Pages: [1]   Go Down

Author Topic: Uniformity - what is a reasonable expectation?  (Read 1137 times)

Frodo

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
    • http://
Uniformity - what is a reasonable expectation?
« on: November 20, 2017, 07:50:32 PM »

I vacillated between getting an Eizo or NEC display, but purchased a BenQ SW2700 based on mixed reports, a little larger in size and resolution and a price less than 2/3rds of the 24 inch Eizos and NECs.  I knew that there would be a bit of lottery with the BenQ and, indeed, the first screen was quite bad.  I checked uniformity with an X-Rite i1 Display Pro, using X-Rites Profiler software.  The BenQ screen had good luminance uniformity, but colour uniformity was poor - it ranged from 258K too cool in one spot to 153K too warm in another.

The NZ distributer replaced the screen promptly and without fuss (thanks!).  The second screen is much better, ranging from 84K too cool to 110K too warm (I calibrated the screen to 5500K).  The range is similar at 6000K, but shifted slightly warmer.
The variation in colour is visible on the second screen with critical black and white work (but much better than the first screen).

What are reasonable expectations regarding colour uniformity?
Logged

Frodo

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
    • http://
Re: Uniformity - what is a reasonable expectation?
« Reply #1 on: November 30, 2017, 01:31:58 PM »

BenQ got back to me and provided me with their "Uniformity Test Tool".  This is an excellent piece of software that, with my i-Rite Display Pro, measures the screen in 25 places (compared to i-Profiler's 9) and goes much closer to the edge of the screen. It assesses the screen at white (255, 255, 255), mid grey (127, 127, 127) and dark grey (63, 63, 63).
Their Pass Criteria are:
PV series: Delta E ≦4 & luminance uniformity should be lower than 10%
SW series: Delta E ≦6 & luminance uniformity should be lower than 25%

The screen is within specifications for white. Two cells fail for luminosity in dark grey, but I do not consider the variance to be significant given the low luminance values measured. However, five cells fail in the mid-grey (which is important for black and white work).  All of the five fail on colour (delta E) (one marginally) and two for luminance (although another two are just under 25%). 

This screen is much better than the first I received, but does not meet BenQ criteria. I ahve yet to hear back from BenQ is relation to the results of my measurements.

Logged

ChrisMax

  • Newbie
  • *
  • Offline Offline
  • Posts: 21
Re: Uniformity - what is a reasonable expectation?
« Reply #2 on: December 05, 2017, 07:27:18 PM »

I went thru 4 BenQ SW2700s then decided to spend the extra bucks on an Eizo.  The saying 'long after the price is forgotten the quality is remembered' is so true!  I'm very happy with the Eizo!
Logged

andrewrodney

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 13238
    • http://www.digitaldog.net/
Re: Uniformity - what is a reasonable expectation?
« Reply #3 on: December 05, 2017, 07:57:05 PM »

What are reasonable expectations regarding colour uniformity?
Not sure what's 'reasonable' but you want as uniform purity as possible! Some displays have electronics to aid in this (NEC SpectraView or Eizo come to mind).
Create a doc in Photoshop using Lstar 50/middle gray. Fill the screen in Photoshop, hit F key and Tab key until the entire image is filled with that gray. Ideally, it's gray edge to edge.
I wish I could take a screen capture of my PA272W this way, but that will not work in showing others. I could take measurements from all four corners and the center, produce a dE report. But you really need to do this testing on your end.
BTW, I've heard a lot of not so good reports on the BenQ but have no direct experience. Not sure I want to.  :o [size=78%] [/size]
Logged
Andrew Rodney
Author “Color Management for Photographers"

Tibor O

  • Newbie
  • *
  • Offline Offline
  • Posts: 37
Re: Uniformity - what is a reasonable expectation?
« Reply #4 on: December 06, 2017, 02:42:03 AM »

As my NEC SpectraView is at the end of its lifetime I am in a market for a new display also. As my NEC had issues with hardware calibration after many OS X upgrades I decided to thoroughly study some of the available literature on NEC and Eizo monitors and decided to go with Eizo this time.

