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Author Topic: 16 Bit Printing  (Read 48096 times)

alain

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Re: 16 Bit Printing
« Reply #120 on: May 19, 2014, 11:52:45 am »

Hi folks,

I'm not sure if the attached VRML file is allowed as file type, but for those who have a VRML viewer plugin (e.g. one from the Cortona3D viewer page) installed in their browser one can display, zoom, and rotate the colorspace hulls in 3D (solid for the smaller gamut and wireframe for the larger gamut colorspace).

It shows that the pRGB colorspace adds a more saturated gamut and specifically darker colors to AdobeRGB, yet covers a reasonably large part of the excessively-large ProPhoto RGB.

Cheers,
Bart

Thanks Bart

Could you compare pRGB to a "good" printer/paper gamut?
or pRGB compared to some camera's  "gamut"?

The more I look at pRGB the better it gets.

Is there a way to find (rather easy) how much % of actual 16-bit prophoto images are out of gamut for pRGB?

Alain
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #121 on: May 19, 2014, 02:13:04 pm »

Could you compare pRGB to a "good" printer/paper gamut?

Hi Alain,

I don't know if this Fine Art paper is a very challenging medium, so let me know if something else is preferred.

Attached:
Hahnemühle Fine Art Baryta glossy (solid hull), inside pRGB (wireframe hull), slight risk of clipping of hyper-saturated orange and mint cyan/green (which the RGB filtered camera probably cannot capture anyway), Perceptual rendering intent can cope with that by modest compression of all colors, while with Relative Colorimetric intent probably only those oranges are at risk. Pro Photo RGB will of course be able to encode almost all of the media gamut, at the cost of posterization risk in (amongst others) sky blues. Both Epson and Canon printer profiles are used. pRGB seems to fit the medium gamut reasonably well.

Do note that it may be required to compress the potential Camera gamut (for very saturated colors) quite a bit (if the image content has such colors) to fit inside the output medium space, but it's good to know where to look for issues, also based on actual image content. Good soft-proofing should identify such issues ahead of time.

Cheers,
Bart
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #122 on: May 19, 2014, 03:05:16 pm »

Could you compare pRGB to a "good" printer/paper gamut?

See earlier post.

Quote
or pRGB compared to some camera's  "gamut"?

This is where things get complicated. In fact, one should look at the intersection between Camera and Output profile gamut and actual image colors in the scene. The Camera RGBs can allow to capture more saturated colors than the output medium's gamut can render, while the output medium's secondary colors (notably orange and cyan green, and some yellows) can have excess room which the camera cannot capture, but may be edited into the image by increasing saturation.

So the question becomes, which colors are in the image itself, can the camera capture those, and how much of that can be printed anyway. Afterall, a red tomato on a red plate won't challenge the cyan greens that the camera cannot capture anyway, but the output medium could print.

Quote
Is there a way to find (rather easy) how much % of actual 16-bit prophoto images are out of gamut for pRGB?

Exactly, that's what is needed, good softproofing. Other than specialist software like Colorthink, I think GamutVision would fit the requirements quite well. Obviously, one would need to purchase it so it would need to satisfy a recurring requirement to be worth the investment.

The Argyll CMS has free tools (which I used to create the VRML files), but that requires one to do some script/batchfile editing to be of use.

Lightroom of course only offers linear gamma ProPhoto RGB to edit in, but it does allow to softproof that with pRGB or an output medium's colorspace.

FWIW, I've attached 3D plots of 2 (solid hull) camera profiles (from CaptureOne) 'inside' pRGB (wireframe hull).

Cheers,
Bart
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David Sutton

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Re: 16 Bit Printing
« Reply #123 on: May 20, 2014, 12:40:13 am »

Thanks to all who are contributing. This is proving a very useful discussion.
I want to be able to "future-proof" my files, and also avoid clipping colours until the output stage, and have always used Prophoto for that reason. I see no reason not to convert my workflow to another colour space, such as BetaRGB if there will be a tangible benefit.
For what it's worth, I've only had a problem with a smooth gradient in one image (blue/greys), and can't say whether it's a problem with the printer hitting its limit, or the colour space.
David
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alain

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Re: 16 Bit Printing
« Reply #124 on: June 10, 2014, 09:01:22 am »

Hi Alain,

A two step profile conversion towards a smaller gamut (and the actually required current output profiles are much smaller) will most likely invoke two rounds of quantizing to smaller integer encoded colorspaces (PPRGB->pRGB->media/display RGB). It's probably safer to just do a single conversion at the end of the process. Whether it makes a visible difference in practice, depends on the actual colors encoded in the image data (with an even smaller required gamut than the output gamut) and print method (e.g. C-print is different from inkjet).

