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Crisp look? Sharpening in LAB?

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  #31  
Old 04-10-2012, 03:12 PM
kav kav is offline
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Re: Crisp look? Sharpening in LAB?

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Originally Posted by andrewrodney View Post
Cause there is no such thing as a wide gamut CMYK space, CMYK is an output device dependant color space, moving from RGB to CMYK and back (or CMYK to CMYK) is not a very good idea!
Hey.... for once we agree .
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  #32  
Old 04-11-2012, 12:59 AM
capice capice is offline
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Re: Crisp look? Sharpening in LAB?

...at last
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  #33  
Old 04-16-2012, 09:39 PM
franko60 franko60 is offline
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Re: Crisp look? Sharpening in LAB?

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Cause there is no such thing as a wide gamut CMYK space, CMYK is an output device dependant color space, moving from RGB to CMYK and back (or CMYK to CMYK) is not a very good idea!
Au contraire, mon ami. If you visit the web site I gave you will find you can indeed download a wide gamut CMYK profile. This allows you to convert from any of the RgB spaces to CMYK which in turn allows you to do certain adjustments, such as sharpening on the K layer, which you cannot do in the RgB space. Dan Margulis did a series on this in Photoshop User back in the days when it only came in a dead tree format. I'll see if I can dig it out and find the month and year.
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  #34  
Old 04-16-2012, 11:55 PM
capice capice is offline
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Re: Crisp look? Sharpening in LAB?

As far as I know Dan Margulis's method converts to LAB or am I mistaken?
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  #35  
Old 04-17-2012, 01:53 AM
franko60 franko60 is offline
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Re: Crisp look? Sharpening in LAB?

Dan does a lot of work in the Lab space; however, this particular tutorial used a wide gamut CMYK space. The ICM profile is available from www.curvemeister.com.

...and it works. Because there is not much detail in the K channel where people are concerned you can sharpen to a much greater extent on the black channel than you can on any colour channel. And because the profile is wide gamut (note - it is not a printing profile!) you do not lose any colour information converting from and back to RGB.

But don't take my word for it. Go to curvemeister.com, download the wide gamut CMYK profile and see just how much you can sharpen on the black channel before the image starts looking over sharpened. Then convert back to RGB and see how little colour artefacts are produced. Just make sure you're using the wide gamut profile. It is called WGCMYK, GCR, Light b85 11-14-01.icm

Last edited by franko60; 04-17-2012 at 02:01 AM.
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  #36  
Old 04-17-2012, 08:34 AM
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andrewrodney andrewrodney is offline
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Re: Crisp look? Sharpening in LAB?

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Originally Posted by franko60 View Post
Au contraire, mon ami. If you visit the web site I gave you will find you can indeed download a wide gamut CMYK profile.
You plot this gamut in 3D as I did? If so, you should re-examine the idea it is wide gamut. It’s a tad smaller in overall gamut than Adobe RGB (1998)* which is pretty wide for a CMYK space but inadequate in gamut size for all kinds of work. So even if you are working with Adobe RGB (1998) and worse, ProPhoto used in Adobe raw converters, you’re clipping colors converting to this space for any questionable reason other than you are in love with output specific CMYK color models. Silly.

*Gamut volume 1188820 vs, 1207529.
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  #37  
Old 04-17-2012, 08:36 AM
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andrewrodney andrewrodney is offline
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Re: Crisp look? Sharpening in LAB?

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Originally Posted by franko60 View Post
Then convert back to RGB and see how little colour artefacts are produced.
I don’t want any color artifacts. I don’t want to spend time converting color spaces to conduct an edit I don’t have to. This idea being sold on the site is a solution in search of a problem.
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  #38  
Old 04-17-2012, 08:49 AM
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andrewrodney andrewrodney is offline
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Re: Crisp look? Sharpening in LAB?

Interestingly enough, I took an 8-bit Lab Granger rainbow and converted to this so called wide gamut CMYK profile and back. Nothing more. Using a product called ColorThink, I can plot all the unique colors contained in the two images. Net result was just converting to CMYK and back hosed 2853 unique colors out of an original of 16305.
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  #39  
Old 04-17-2012, 09:56 AM
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Mike Needham Mike Needham is offline
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Re: Crisp look? Sharpening in LAB?

