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Old 30-11-2015, 11:14 AM
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Shiraz (Ray)
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display technology - need help

Hi
a recent image elicited a couple of responses that low spatial frequency blue noise could be seen in the background. On my monitor it does not show to any noticeable degree. I trust the judgement of those who posted, so the question is, why the difference?

1. my monitor is an IPS with 6 bit hardware and dithering to 8 bits. It is claimed to display 72% NTSC, which presumably means full sRGB and it calibrates well against on-line test patterns.
2. my understanding is that my graphics card has 24bit display memory
3. my images to date are all RGB gamut.
4. my understanding is that most popular software and the internet is sRGB by default

questions:

1. could the display of limited RGB gamut images on a broad gamut monitor result in enhanced visibility of noise (one source suggested that such a mismatch could produce odd effects)? or
2. Is my monitor insufficient to show underlying noise and do I need something better (it looks pretty good on test patterns)?
3. would screen calibration hardware help much on a 6 bit dithered screen driven by 8 bit graphics technology?

be very grateful for any help. Thanks, Ray

Last edited by Shiraz; 30-11-2015 at 12:58 PM.
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Old 30-11-2015, 11:40 AM
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Hi Ray,

I have a fairly decent calibrated screen at home (NEC PA271W.) I'll have a look at the image tonight and let you know if I can see the background noise.

Cheers,
Rick.
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Old 30-11-2015, 11:53 AM
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Hi Ray,

I have a fairly decent calibrated screen at home (NEC PA271W.) I'll have a look at the image tonight and let you know if I can see the background noise.

Cheers,
Rick.
Thanks very much Rick.

I don't doubt that others can see some noise, but wondered specifically if this might be due to displaying an sRGB image using a monitor set to display in NTSC or Adobe gamuts. Clutching at straws maybe and will get a new monitor if need be.
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Old 30-11-2015, 04:01 PM
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I find there is a major difference between various monitors. My laptop for example shows it with a blue bias and is weak in reds. The same image on another monitor is much more red/yellow.

I got a Samsung tablet as a double check as I find smart phone screens and tablets seem pretty colour accurate.

Greg.
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Old 30-11-2015, 05:35 PM
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Quote:
Originally Posted by gregbradley View Post
I find there is a major difference between various monitors. My laptop for example shows it with a blue bias and is weak in reds. The same image on another monitor is much more red/yellow.

I got a Samsung tablet as a double check as I find smart phone screens and tablets seem pretty colour accurate.

Greg.
thanks Greg. yep there sure is variability in displays - that was why I got a reasonably good quality monitor to do the final processing before posting.

If there is a significant problem with my monitor, my processing techniques or my imaging gear, I want to know. The main issue for now is that I really understand only a tiny bit when it comes to colour gamuts, monitor technology etc.
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Old 30-11-2015, 06:56 PM
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Ray,

If I display your original image on my wide gamut (only a smidge away from full AdobeRGB) display with colour management disabled then the background is ugly with a blotchy coloured background. The blues in the galaxy also look a lot more cyan. With colour management enabled it looks fine.

With colour management disabled, the version with the desaturated background looks much better but the galaxy colour is still too cyan. The spatial filterered version looks as bad as the original.

If I view one of my own sRGB images with colour management disabled the blues also look too cyan and the background is OK apart from being a little bright. I believe this is because I go to some effort to desaturate my backgrounds.

It would be interesting to see how the image looks on your screen without colour management. If you have Photoshop you can set your working space to something other than sRGB and tick the Profile Mismatches/Ask When Opening option in the Color Settings dialog, then use the Discard the embedded profile option when you open the image.

You seem to be doing everything by the book and I can't see how you could improve your workflow apart from stomping more heavily on the background.

Cheers,
Rick.
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Old 30-11-2015, 09:02 PM
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thanks very much Rick. That is somewhat comforting in that it looks like a processing issue and there may be a couple of ways to fix the problem. Really appreciate the advice.

thanks also to Greg for pointing out a problem that I didn't know I had.

will post again when I have done a bit more investigation - maybe I can even learn enough to say something useful .

regards Ray
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Old 01-12-2015, 03:42 AM
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Quote:
Originally Posted by Shiraz View Post
thanks Greg. yep there sure is variability in displays - that was why I got a reasonably good quality monitor to do the final processing before posting.

If there is a significant problem with my monitor, my processing techniques or my imaging gear, I want to know. The main issue for now is that I really understand only a tiny bit when it comes to colour gamuts, monitor technology etc.
One thing I found helpful was buying a ColourMunki monitor callibrater. Its easy to use and calibrates the colours of your monitor. It wasn't that expensive. But this is not really a colour calibration issue as more of a dynamic range issue.

Greg.
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Old 01-12-2015, 08:10 AM
cfranks (Charles)
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Ray,

If you are interested, I have a Spyder 3 display calibrator that I could pop in the mail for you to borrow. You could see directly what effect various calibration parameters have on your image. Return it when satisfied etc.