...

Cheers,
Bart
Hi Bart

A  16-bit PPRGB -> 16-bit pRGB -> 8-bit pRGB --> media/display RGB would probably give less errors that a 16-bit PPRGB -> 8-bit PPRGB -->  media/display RGB like in Qimage.

EDIT : And because pRGB is about 40% smaller would give more possible values where the image is in gamut.


Alain
« Last Edit: June 10, 2014, 09:03:16 am by alain »
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #125 on: June 10, 2014, 10:39:18 am »

Hi Bart

A  16-bit PPRGB -> 16-bit pRGB -> 8-bit pRGB --> media/display RGB would probably give less errors that a 16-bit PPRGB -> 8-bit PPRGB -->  media/display RGB like in Qimage.

Hi Alain,

Maybe, maybe not. That's why it's safer to eliminate the PPRGB to begin with. When starting with a smaller gamut colorspace (e.g. pRGB), the subsequent gamut resampling will produce fewer artifacts.

Again, it's rarely the gamut of the actual image data that requires PPRGB. The image data is usually a small subset even of the theoretical maximum that pRGB, or even Adobe RGB (ARGB), could encode. Only with specific colors, saturated and on the axes of the inks colorants, can a wider gamut make some difference.

Quote
EDIT : And because pRGB is about 40% smaller would give more possible values where the image is in gamut.

Indeed, when used as the working space. When used as a space to convert to, as an intermediate, some of the original data may alias a little when several different colors get encoded to the same coordinates (even while remaining in 16-bit/channel).

As a theoretical maximum gamut experiment, see what happens to the RGB16Million.png file, when we run it through several conversions in Photoshop after the initial assignment and mode change to 16-bit:
8-b/ch-->PS16-b/ch-->assigned PPRGB-->pRGB-->ARGB-->8-b/ch = 5762264 colors (=34%) out of 16777216 original colors.
8-b/ch-->PS16-b/ch-->assigned pRGB-->ARGB-->8-b/ch = 7344153 colors (=44%) out of 16777216 original colors.

The lost color differentiation may not be important, if those colors were not in the image data-set to begin with, but it does suggest a higher risk of losing meaningful differences. How much loss, and if it's in smooth gradients, depends on the actual image.

In general, one should reduce the number of recoding operations between colorspaces, and start with a colorspace that is large enough to hold the actual image data and is close to the theoretical maximum gamut of the output profile.

Cheers,
Bart
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alain

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Re: 16 Bit Printing
« Reply #126 on: June 10, 2014, 12:00:22 pm »

Hi Alain,

Maybe, maybe not. That's why it's safer to eliminate the PPRGB to begin with. When starting with a smaller gamut colorspace (e.g. pRGB), the subsequent gamut resampling will produce fewer artifacts.

Again, it's rarely the gamut of the actual image data that requires PPRGB. The image data is usually a small subset even of the theoretical maximum that pRGB, or even Adobe RGB (ARGB), could encode. Only with specific colors, saturated and on the axes of the inks colorants, can a wider gamut make some difference.

Indeed, when used as the working space. When used as a space to convert to, as an intermediate, some of the original data may alias a little when several different colors get encoded to the same coordinates (even while remaining in 16-bit/channel).

As a theoretical maximum gamut experiment, see what happens to the RGB16Million.png file, when we run it through several conversions in Photoshop after the initial assignment and mode change to 16-bit:
8-b/ch-->PS16-b/ch-->assigned PPRGB-->pRGB-->ARGB-->8-b/ch = 5762264 colors (=34%) out of 16777216 original colors.
8-b/ch-->PS16-b/ch-->assigned pRGB-->ARGB-->8-b/ch = 7344153 colors (=44%) out of 16777216 original colors.

The lost color differentiation may not be important, if those colors were not in the image data-set to begin with, but it does suggest a higher risk of losing meaningful differences. How much loss, and if it's in smooth gradients, depends on the actual image.

In general, one should reduce the number of recoding operations between colorspaces, and start with a colorspace that is large enough to hold the actual image data and is close to the theoretical maximum gamut of the output profile.

Cheers,
Bart
Hi Bart

You're example has a "problem" by assigning to PPRGB or pRGB you make those vastly different images.  It's normal that the high values that are assigned PPRGB are outside ARGB.