In the Eizo literature available at their global site they state "Monitors with EIZO circuitry for digital uniformity compensation achieve a ΔE value of 3 or better relative to the center across a wider area of the screen." They use their proprietary Digital Uniformity Equalizer (DUE) for which they say is "for perfect luminance distribution and color purity" and it should "guarantee perfect brightness and colour purity on the entire display". They explain that DUE "controls all tone values over the entire monitor, pixel by pixel. The effect: color tones appear identical at each point on the screen, without the brightness fluctuations you experience in conventional LCDs. The DUE function also balances out the effects of fluctuations in ambient temperature on the color temperature and brightness. You will enjoy consistently even luminance distribution and perfect color purity. A real plus when touching-up images."

I decided on the CG277 model which shall come with the “Adjustment Certificate”, which describes the factory measurement results of the grayscale and uniformity characteristics for each monitor. Also, if needed you can change the DUE setting yourself.

The DUE settings are explained in the user manual:
- DUE Brightness setting makes the brightness and color of the whole screen uniform without changing the maximum brightness and contrast ratio. The brightness of a high gradation area is not corrected. Select this setting to prioritize the levels of the brightness and contrast over the uniformity in the high gradation area.
- DUE Uniformity setting makes the brightness and color of the whole screen uniform. The brightness of a high graduation area is also corrected so it is uniform. Select this setting to prioritize the uniformity over the levels of the brightness and contrast in the high gradation area.

Note however that any deterioration of display performance caused by the deterioration of expendable parts such as the LCD panel and/or backlight, etc. (e.g. changes in brightness uniformity, changes in color, changes in color uniformity, defects in pixels including burnt pixels, etc.) are not covered under the Eizo warranty.

Hope this helps.
Logged

andrewrodney

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 13238
    • http://www.digitaldog.net/
Re: Uniformity - what is a reasonable expectation?
« Reply #5 on: December 06, 2017, 10:20:16 AM »

As my NEC SpectraView is at the end of its lifetime I am in a market for a new display also. As my NEC had issues with hardware calibration after many OS X upgrades I decided to thoroughly study some of the available literature on NEC and Eizo monitors and decided to go with Eizo this time.
Interesting, never had a single issue on my end, on a Mac.
I have to wonder if this Adjustment Certificate is worth the paper it's printed on. And indeed, NEC and other's provide the same kinds of paperwork.
Logged
Andrew Rodney
Author “Color Management for Photographers"

Tibor O

  • Newbie
  • *
  • Offline Offline
  • Posts: 37
Re: Uniformity - what is a reasonable expectation?
« Reply #6 on: December 06, 2017, 12:59:11 PM »

My situation was the same as described in the Nec Spectra View II FAQ

I will quote the relevant Q and A:

Q: A compatibility issue with the current Mac OS version and my Mac is preventing me from calibrating the display using SpectraView. What alternatives are available?

A: Unfortunately in some cases it may not be possible to calibrate the display directly using SpectraView due to compatibility issues with certain versions of Mac OS or Mac hardware. Such issues are normally out of our control, but we are always working closely with Apple to resolve these kinds of issues as soon as possible. In the interim time, the following solutions may be considered:

1) If possible, calibrate the display on another Mac or PC that is supported. Since the display is hardware calibrated it can be moved to another machine and the calibration will remain valid. Be sure to also copy and associate the ColorSync profile of the display.
2) If the issue is related to a particular version of Mac OS and you have another version of Mac OS installed on another drive partition, restart the Mac with the other Mac OS version, calibrate the display, then switch back to the original Mac OS partition.
3) In some cases, it may be possible to calibrate the display using Windows under Boot Camp on the same machine. If you have an Intel based Mac and have Windows installed on your Mac, try using the Windows version of SpectraView. Note that it is not possible to calibrate the display using Windows running within Mac OS - only Windows running in Boot Camp is supported.
4) Calibrate using a non-hardware based 3rd party calibration package. Such software may have been included with your color sensor or available from the manufacturer’s website.

End of quote.

