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Alan Browne wrote:
> Can anyone shed light on this?
>
> 1) In PS, follow the instructions at:
>
> http://www.luminous-landscape.com/es...t-charts.shtml and generate
> the Granger chart as shown. Oddly, it has a strange distribution given
> that the gradient layer is linear top-to-bottom. What is creating those
> diagonals in the chart?
>
> 2) For comparison, see;
>
> http://farm3.static.flickr.com/2790/...f5e104ff_o.jpg
>
>
Perhaps simply because the individual gradients themselves are
non-linear, compared to gradients applied by other photo-editing programs.
Gimp "colorcube analysis" shows the non-linearity of the gradients here:
http://i49.tinypic.com/25jxge9.png
Gradients produced in Gimp (the same as gradients produced in other
programs) are on the left).

Mike Russell wrote:
> On Mon, 08 Feb 2010 09:34:07 +1300, Me wrote:
>
>> Alan Browne wrote:
>>> Can anyone shed light on this?
>>>
>>> 1) In PS, follow the instructions at:
>>>
>>> http://www.luminous-landscape.com/es...t-charts.shtml and generate
>>> the Granger chart as shown. Oddly, it has a strange distribution given
>>> that the gradient layer is linear top-to-bottom. What is creating those
>>> diagonals in the chart?
>>>
>>> 2) For comparison, see;
>>>
>>> http://farm3.static.flickr.com/2790/...f5e104ff_o.jpg
>>>
>>>
>> Perhaps simply because the individual gradients themselves are
>> non-linear, compared to gradients applied by other photo-editing programs.
>> Gimp "colorcube analysis" shows the non-linearity of the gradients here:
>> http://i49.tinypic.com/25jxge9.png
>> Gradients produced in Gimp (the same as gradients produced in other
>> programs) are on the left).
>
> Photoshop can provide linear gradients, but not by default. Use
> Photoshop's gradient editor, set the smoothing parameter to zero, and no
> dither. Why did they do it this way? Why ask why.
>
Thanks - that works - problem solved.
Now perhaps someone can advise Ludicrous Landscape's editors with
instructions on how to make a "proper" Granger chart.

On 2/9/2010 8:52 PM, Mike Russell wrote:
> On Tue, 09 Feb 2010 16:14:44 -0500, Alan Browne wrote:
>
>> On 10-02-07 19:40 , Mike Russell wrote:
>>
>>>
>>> Photoshop can provide linear gradients, but not by default. Use
>>> Photoshop's gradient editor, set the smoothing parameter to zero, and no
>>> dither. Why did they do it this way? Why ask why.
>>
>> Hi Mike, I followed your instructions, but I do not get the 'standard'
>> Granger. I set no dither for both the spectrum and the gradient. I set
>> smoothing to 0 (for either and both). But I do not get the Granger w/o
>> the artifacts. Any idea what I'm missing?
>>
>> (If I do this with "HardLight" instead of Luminosity, it does work).
>
> Photoshop is giving an accurate result in both cases. The hard light layer
> will darken RGB values of the target layer for values less than 128, and
> lighten it for values greater than 128. The result is an artifact free
> Granger chart, similar to what you see from other products.

Hard light is not exactly the same, I managed to make a matching chart
with Screen mode above 128 and Multiply mode below 128. That's what most
programs call luminosity. The question is why the different approaches?


> Luminosity is a hue dependent function, weighted by the luminosity values,
> with b the darkest and green the lightest of the rgb primaries. It's not
> possible, in RGB space, for a pure blue to have a luminosity greater than
> 11%. Above that it is necessary to add white to the blue to get the value
> dictated by the luminosity layer.
>
> The zig zag artifact has six peaks, one for each primary of the HSL
> hexcone. Another way to think of it is a plot of the luminosity of various
> mixtures of r, g, and b, with blue being the darkest, and yellow being the
> lightest. Or think of it as a flattened cylindrical projection of the HSL
> hexcone.
>
> Jacob Rus has recently done a wiki page on HSL and HSB. The "set height
> from luma" operation shown in the geometric derivation illustration is what
> is happening with Photoshop's luminosity mode.

http://en.wikipedia.org/wiki/HSL_and_HSV
That first illustration looks a lot like what we are discussing here.


