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PercepTool 2

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  #21  
Old 12-14-2010, 10:22 PM
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Re: PercepTool 2

Focus correction.

HDR might introduce an emphasis on any sensor pattern. Remember the R,G, and B components aren't really at every pixel. The demosaicking process can leave funky artifacts. But that's a stretch to think we can fix it that way.

However, that does argue that HDR should be done with DNG images and the original, uncorrected sensor values. And we demosiack after the fact.

Now MY brain hurts.
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  #22  
Old 12-15-2010, 08:51 AM
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Re: PercepTool 2

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You see, in 8- and 16-bit modes, once you're at max value (255 and 32768, respectively) that's all the channel can hold.
I respectfully suggest you understand what color gamut is vs. the number of bits for encoding said colors (gamut). Again, the bit depth has zero role on the color gamut. You can have an 8-bit (or 16-bit or even 32-bit sRGB document). The same can be true for a ProPhoto Document. The gamut is entirely different.

http://www.adobe.com/digitalimag/pdf..._colspace.pdf:

When you work with 24-bit images, all color and tone is defined in three 8-bit color channels. When you work with wide gamut working spaces, the same bits need to be spread farther apart over the entire color space. Consider this spreading of a finite number of bits as follows: Imagine you have a half-inflated balloon that has 16.7 million dots evenly spaced over its surface. Now you blow up the balloon to twice its original size. Each dot is spread farther apart. When you work with 8-bit-per-channel files, you create this effect when you encode the bits into a progressively larger gamut working spaces. In such situations, it is possible that editing images will produce banding (aliasing). For this reason, should you decide to use a wide gamut working space—for example, something wider than Adobe RGB (1998)—you should attempt to encode the data in 16-bit color. Many capture devices produce more than 8-bits per color and allow you to retain this extra data to use in Photoshop. While the file size will be twice as big and image processing will take longer, you can’t be too careful with your data. You may also wish to use 16-bit data with smaller gamut color spaces.

And the gamut of a capture device is somewhat fixed (in reality, a digital camera has no gamut but rather a color mixing function) yet the facts remain, adding more bits doesn’t extend or enlarge the gamut any more than converting an sRGB document from 8-bits per color to 16-bits per color adds any gamut to the data. It adds more bits but does not extend the color gamut as expressed on some kind of gamut plot (xy chromaticity diagram).

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Precision is why 16-bits is a better space than 8.
Agreed. But that has nothing to do with color gamut.
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  #23  
Old 12-15-2010, 01:11 PM
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Re: PercepTool 2

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Originally Posted by jcr6 View Post
jrp is right -- some windows systems are so locked down that even if we're launched from Photoshop we STILL cannot install. UAC has to be briefly turned off.

I *HATE* Vista and Win7.

In any case, once it is done you can turn UAC back on. I'm sorry it is that way, but it also shows that even though Adobe has supposedly been given permission to write files WITHIN ITS OWN FOLDERS, it still isn't allowed to.

Seriously. Our installer is just a Photoshop script. You'd think that File > Scripts > Browse would just work. But it doesn't.

re: Price. It takes a certain amount of return on investment to get a programmer to write something. I'd NEVER get the value of my time back if I sold it for $6 (like PSKISS). And I'm not the only guy that worked on this.

re: Value for the price. I guess you'll have to try it. The demo is good for a MONTH. No watermarks.
I completely understand your thinking, but the scripts approach does not seem to be a solid long-term solution. Adobe seem to have provided the Adobe Extensions route to enhancing their recent applications. This would avoid having to reboot twice in order to install / update your application, and give greater confidence that your application can be removed cleanly.

Only you can judge whether the expensive route provides a viable business model but, for my part, I cannot justify the cost, particularly when there are competing products available at a fraction of the cost.
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  #24  
Old 12-15-2010, 08:07 PM
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Re: PercepTool 2

Andrew,

Here's an example about gamut that should illustrate my point.

Let's say that I've got a pixel with the following colors: Red = 200, Green = 100, Blue = 50.

If that pixel gets 25% lighter, we're still in gamut: Red = 250, Green = 125, Blue = 62.5 (depending upon the precision, I may or may not be able to represent the actual blue color).

If that pixel gets 30% lighter, we're out-of-gamut in 8- and 16-bit space: Red = 260, Green = 130, Blue = 65. We have no way of representing Red = 260, so Red gets clipped at 255. Now the proportions of Red:Green:Blue are wrong. The color has gone out-of-gamut.

However, in a 32-bit floating point space, there is not a limit at 255. The limit is 10^38, a very large number. Now, in Photoshop the usual number range of 0..255 is covered with 0.0 ... 1.0 (and is a linear space, not a perceptually uniform Gamma 2.2, like in 8- and 16-bit modes). But the ratio of Red:Green:Blue will remain the same for the same color whether the space is linear or not. So if I had a pixel that was Red = 0.8, Green = 0.4, Blue = 0.2 and I made it 30% lighter, I'd get Red = 1.04, Green = 0.52, Blue = 0.26. The Red isn't of gamut because the functional range in PSCS5 is about 2000. We haven't clipped. The color vector is preserved through various processing steps.

So gamut clipping does NOT happen in 32-bit floating point. And for that matter, highlights that are whiter-than-255-white don't get clipped either. That is the primary argument for this space.

