Pete wrote:
> > ...
>> Now, given our horizontal colour gradient with S=100% and H going from
>> 359�
>> down to 0� left to right, what will happen when we attempt to change the
>> luminance from 0 at the bottom to 100% at the top?
>> ...
>> Red around one third of the way up.
>> Green around two thirds of the way up.
>> Blue around a tenth of the way up.
> > ...
>
> Over my head
> ...but that got me thinking about lab color space and there's some
> interesting similar issues involved there:
> http://en.wikipedia.org/wiki/Lab_color_space
>
> In any case, I reproduced the chart like the others using two blending
> modes, patched together:
> http://www.flickr.com/photos/edgehill/4339700662/
> see the other similarly named thread for that discussion.
>
> Each of the blending modes does a different calculation like your
> formulas. You can see a few different approaches in adjacent pics at that
> link, including lab mode.

Thanks Paul.

I've been looking carefully at the Granger charts shown in this thread. For
the printer I use the PS chart shows the effect of limited gamut more
obviously than the others - meaning it takes less time to see the effect.

Certainly, the other editors are not performing a luminance blend, they must
be doing brightness, lightness, or intensity instead.

Anyone know where the original Granger chart can be found? I've nearly worn
out Google trying to find it (or just Granger's description of it).

Pete


From: Paul Furman on 7 Feb 2010 23:01
On 2/7/2010 12:13 PM, Paul Furman wrote:
> Photoshop is not the tool for scientific experiments & measurement.

I take that back, mostly. There are probably some fine rounding error
and bit depth nitpicks but this issue turned out to be just a different
way of calculating:
http://www.flickr.com/photos/edgehill/sets/72157623375625518/detail/
From: Arthur Entlich on 8 Feb 2010 05:08
I am going to jump into this discussion with an idea, not based upon any
direct knowledge I have as to why Photoshop is designed as it is, but
with a mind toward human vision.

Human vision is not linear at all. We see by two structures, rods, which
perceive luminosity without color, and cones, three forms of which each
see a different light frequency range, the "red" cones actually peak at
yellow, green cones peak at green and blue cones peak in the violet part
of the spectrum. These structures are not evenly distributed in terms
of numbers or locations. Rods are more concentrated at the edges of our
retina and are used in our peripheral vision, which has poor color
vision. Cones are more concentrated in the middle of the retina.

While the percentages of the three cone cells vary considerably between
adults, thus creating the various levels and forms of color blindness,
overall adults have very poor blue-violet color perception. We are born
with less blue cones than either the red or green. Early in life,some
are destroyed by UV light entering the eye. The UV also damages the
transparent and neutral lens of the eye, slowly yellowing it until it is
almost orange juice color as we pass middle age. While this yellowing
actually filters the UV light reaching the retina, and therefore
protects the blue cones left, it also filters out a huge amount of the
blue light that reaches the retina, so a mixture of low blue cones to
begin with, damage by UV early in life, and then a fairly heavy yellow
orange filtration, means our blue perception stinks.

While we are very attentive to reds, due to the evolutionary
significance of red to yellow, it is the second smallest number of
cones. So, while we are more aware of reds, we actually have less red
cones to see it with. Our largest number of cones are greens, in most
people by a substantial amount. This allows us to see green
differentials quite well, and is probably significant because vegetation
coloration can be important to survival.

Now, I'm not sure what Photoshop is up to with their Granger Calibration
Chart differences (yet at least - I've asked a friend who is a color
engineer if he had any comments) but as someone who has a background
with the human side of color perception, it may be that Adobe has made
some accommodation for the species who use their programs, with our
non-linear color perception.

Art




If you are interested in issues surrounding e-waste,
I invite you to enter the discussion at my blog:

http://e-trashtalk.spaces.live.com/

Paul Furman wrote:
> On 2/7/2010 12:13 PM, Paul Furman wrote:
>> Photoshop is not the tool for scientific experiments & measurement.
>
> I take that back, mostly. There are probably some fine rounding error
> and bit depth nitpicks but this issue turned out to be just a different
> way of calculating:
> http://www.flickr.com/photos/edgehill/sets/72157623375625518/detail/
From: Paul Furman on 8 Feb 2010 09:39
Robert Spanjaard wrote:
> If I convert my own chart to grayscale based on luminosity, I don't get an
> even black to white gradient (which I do get with a Lightness grayscale).

Oh, I see what you mean. The odd looking asymmetrical PS version, if
converted to grayscale, goes to a perfect gradient black on bottom,
white on top. The others show dark & light vertical shapes like the
color version. BTW I did a version in lab mode and had to convert to RGB
for web... that rgb version looks very similar but doesn't go back to a
smooth gradient but if I flatten the psd and convert that to grayscale
while still in lab, it works. The lab version takes out the weird
angular components, apparently lab is designed to transition more
smoothly & match human vision better.

None of these gives the appearance of a 'true' parallel set of vertical
rainbow bands fading from black to white which one might expect from the
exercise. Optics can be similarly baffling where you correct for
spherical aberration, certain kinds of chromatic aberrations get worse
or the bokeh goes ugly, etc.
From: ray on 9 Feb 2010 15:16
On Sun, 07 Feb 2010 09:52:22 -0600, Too Funny wrote:

> I thought it would be fun to add yet one more graphic editor into the
> testing results, and then combine them all into one easy to see chart so
> people don't have to bother clicking on 5 different links. Then trying
> to remember what you saw at each one (I know how slow some of you are).
>
>
> "Granger Calibration Chart" Editor-Test Results
>
> http://farm3.static.flickr.com/2775/4337905568_55c1e9cfa6_o.jpg
>
> Isn't this fun? :-)

I'd have thought there'd be a lot more to photo editing.
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