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From: Robert Spanjaard on 7 Feb 2010 12:31
On Sun, 07 Feb 2010 10:58:09 -0600, Too Funny wrote:

>>Ofcourse, it would be nice to see a response by a PS-user, who can say
>>if the error really is created by PS instead of the original author.
>>I've seen more stupid errors from LL before.
>
> When I spotted the difference on that page I got curious. That's why I
> created that PhotoSlop Granger Chart on the comparison list I posted
> using my own copy of PhotoSlop to see if he made any errors. He did not.
> I even tried changing the system color profiles in PhotoSlop. I changed
> the "rainbow gradient" to the true colors that they should be (they are
> way off in PhotoSlop). They should be, from left to right, in 100%
> saturations:
>
> [...]

Havve you tried other blending modes in PS? Perhaps this is just the way
their Luminance blend is supposed to work.
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).

So apparently a luminosity blend is different from a hard light blend. But
if I convert the PS version to grayscale based on luminosity, I also don't
get a correct black to white gradient.

--
Regards, Robert http://www.arumes.com
From: Paul Furman on 7 Feb 2010 13:25
Robert Spanjaard wrote:
> Too Funny wrote:
>
>>> Ofcourse, it would be nice to see a response by a PS-user, who can say
>>> if the error really is created by PS instead of the original author.
>>> I've seen more stupid errors from LL before.
>>
>> When I spotted the difference on that page I got curious. That's why I
>> created that PhotoSlop Granger Chart on the comparison list I posted
>> using my own copy of PhotoSlop to see if he made any errors. He did not.
>> I even tried changing the system color profiles in PhotoSlop. I changed
>> the "rainbow gradient" to the true colors that they should be (they are
>> way off in PhotoSlop). They should be, from left to right, in 100%
>> saturations:
>>
>> [...]
>
> Havve you tried other blending modes in PS? Perhaps this is just the way
> their Luminance blend is supposed to work.


Screen mode gives a symmetrical chart across the colors, as well as some
other modes, hard light is similar. Immediately after choosing a mode,
hit the up/down arrow keys. Not sure why luminosity works differently in
other programs to the PS luminosity mode but as Alan said, it's still
useful for their purposes or they wouldn't have put it out there,
obviously.

Luminosity means apply the lightness/darkness to the colors, and it's
apparently counting the luminosity of the rainbow layer also, so the
dark blues move down & the light yellows move up. This is the same sort
of issue where you have to be careful what method you use for converting
to b&w.


> 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).
>
> So apparently a luminosity blend is different from a hard light blend. But
> if I convert the PS version to grayscale based on luminosity, I also don't
> get a correct black to white gradient.
>

From: Too Funny on 7 Feb 2010 14:02
On Sun, 07 Feb 2010 10:25:46 -0800, Paul Furman <paul-@-edgehill.net>
wrote:

>Robert Spanjaard wrote:
>> Too Funny wrote:
>>
>>>> Ofcourse, it would be nice to see a response by a PS-user, who can say
>>>> if the error really is created by PS instead of the original author.
>>>> I've seen more stupid errors from LL before.
>>>
>>> When I spotted the difference on that page I got curious. That's why I
>>> created that PhotoSlop Granger Chart on the comparison list I posted
>>> using my own copy of PhotoSlop to see if he made any errors. He did not.
>>> I even tried changing the system color profiles in PhotoSlop. I changed
>>> the "rainbow gradient" to the true colors that they should be (they are
>>> way off in PhotoSlop). They should be, from left to right, in 100%
>>> saturations:
>>>
>>> [...]
>>
>> Havve you tried other blending modes in PS? Perhaps this is just the way
>> their Luminance blend is supposed to work.
>
>
>Screen mode gives a symmetrical chart across the colors, as well as some
>other modes, hard light is similar. Immediately after choosing a mode,
>hit the up/down arrow keys. Not sure why luminosity works differently in
>other programs to the PS luminosity mode but as Alan said, it's still
>useful for their purposes or they wouldn't have put it out there,
>obviously.
>
>Luminosity means apply the lightness/darkness to the colors, and it's
>apparently counting the luminosity of the rainbow layer also, so the
>dark blues move down & the light yellows move up. This is the same sort
>of issue where you have to be careful what method you use for converting
>to b&w.
>

I guess this means anytime someone is using a lighten or darken
(dodge/burn) brush in PhotoSlop or creating any changes in luminosity, like
trying to recover details from shadows or highlights, they can expect all
their colors to get shifted just as badly. Nice! :-)

A good thing my copy was given to me or I wouldn't spend one cent on
something like this. The *ONLY* reason I even keep it on a computer at all
is for the one or two worthwhile plugins that are PhotoSlop dependent. Soon
as I use it for that plugin's effect and am done, it's shut down again with
the hopes that I don't have to ever run it again too soon. There's far too
many better programs out there than having to put up with its nonsense.