Floating point does add more bits, to be sure (23 vs. 15 vs. 8), but it also adds a vast range. It's that added range without clipping that is the point.
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  #25  
Old 12-15-2010, 08:30 PM
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Re: PercepTool 2

Quote:
Let's say that I've got a pixel with the following colors: Red = 200, Green = 100, Blue = 50.
In what color space (which defines the gamut)? You seem to be missing the important point that R0/B0/G255 in ProPhoto is an entirely different color, has a different color gamut, falls within a different area of human perception (plotted on the CIE chromaticity diagram) than sRGB using the identical value!

Quote:
If that pixel gets 30% lighter, we're out-of-gamut in 8- and 16-bit space:
No, it doesn’t. What makes you say that?

You really need to go study the vast differences between what encoding values and color gamut mean and differ. Color Gamut describes the range of colors. It defines where those color plot based on a color space against the only color space we humans need to have defined (human vision). Encoding values do not define gamut, it defines values of colors within a color gamut. More encoding values do not produce more or less gamut. A ProPhoto RGB doc and an sRGB doc in 24 bit color encoding HAVE THE SAME NUMBER of colors. The colors themselves are NOT the same. They fall within different areas of color gamut (based on human vision). There is no number for G255 in sRGB that lies in ProPhoto RGB at G255 because its not in that color space as defined by a set of numeric values.

Numbers alone don’t define a color! Numbers WITH an associated color space do. A color space is simply the plot of colors we can see based on experiments done before you and I were born when there was no such thing as computer encoding.

Ask ANY color scientist you can find, or any decent software engineer that writes code for dealing with color imaging if the encoding values affect color gamut. Cause the two are totally separate. The gamut of a ProPhoto RGB document is no different if its in 24 bit or 48 bit color.

You are missing a fundamental understanding of color gamut and encoding values used to define those colors. More bits, more color values, no more (or less) color gamut. Again, color gamut defines a range of colors. Bit depth defines the number of colors. More colors doesn’t equal more gamut.

Here’s a simple plot of two well know color spaces against the color gamut of human vision. They are differing sizes in gamut solely based on where their RGB primaries fall on this larger plot. It doesn’t matter what the encoding is (how many bits), the RGB values (the numbers you quote without the important info, the color space which defines what those colors look like to us humans), have no bearing on their positions on this plot. I don’t know how to make this any more simple for you.

http://digitaldog.net/files/sRGBvsProPhoto2d.jpg

Last edited by andrewrodney; 12-15-2010 at 08:51 PM.
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  #26  
Old 12-15-2010, 08:46 PM
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Re: PercepTool 2

Even nvidia provides a 101 on encoding and gamut here:

http://www.nvidia.com/docs/IO/40049/...01_v02_new.pdf

Quote:
Concepts of bit depth and color gamut while related should be looked as two separate items. Bit depth, the 30-bit part of “30-bit color” is a reference to how many bits of data are allocated for each color value in a pixel. Color Gamut refers to how much color a display or printer can give. It is possible to have a format with a high bit depth even though it is a low color gamut.
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  #27  
Old 12-15-2010, 09:52 PM
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Re: PercepTool 2

Will you at least stipulate that at some point a color channel can get a value larger that 255?

SHEESH!
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  #28  
Old 12-15-2010, 09:55 PM
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Re: PercepTool 2

And you're still talking about bits and I'm not.

Specifically a 32-bit number is FLOATING POINT.

The range that Adobe is using for normal images is 0.0 to 1.0.

I'm not talking about bits and precision (except that there is a lot). I'm saying that we can represent values larger than 255/1.0 in any/every channel and not lose those values.

Instead you're still trying to beat me up on the definition of "gamut".

No matter what the color space might be, if your channel value exceeds 255 (in 8- or 16-) it's TOAST.
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  #29  
Old 12-16-2010, 08:46 AM
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Re: PercepTool 2

I didn’t beat you up, I’m correcting a statement you made that is factually incorrect:
Quote:
Why 32-bit mode? A: Because out-of-gamut colors don't clip.
The bit depth has nothing to do with color gamut or gamut clipping period. Use the term color gamut correctly or don’t use it at all, that’s about the only beating I’d give you.

As the Chinese proverb says: The first step towards genius is calling things by their proper name.
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  #30  
Old 12-16-2010, 08:56 AM
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Re: PercepTool 2

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No matter what the color space might be, if your channel value exceeds 255 (in 8- or 16-) it's TOAST.
Numbers without an associated color space are totally ambiguous! That is the next idea you need to look at. R255/G0/B0 is not a color (color is a perceptual phenomena, not a numeric one). R255/G0/B0 in sRGB is a color based on human perception and we can easily plot and define that color. R255/G0/B0 in Adobe RGB is a different color (the numbers are the same, get it?). Typing out numbers without a color space is as ambiguous as me telling you I weigh 175. 175 pounds? Kilo’s? You can’t just spit out numbers for colors without a scale (that’s what a color space defines). Since you brought up gamut, color cannot be kept out of this discussion (otherwise stop talking about gamut clipping and color gamut).

Quote:
I'm one of the authors of PercepTool. As you've observed above there are indeed three parts, and I'd like to outline them, what they're for, why they are separate, and the advantages of 16- and 32-bit modes respectively.
Your points about this product would be far better received if you stuck to commonly agreed and understood terminology with respect to color, encoding etc. I have no idea about HDR past the one book I’ve read, I have no dog in that fight. But if you come to a forum and talk about color gamut and encoding while representing your product, and do so by making statements like Why 32-bit mode? A: Because out-of-gamut colors don't clip, at least make your points technically correct. The term gamut and gamut clipping are well established terms in color management, something I know a bit about.
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