Charles
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Old 01-12-2015, 08:34 AM
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Greg,

Were you looking at Ray's image in a web browser when you saw the blotchy background? Can you try this test image to see if it is doing colour management?

http://petapixel.com/assets/uploads/2012/06/S2fzq.jpg

Yellow car = colour management enabled. Purple car = no colour management.

Cheers,
Rick.
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Old 01-12-2015, 12:55 PM
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Its showing as a yellow car.
What is colour management? Is that a setting in my laptop or in the image?

Greg.
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Old 01-12-2015, 01:39 PM
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Quote:
Originally Posted by gregbradley View Post
Its showing as a yellow car.
What is colour management? Is that a setting in my laptop or in the image?

Greg.
Thanks, Greg. That's not the problem then...

Colour management relies on a number of things. In the case of an image being displayed on a screen it requires an image with an ICC Profile, an application that implements colour management and that has it enabled, and an accurate profile for the display device.

Cheers,
Rick.
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Old 01-12-2015, 04:00 PM
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Quote:
Originally Posted by gregbradley View Post
One thing I found helpful was buying a ColourMunki monitor callibrater. Its easy to use and calibrates the colours of your monitor. It wasn't that expensive. But this is not really a colour calibration issue as more of a dynamic range issue.

Greg.
thanks for the info Greg

Quote:
Originally Posted by cfranks View Post
Ray,

If you are interested, I have a Spyder 3 display calibrator that I could pop in the mail for you to borrow. You could see directly what effect various calibration parameters have on your image. Return it when satisfied etc.

Charles
thanks Charles, that is very generous - much appreciated. I have decided to buy one myself - almost did some years ago, but pulled out - I think that I really do need one. Thanks anyway for your kind offer.
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Old 02-12-2015, 03:24 PM
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long post

OK, have I got this right? based on reading to date:

If colour management is used:

1. the ICC profile in a file tells what the colour characteristics of the sensor (and image processing system) were when the image was generated.
2. When the data is to be displayed (or printed), the image data is transformed into the colour space of the display device by way of information in the ICC profile of the display (or printer). Thus, this profile contains information on both the characteristics of the display and of the gamut to be displayed. For true representation of the original data, this gamut should be as close as possible to that of the original sensor, so it must be carried over from the original file header. The ICC profile for the display is used to establish LUTs that translate between numerical image values and screen pixel brightness, so that what shows on the screen is a true representation of the image. The LUTs can reside in the monitor, in the PC display hardware/software or possibly even a bit of both.

This process means that the final display should be similar in dynamic range and colour to the original scene (within the limitations of the display technology)

However:

Windows supports colour management, but does not require it - some windows software uses it, some doesn't. If colour management is not used, what you see on the screen is pot luck and will depend on a reasonable alignment between sensor characteristics and those of the display system.
If a display does not have a properly defined ICC profile, but colour management is used, a default profile may be assigned, based on an sRGB gamut and "typical" LCD display. This may be a fair way from providing a true rendition of colours. The only way to get a true profile for your display is to use a hardware calibrator.
The sRGB gamut is widely used (on the internet) and is generally quite effective in reproducing most real colours on video displays. It was initially developed to support typical CRT displays and covers less colour space than the NTSC or AdobeRGB gamuts (eg 72% of NTSC). LCD screens without colour management may only very roughly approximate CRT characteristics - particularly some laptop displays where energy is limited and unimpeded background LED light will be used as white, regardless of the colour temperature. Thus a generic sRGB assumption may be of limited use.

As far as I can tell, this means that what I see when I finish processing an image may be a fair bit different from what someone else sees when viewing it over the internet - the chances that the colour/brightness on my screen will exactly match those on any other are remote.

The only exception would be if my data is prepared on a properly calibrated system that supports colour management, saved with a standard gamut and then viewed by another calibrated system (with colour management) using the same gamut. The most widely used gamut is sRGB, so this should be used if possible for transmitting images over the WWW.

Be very grateful if anyone who really understands this stuff would correct the above. Thanks, ray

Last edited by Shiraz; 02-12-2015 at 04:48 PM.
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Old 02-12-2015, 07:02 PM
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72% of NTSC, as they say, there's your problem.

A good color balanced IPS monitor should be around 90%

My sons cheap TN monitor does 72%.
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Old 02-12-2015, 07:28 PM
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thanks very much Trevor.

I had assumed that the 72% NTSC spec meant that it does full sRGB but not anything broader (NTSC etc). Since I only intend to post on the internet, where sRGB is the standard, would a wider gamut help? According to EIZO, it might be a hindrance, but I have no way of checking. I am wondering if the reason why some are seeing blue background noise, when I see little, might be because they are using the native gamut of their high quality broad-gamut monitors to display a limited gamut sRGB image. does that make sense?

from EIZO: "For purposes requiring accurate color generation, an LCD color monitor lacking any color-gamut conversion function but having a wide color gamut can actually be a disadvantage in some cases. These LCD monitors display each RGB color mapped to the color gamut inherent to the LCD panel in eight bits at full color. As a result, the colors generated are often too vivid for displaying images in the sRGB color gamut (i.e., the sRGB color gamut cannot be reproduced accurately)".