A better comparison would be :

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->pRGB-->ARGB-->8-b/ch
8-b/ch-->PS16-b/ch-->assigned camera space --> pRGB-->ARGB-->8-b/ch


Alain
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #127 on: June 10, 2014, 12:23:15 pm »

A better comparison would be :

Hi Alain,

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->pRGB-->ARGB-->8-b/ch, gives 4643194 colors.
8-b/ch-->PS16-b/ch-->assigned camera space --> pRGB-->ARGB-->8-b/ch, gives 4643292 colors

A much smaller difference, but again not worse for Printer RGB as working space. I used the EOS 1Ds3 profile, other cameras may show somewhat different results.

Cheers,
Bart
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alain

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Re: 16 Bit Printing
« Reply #128 on: June 10, 2014, 01:43:47 pm »

Hi Alain,

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->pRGB-->ARGB-->8-b/ch, gives 4643194 colors.
8-b/ch-->PS16-b/ch-->assigned camera space --> pRGB-->ARGB-->8-b/ch, gives 4643292 colors

A much smaller difference, but again not worse for Printer RGB as working space. I used the EOS 1Ds3 profile, other cameras may show somewhat different results.

Cheers,
Bart
Hi Bart,

Thanks.  Far better than I expected.  Two that are maybe important for Qimage Ultimate users :

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->8-b/ch-->ARGB
8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB --> pRGB-->8-b/ch-->ARGB


Alain
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #129 on: June 10, 2014, 06:27:09 pm »

Two that are maybe important for Qimage Ultimate users :

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->8-b/ch-->ARGB, results in 3964053 colors.
8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB --> pRGB-->8-b/ch-->ARGB, results in 4160101 colors.
and another
8-b/ch-->PS16-b/ch-->assigned camera space --> pRGB-->8-b/ch-->ARGB, results in 4159482 colors.

Particularly the Conversion of PPRGB to 8-bit seems to take a hit on available colors, as does conversion in 8-b/ch space. Dithering will be required to improve that situation, which is what Qimage now does.

The actual pipeline through Lightroom and Qimage adds dithering at various stages so this is a somewhat simplified situation, besides that it's not really an assignment of the camera space because the camera's Raw data is immediately demosaiced/converted into a working space with some tonemapping and saturation adjustment to something with a potentially larger gamut.

Cheers,
Bart
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alain

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Re: 16 Bit Printing
« Reply #130 on: June 10, 2014, 07:04:29 pm »

8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB-->8-b/ch-->ARGB, results in 3964053 colors.
8-b/ch-->PS16-b/ch-->assigned camera space --> PPRGB --> pRGB-->8-b/ch-->ARGB, results in 4160101 colors.
and another
8-b/ch-->PS16-b/ch-->assigned camera space --> pRGB-->8-b/ch-->ARGB, results in 4159482 colors.

Particularly the Conversion of PPRGB to 8-bit seems to take a hit on available colors, as does conversion in 8-b/ch space. Dithering will be required to improve that situation, which is what Qimage now does.

The actual pipeline through Lightroom and Qimage adds dithering at various stages so this is a somewhat simplified situation, besides that it's not really an assignment of the camera space because the camera's Raw data is immediately demosaiced/converted into a working space with some tonemapping and saturation adjustment to something with a potentially larger gamut.

Cheers,
Bart

Bart

Thanks a lot.

It's simplified, but it's unlikely that an image contains a lot of colors close to the gamut boundary.  It's more a problem with gradients which are inside the gamut of the printer space and are manipulated in 16-b/ch.
The important part of the tests is that going from PPRGB --> pRGB in 16-b/ch is a possible enhancement if it's needed.

 Alain
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #131 on: June 11, 2014, 06:13:01 am »

Bart

Thanks a lot.

It's simplified, but it's unlikely that an image contains a lot of colors close to the gamut boundary.

Correct, and the lost colors are all over the place, not just at the boundaries, so it's hard to predict which colors will be impacted and are also part of the actual image dataset.

Just for the fun of it, I also ran the following tests:
8-b/ch-->PS16-b/ch-->assigned pRGB-->Qimage-->ARGB, results in 5516502 colors.
8-b/ch-->PS16-b/ch-->assigned pRGB-->8-b/ch-->Qimage-->ARGB, results in 7784709 colors.

Qimage does dithering on input of 16-b/ch images as it converts to 8-b/ch, and no dithering on input of 8-b/ch images. No resampling and no sharpening was used, which would have potentially created additional new colors. The final 'output profile' conversion used dithering. On average, the dithering introduced a difference between 16-b/ch and 8-b/ch input with a standard deviation of 0.342 (virtually imperceptible). It looks like 8-b/ch input is not a problem, as is confirmed by actual output.

Cheers,
Bart
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