As I had a specific Mac Pro and Mac OS X combination atuned with my other software I contacted Nec support and they explained that in my case if I wanted to use that combination I would have to bring my monitor to them to change the hardware configuration. This was midway where I changed the machine and the OS. To simplify, I was using Nec with my Mac Pro 1 and Mac OS 1 without any problems and using hardware calibration, but when switching to Mac Pro 2 and Mac OS 2 the hardware calibration no longer worked. Since sending the monitor back to Nec was not monetary doable for me I used only software calibration on the second machine.
Logged

andrewrodney

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 13238
    • http://www.digitaldog.net/
Re: Uniformity - what is a reasonable expectation?
« Reply #7 on: December 06, 2017, 01:02:54 PM »

My situation was the same as described in the Nec Spectra View II FAQ
All I can tell you is my experience using the Mac (since 1988) and multiple SpectraView's (dating 12+ years*) and updating my Mac OS when available to do so: ZERO issues.
*http://digitaldog.net/files/NEC.pdf
Logged
Andrew Rodney
Author “Color Management for Photographers"

Tibor O

  • Newbie
  • *
  • Offline Offline
  • Posts: 37
Re: Uniformity - what is a reasonable expectation?
« Reply #8 on: December 06, 2017, 01:37:00 PM »

Thanks for the info.

However, I already decided on the Eizo CG277 that should come in time for Christmas :) I forgot to mention that in my country we have a direct Eizo dealer and a better support for Eizo monitors than for Nec. I specifically asked the dealer about possible configuration and compatibility issues and he assured me that my configuration is 100% compatible and that in case of any problems I should have they offer on-line distance support. Also, the dealer is just half an hour drive from my studio :)
Logged

Frodo

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
    • http://
Re: Uniformity - what is a reasonable expectation?
« Reply #9 on: December 17, 2017, 04:13:55 AM »

BenQ got back to me and provided me with their "Uniformity Test Tool".  This is an excellent piece of software that, with my i-Rite Display Pro, measures the screen in 25 places (compared to i-Profiler's 9) and goes much closer to the edge of the screen. It assesses the screen at white (255, 255, 255), mid grey (127, 127, 127) and dark grey (63, 63, 63).
Their Pass Criteria are:
PV series: Delta E ≦4 & luminance uniformity should be lower than 10%
SW series: Delta E ≦6 & luminance uniformity should be lower than 25%

The screen is within specifications for white. Two cells fail for luminosity in dark grey, but I do not consider the variance to be significant given the low luminance values measured. However, five cells fail in the mid-grey (which is important for black and white work).  All of the five fail on colour (delta E) (one marginally) and two for luminance (although another two are just under 25%). 

This screen is much better than the first I received, but does not meet BenQ criteria. I ahve yet to hear back from BenQ is relation to the results of my measurements.

BenQ got back to me and informed me that the criteria are only valid when measured at gray 255 (white) and not at gray 127 (mid gray).  I understand that at 255 white, the three colour channels are largely saturated and so there is little scope for large colour variations.  Mid gray would be more sensitive to colour variations and is photographically more important. So I think BenQ's response is a fudge.

I took the readings from the BenQ uniformity tool, entered them in a spreadsheet and saved them as image files for easier viewing.  In the black boxes are the 25 cells that related to the 25 positions in the screen, each for 255, 127 and 63, with the first being colour and the second delta E. 
The first relates to differences in colour from the screen average (BenQ references everything to the central cell) as I think that this gives a better indication of uniformity.  I used four classes: 0-50 (clear) then 50-100, 100-200 and >200 in steadily darker colours.
In the second I have used the delta E figures as generated in the BenQ uniformity tool, with yellow being greater than 3 (which I understand is the Eizo criterion), orange being greater than 4 (the BenQ criterion for PW displays) and red being greater than 6 (the BenQ criterion for my display).
Please note that this is much better than the first display I received from BenQ!!

Delta E is calculated through a complex formula to determine the distance between two colours in a colour space (see: https://en.wikipedia.org/wiki/Color_difference).
But the ability to perceive differences doesn't just depend on the distance between the colours, but depends on the colours themselves.  This is shown in the diagram below that I took from the Wikipedia reference, noting that the ellipses of tolerance contours are shown ten times their actual size.

So uniformity of luminosity is easily and objectively measured and my screen is okay.
But as I found out, colour is more complex.  While I agree with Andrew, uniformity should be as high as possible, but of course there is a cost to this  I believe that my screen does not meet BenQ's own criteria.
Perhaps the best way to judge the screen is the final image taken of the screen a few moments ago.  All I have done is corrected for peripheral illumination and cropped to make the screen rectangular.  I ahve not adjusted colour or contrast.

Is this good enough?

« Last Edit: December 17, 2017, 12:04:47 PM by Frodo »
Logged
Pages: [1]   Go Up