Math for luma figured into the best explanation I could find. That
explained the asymetrical humps in the PS version with 'luminance' but
what is the scheme that shows symmetrical peaks in the diagram and why
did the other programs chose that math for what they call luminance? The
big difference I saw was that if you convert to grayscale, the PS
version goes to a smooth transition where the other shows the colors for
their lightness: yellow is light, blue is dark, green and red
intermediate. The PS version preserves grayscale lightness/darkness as
can be seen in the last frame of the set below.

Here's examples and the blending modes used to achieve them:
http://www.flickr.com/photos/edgehil...7623375625518/
I also tried it in lab mode, out of curiosity.
#2 was pasted together from using those two blending modes for top &
bottom, then squishing them back to fit in a square. Most programs work
this way for what they call luminance. #1 is the default PS behavior.

At first I was just curious but I do use the luminance blending mode
pretty often on contrast type adjustment layers so that I can tweak
curves or levels without changing saturation. Normally a contrast
increase will give a more saturated image and I often like to keep
things subtle. I'm aware that lab mode is the better way to do this but
it's a hassle and I'm just not in the habit of working in lab. Is the
luminosity blend mode going to mess up my colors? Like if curves darken
a blue area, it looks like that might turn pale. Or maybe this really is
the better way to do it and actually preserves luminosity better.

On 2/11/2010 10:00 PM, Mike Russell wrote:
> On Thu, 11 Feb 2010 11:02:52 -0800, Paul Furman wrote:
>
>> On 2/9/2010 8:52 PM, Mike Russell wrote:
>>> On Tue, 09 Feb 2010 16:14:44 -0500, Alan Browne wrote:
>>>
>>>> On 10-02-07 19:40 , Mike Russell wrote:
>>>>
>>>>>
>>>>> Photoshop can provide linear gradients, but not by default. Use
>>>>> Photoshop's gradient editor, set the smoothing parameter to zero, and no
>>>>> dither. Why did they do it this way? Why ask why.
>>>>
>>>> Hi Mike, I followed your instructions, but I do not get the 'standard'
>>>> Granger. I set no dither for both the spectrum and the gradient. I set
>>>> smoothing to 0 (for either and both). But I do not get the Granger w/o
>>>> the artifacts. Any idea what I'm missing?
>>>>
>>>> (If I do this with "HardLight" instead of Luminosity, it does work).
>>>
>>> Photoshop is giving an accurate result in both cases. The hard light layer
>>> will darken RGB values of the target layer for values less than 128, and
>>> lighten it for values greater than 128. The result is an artifact free
>>> Granger chart, similar to what you see from other products.
>>
>> Hard light is not exactly the same, I managed to make a matching chart
>> with Screen mode above 128 and Multiply mode below 128. That's what most
>> programs call luminosity. The question is why the different approaches?
>>
>>
>>> Luminosity is a hue dependent function, weighted by the luminosity values,
>>> with b the darkest and green the lightest of the rgb primaries. It's not
>>> possible, in RGB space, for a pure blue to have a luminosity greater than
>>> 11%. Above that it is necessary to add white to the blue to get the value
>>> dictated by the luminosity layer.
>>>
>>> The zig zag artifact has six peaks, one for each primary of the HSL
>>> hexcone. Another way to think of it is a plot of the luminosity of various
>>> mixtures of r, g, and b, with blue being the darkest, and yellow being the
>>> lightest. Or think of it as a flattened cylindrical projection of the HSL
>>> hexcone.
>>>
>>> Jacob Rus has recently done a wiki page on HSL and HSB. The "set height
>>> from luma" operation shown in the geometric derivation illustration is what
>>> is happening with Photoshop's luminosity mode.
>>
>> http://en.wikipedia.org/wiki/HSL_and_HSV
>> That first illustration looks a lot like what we are discussing here.
>>
>>
>> Math for luma figured into the best explanation I could find. That
>> explained the asymetrical humps in the PS version with 'luminance' but
>> what is the scheme that shows symmetrical peaks in the diagram and why
>> did the other programs chose that math for what they call luminance?
>
> I think the other programs simply multiplied the RGB channels equally by
> the grayscale value over 255.
>
>> The
>> big difference I saw was that if you convert to grayscale, the PS
>> version goes to a smooth transition where the other shows the colors for
>> their lightness: yellow is light, blue is dark, green and red
>> intermediate. The PS version preserves grayscale lightness/darkness as
>> can be seen in the last frame of the set below.
>>
>> Here's examples and the blending modes used to achieve them:
>> http://www.flickr.com/photos/edgehil...7623375625518/
>> I also tried it in lab mode, out of curiosity.
>> #2 was pasted together from using those two blending modes for top&
>> bottom, then squishing them back to fit in a square. Most programs work
>> this way for what they call luminance. #1 is the default PS behavior.
>>
>> At first I was just curious but I do use the luminance blending mode
>> pretty often on contrast type adjustment layers so that I can tweak
>> curves or levels without changing saturation. Normally a contrast
>> increase will give a more saturated image and I often like to keep
>> things subtle. I'm aware that lab mode is the better way to do this but
>> it's a hassle and I'm just not in the habit of working in lab. Is the
>> luminosity blend mode going to mess up my colors? Like if curves darken
>> a blue area, it looks like that might turn pale. Or maybe this really is
>> the better way to do it and actually preserves luminosity better.
>
> It all depends on the image - the important thing is to be quick enough in
> your workflow to try it one way, then another, and compare results. Dan
> Margulis's Picture Postcard workflow is an example of this, though it is
> done with a combination of curves and Photoshop's apply image command.
>
> Speaking of just blues in the context of sky - most viewers like skies to
> be dark and saturated, so yes, applying a luminosity layer to a blue sky
> would generally lighten it. In this case you would use apply image, uaing
> the red channel in luminosity mode, and use a curve to boost the effect
> further. If there are important foreground elements, then use the green or
> blue channels (or the b channel in Lab) as a mask.
>
> There are dozens of ways to use curves, masking, apply image, layer
> blending, and other functions, each of which adds a bit of punch to your
> image as far as color or detail.
>
> BTW - on your flickr page you pose the question of why use a Granger chart
> at all - for me it's a curiousity item that is helpful for understanding
> the RGB color space, but nothing more than that. As an artificial
> gradient, it is of no relevance to photography or printing related to
> photography.