From: Paul Furman on 7 Feb 2010 15:13
Too Funny wrote:
> Paul Furmanwrote:
>> Robert Spanjaard wrote:
>>> Too Funny wrote:
>>>
>>>>> Ofcourse, it would be nice to see a response by a PS-user, who can say
>>>>> if the error really is created by PS instead of the original author.
>>>>> I've seen more stupid errors from LL before.
>>>>
>>>> When I spotted the difference on that page I got curious. That's why I
>>>> created that PhotoSlop Granger Chart on the comparison list I posted
>>>> using my own copy of PhotoSlop to see if he made any errors. He did not.
>>>> I even tried changing the system color profiles in PhotoSlop. I changed
>>>> the "rainbow gradient" to the true colors that they should be (they are
>>>> way off in PhotoSlop). They should be, from left to right, in 100%
>>>> saturations:
>>>
>>> Havve you tried other blending modes in PS? Perhaps this is just the way
>>> their Luminance blend is supposed to work.
>>
>> Screen mode gives a symmetrical chart across the colors, as well as some
>> other modes, hard light is similar. Immediately after choosing a mode,
>> hit the up/down arrow keys. Not sure why luminosity works differently in
>> other programs to the PS luminosity mode but as Alan said, it's still
>> useful for their purposes or they wouldn't have put it out there,
>> obviously.
>>
>> Luminosity means apply the lightness/darkness to the colors, and it's
>> apparently counting the luminosity of the rainbow layer also, so the
>> dark blues move down& the light yellows move up. This is the same sort
>> of issue where you have to be careful what method you use for converting
>> to b&w.
>
> I guess this means anytime someone is using a lighten or darken
> (dodge/burn) brush in PhotoSlop

No, the burn & dodge tools work fine on the rainbow layer. It is an odd
behavior though. I sometimes use luminosity mode on adjustment layers,
rather than going to lab mode so that contrast/levels/curves adjustments
don't effect saturation. Hmm, so yeah this does make a difference. If I
try the granger thing in lab mode (set lab before adding layers) that
makes a very different chart with much softer transitions like the gamut
chart they describe in the LL article. Do these other programs have lab
mode? CMYK mode produces yet another different effect.

I checked adjustment layers on a couple normal photos, one with oranges,
one with orages & blues, both have green backgrounds. Lab vs
luminosity-mode adj layers had very slight color shifts making the
yellows brighter, no effect on the blues. Normal mode made the
saturation increase and orange showed more effect. So anyways, yeah, it
does seem to be a bit of a problem but if you don't like the color
shift, add another adjustment layer or use another program if you like.
I've been using photoshop for 20 years so it's what I like working with
and it has a whole lot of tools for whatever needs to be done.

Photoshop is not the tool for scientific experiments & measurement.
Roger Clark found some weird rounding errors & bit depth issues when
using it to make extreme adjustments to shadow detail in raw
conversions. I forget what program he used instead, something designed
for astrophotography manipulations I think. Not the sort of program I'd
like to use for general photo editing.

These days I mostly use Lightroom for tweaking exposures, contrast etc,
which also is not perfect but it's great for workflow. If I'm actually
going to do a large print of a difficult subject, I'll take the raw file
into my old-ish version of photoshop & do fussy stuff like sharpen a
luminosity layer, etc. Otherwise I don't use photoshop unless I need to
do some serious cloning or editing like that. Lightroom is quick and
effective, letting me concentrate on what's important. If a contrast
adjustment increases saturation, I'll just tweak the saturation slider.
If the oranges pop, I'll tune that, etc.


> or creating any changes in luminosity, like
> trying to recover details from shadows or highlights, they can expect all
> their colors to get shifted just as badly. Nice! :-)
>
> A good thing my copy was given to me or I wouldn't spend one cent on
> something like this. The *ONLY* reason I even keep it on a computer at all
> is for the one or two worthwhile plugins that are PhotoSlop dependent. Soon
> as I use it for that plugin's effect and am done, it's shut down again with
> the hopes that I don't have to ever run it again too soon. There's far too
> many better programs out there than having to put up with its nonsense.
>
>

From: Paul Furman on 7 Feb 2010 22:31
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.
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