Last edited by Shiraz; 02-12-2015 at 08:06 PM.
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Old 02-12-2015, 07:57 PM
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Hi Ray,

Quote:
Originally Posted by Shiraz View Post
Since I only intend to post on the internet, where sRGB is the standard, would a wider gamut help?
I use a wide gamut monitor mainly because I want to be able to produce vivid prints and most decent printers have a gamut that is not a subset of sRGB. I suspect it is also useful to exceed the bounds of sRGB while processing and then bring it down to sRGB when finishing off the image but I don't have any firm proof for this (though I do have an image of NCG7009 that just dies when transformed to sRGB - all the subtle colour details disappear.)

Quote:
Originally Posted by Shiraz View Post
from EIZO: "For purposes requiring accurate color generation, an LCD color monitor lacking any color-gamut conversion function but having a wide color gamut can actually be a disadvantage in some cases. These LCD monitors display each RGB color mapped to the color gamut inherent to the LCD panel in eight bits at full color. As a result, the colors generated are often too vivid for displaying images in the sRGB color gamut (i.e., the sRGB color gamut cannot be reproduced accurately)".
That's an interesting idea. I presume they are saying that Eizo high end wide gamut monitors are fine but cheap ones are not My NEC certainly doesn't have problems with sRGB but it has a 14-bit LUT and all mod cons.

I was planning to respond to your post above but need to get my thoughts in order and finish doing work stuff so it might not be tonight...

Cheers,
Rick.
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Old 02-12-2015, 08:13 PM
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Hi Ray,

That's an interesting idea. I presume they are saying that Eizo high end wide gamut monitors are fine but cheap ones are not
that would be a novel approach from a manufacturer. The point is interesting though - just how do monitors switch gamuts if the LUTs are stored locally? for example, if you have the screen displaying an sRGB webpage and then you open a full AdobeRGB image in a new window, what happens?

Quote:
Originally Posted by RickS View Post
I was planning to respond to your post above but need to get my thoughts in order and finish doing work stuff so it might not be tonight...

Cheers,
Rick.
thanks Rick - there is no rush - sky is clear tonight . Regards Ray

Last edited by Shiraz; 03-12-2015 at 07:39 AM.
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Old 03-12-2015, 08:14 AM
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Hi Ray

I think you are trying to solve a problem that doesn't have a solution. When images are put on the web you have no way of knowing what they will look like on the viewer's monitor.
I use a calibrated Eizo monitor, the ProPhoto colour profile in Photoshop and then print on a calibrated Epson printer. My images, astro and non astro, look like I want them to be, but they don't look the same if I change them to jpeg and send them to the web for someone else to look at.
As an example, I have posted a Ha image of NGC 2070, the Tarantular nebular, on the "Beginners Images" section. All the fine detail is lost, as is the subtle change in contrast due to the change to jpeg. It looks pretty good on my monitor as the original, but is so so on site. Don't forget this is a monochrome image, forget about colour.
In the end I think this hobby is about having images that you can enjoy yourself. If you want others to see them be aware of the pitfalls unless you are willing to send out prints you have made yourself.
It's good fun though and don't we learn a lot on the way.

Cheers

Greg
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Old 04-12-2015, 08:46 PM
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Hi Ray

I think you are trying to solve a problem that doesn't have a solution. When images are put on the web you have no way of knowing what they will look like on the viewer's monitor.
I use a calibrated Eizo monitor, the ProPhoto colour profile in Photoshop and then print on a calibrated Epson printer. My images, astro and non astro, look like I want them to be, but they don't look the same if I change them to jpeg and send them to the web for someone else to look at.
As an example, I have posted a Ha image of NGC 2070, the Tarantular nebular, on the "Beginners Images" section. All the fine detail is lost, as is the subtle change in contrast due to the change to jpeg. It looks pretty good on my monitor as the original, but is so so on site. Don't forget this is a monochrome image, forget about colour.
In the end I think this hobby is about having images that you can enjoy yourself. If you want others to see them be aware of the pitfalls unless you are willing to send out prints you have made yourself.
It's good fun though and don't we learn a lot on the way.

Cheers

Greg
Thanks Greg - yes, looks like you might be right, there is no solution.

I guess the position that I am coming to is that, for posting purposes, I should be using software that has colour management and an sRGB gamut, to compose images on an sRGB capable screen that is running in sRGB mode. This should yield images that will display best on the average PC/laptop. Using any other gamut, either for composing the image or displaying it will yield sub standard results when posting, even though other gamuts may be better for some forms of printing. Would you agree with that?

At this stage, I think that my 6 bit IPS monitor with 8 bit interpolation should be quite sufficient, provided I can calibrate it to ensure that I am getting a reasonable amount of the sRGB gamut. If I get a more capable monitor, I will need one that can be easily switched between gamuts, since sRGB will still be the most accurate for viewing web pages and JPEG images and it will still be best for composing images for posting. From that perspective, does your Tarantula image look any better if you view over the WEB with your monitor switched to sRGB?

regards Ray

Last edited by Shiraz; 04-12-2015 at 09:31 PM.
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