Thanks! I've been discovering snapshots on the history toolbar are good
for that filp-back-n-forth type comparison; an effective way to evaluate
complex options.

I take it you mean, if blues are getting washed out, then just work on
the red (and or green) channel of an adjustment layer (when setting
luminance blend mode to avoid saturation changes as I described). I
tried that on one typical sort of landscape with a washed out sky and
all it did was emphasize the dark vignetting in the corners, so yeah, it
all depends on the image and any number of tweaks can be applied till it
looks right.

The value of the chart for general comprehension is like this question -
looking at a few of these charts flipping through the blend modes has
helped me understand blend modes and what to look for.

Mike Russell wrote:
> On Wed, 10 Feb 2010 18:15:55 -0500, Alan Browne wrote:
>
>> On 10-02-10 17:25 , Mike Russell wrote:
>>> On Tue, 09 Feb 2010 23:56:35 -0500, Alan Browne wrote:
>>>
>>>> I really wanted to know why if I'm following your instructions, I'm not
>>>> getting your result. Someone else did. ("Me" but not me).
>>>>
>>>> eg: I'm doing something wrong in the process.
>>> I think they were referring to the gradient not having a clean histogram,
>>> rather than the result with the granger chart. The granger chart will
>>> have the artifacts you mention for Luminosity, because of the relationship
>>> of hue and luminosity, but not for other modes such as hard light.
>>
>> You're not hearing me.
>>
>> "Me" (a different poster) followed your suggestion for turning off
>> dithering and setting smoothing to 0. Using Luminosity He got a
>> nominally correct Granger.
>>
>> I (that is me, not "Me") followed your instructions and did not get the
>> nominally correct Granger using Luminosity (I did with "Hardlight").
>>
>> What could account for the different result?
>
> I think I'm hearing both you, and Me. I guess we'll just have to wait for
> Me to clear up the matter.
You solved the problem with non-linear gradients.
The relationship between luminosity and hue in photoshop also explains
why the method suggested by Luminous Landscape fails.
It remains a mystery why Luminous Landscape didn't see that their
"Granger chart" was a shameful mistake, and a further mystery - to me
anyway - why they thought that a Granger chart was useful, except as a
curiosity. They also failed to suggest that using jpeg compression on
such a chart was a waste of time and to be seriously avoided, and why on
the sort of monitors many people use these days, correct display of
gradients can be a big problem.
But from years of reading articles about photography on Luminous
Landscape, I'd come to the conclusion that they are a pretty hapless lot
of obsessive gadget-geeks, not real photographers.