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So even if you are working with Adobe RGB (1998) and worse, ProPhoto used in Adobe raw converters
Without any wish to hijack a thread, I found this interesting. As someone who converts to ProPhoto from raw, I am interested in the cardinal sin I am committing (genuinely). I was of the opinion that ProPhoto was a wide gamut space (or is the obvious still not as wide as LAB argument still the king?). I use it because I thought it was an accepted standard and because it contains virtually all perceptible real world colours. I of course recognise a bit of class when I see it, so would appreciate your input.

Would appreciate any feedback.
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  #40  
Old 04-17-2012, 11:08 AM
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Re: Crisp look? Sharpening in LAB?

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Originally Posted by Mike Needham View Post
Without any wish to hijack a thread, I found this interesting. As someone who converts to ProPhoto from raw, I am interested in the cardinal sin I am committing (genuinely). I was of the opinion that ProPhoto was a wide gamut space (or is the obvious still not as wide as LAB argument still the king?).
Raw data has no defined color space. It is essentially Grayscale data. And it isn’t anything like the RGB working spaces we deal with.

In any raw converter, that converter has to make an assumption of the raw color space (unless they have the spectral sensitivities of the chip, something probably only the manufacture has). At some point, the assumption of the sensor colorimetry is used along with a processing color space. In Adobe raw converters, that color space is ProPhoto primaries with a linear encoding (gamma if you will).

My point is, with Adobe raw converters, you’re using ProPhoto RGB. The reason it is used is due to it’s very large size and the very large potential gamut of this data! While I don’t know for a fact, my suspicion is that Aperture uses Adobe RGB instead of ProPhoto RGB when it handles raw data. So at least in terms of Adobe raw converters, using anything smaller than ProPhoto from the raw converter potentially clips colors. I say potentially because if you capture an image on your DSLR of a gray card, or say a bride in a white wedding dress, it is quite possible the scene gamut is far smaller than ProPhoto RGB.

There are no prefect RGB working spaces or we’d only have one. In terms of a wide gamut space, ProPhoto is even larger overall than Lab. But some of that is wasted in that two of the primaries fall outside the spectrum locast (Lab is basically the size here; it is a variant of CIE XYZ that defines human color vision). All RGB working spaces have to use three primaries that create a very simple shape (viewed 2D it appears like a triangle). ProPhoto has two primaries outside human vision because in order to produce a very large gamut RGB space, the three triangular shapes have to expand outward.

There are no input or output spaces that use Lab. That is, all capture color spaces are RGB. An output color space can be RGB, CMYK, CCMMYKK etc. But never Lab.

Lab was NEVER designed for use as an editing space. Keep in mind that the Lab color model was invented way back in 1976, long before anyone had thoughts about digital color management or Photoshop. Keep in mind that Lab was just an attempt to create a perceptually uniform color space where equal steps correlated to equal color closeness based on the perception of a viewer. The CIE didn't claim it was prefect (cause its not). Most color scientists will point out that Lab exaggerates the distance in yellows and consequently underestimate the distances in blues. Lab assumes that hue and chroma can be treated separately. There's an issue where hue lines bend with increase in saturation perceived by viewers as an increase in both saturation and a change in hue when that's really not supposed to be happening. Further, according to Karl Lang, there is a bug in the definition of the Lab color space. If you are dealing with a very saturated blue that's outside the gamut of say a printer, when one uses a perceptual rendering intent, the CMM preserves the hue angle and reduces the saturation in an attempt to make a less saturated blue within this gamut. The result is mathematically the same hue as the original, but the results end up appearing purple to the viewer. This is unfortunately accentuated with blues, causing a shift towards magenta.

So in terms of a raw workflow, getting ProPhoto out of the converter and sticking with it makes the most sense if you feel that color space conversions should be kept to a minimum for reduced data loss and time loss. At some point we are going to have at least one more conversion anyway (to output the data). The idea that you’d convert RGB data to a smaller CMYK space just to sharpen it seems counter productive in so many way. The CMYK sharpen the black channel advocates need to prove with actual image files and better still good output that this technique is superior to proper sharpening techniques either in a raw converter or afterwards in Photoshop on the original RGB data. Otherwise they are wasting bits and time.
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