NEC SpectraView native/non-native calibration and minimum brightness

[Frans Waterlander]

Remarks by Andrew Rodney in another thread raise some questions for me, particularly since I will get my new NEC P242W monitor with SpectraView in a couple of days.

I'd like to know the difference between calibrating an NEC SpectraView natively and non-natively. Native mode, as far as I know, is using the full resolution and maximum brightness, meaning no backlight pulse width modulation (PWM) or the max setting for PWM. Calibrating to a brightness less than maximum means for NEC monitors decreasing the duty cycle of the PWM, whether one started in native mode or not. So why would it make a difference? If you already decreased the brightness using PWM, calibrating it to an even lower brightness means that the duty cycle of the PWM needs to be lowered even more. Why would SpectraView have a problem doing that?

I'd also like to know why NEC would recommend to work with 150cd/m^2 or more and where I can find that information. I've used 105cd/m^2 in the past to match my digital darkroom lighting.

[Schewe]

I'd also like to know why NEC would recommend to work with 150cd/m^2 or more and where I can find that information. I've used 105cd/m^2 in the past to match my digital darkroom lighting.

The 150cd/m^2 is actually part of the ISO standard for graphic arts displays...which also talks about the LUX levels for ambient lighting as well as print viewing lighting. In general, you can use pretty much any display luminosity levels as long as the ambient lighting and the print viewing levels are compatible. For example, I work in a brighter display viewing environment and have a GTI digital dimming print viewing lightbox. Instead of 150cd/m^2, I actually calibrate my NECs to 160cd/m^2 with higher ambient lighting (it's not real bright but far brighter than the cave I worked in when I had CRTs instead of LCDs) and I adjust the brightness for the print viewing to match the intensity of the displays.

[darlingm]

I think I know the answer, but someone may correct me.

Natively calibrating an LCD to its darkest cd/m^2 is by setting it as dark as you can by just using the controls.  (i.e. Brightness 0 in the OSD.)

Non-natively calibrating an LCD allows you to go darker by the ICC profile not sending values near 255 to the LCD.

For example, if you had an LCD that natively could only get as dark as 120cd/m^2, but you wanted it to run at 80cd/m^2, the ICC profile could scale down pure white to something around 170/170/170 RGB, instead of 255/255/255.  (Obviously different to handle any color cast, and I'm not sure the cd/m^2 scale is proportional to rgb, so 170 might not be the correct number, but you get the point.)

I also believe forcing a monitor to run darker through your profile can lead to loss of detail, although this could be less of an issue if your display takes higher than 8-bit/channel (24-bit total) from the video card.  (Most video cards max at 24-bit, some professional level cards run at 30, 34, or 48.)  By this, I mean if you want to display rgb 99/99/99 and rgb 98/98/98 next to each other, those *could* visually and measurably come out the same on a display calibrated to be darker through the profile - due to rounding issues. 

[Frans Waterlander]

Jeff, thanks for your reply but it doesn't explain why NEC would advice to use a minimum brightness of 150cd/m^2 (Andrew Rodney's words, not mine).

[Frans Waterlander]

Mike, These NEC displays have no problem going down to way less than 50cd/m^2, so I don't understand what you are getting at.

[darlingm]

Mike, These NEC displays have no problem going down to way less than 50cd/m^2, so I don't understand what you are getting at.

Without a profile or LUT's loaded?  If so, then I'm confused as to what Andrew meant too.

[Frans Waterlander]

Since I haven't receive a reaction from Andrew yet, I looked a little closer at NEC monitor reviews on tftcentral and it apppears that there are certain limitations on certain NEC models and no limitations for other models. Describing such limitations as related to native or non-native mode (or internal) is in my opinion inaccurate and misleading.

The limitations apply to some models and have to do with going below the lowest range of the backlighting adjustment. Some NEC models allow you to lower the screen brightness below the lowest range of the backlighting pulse width modulation (PWM), which causes the red, green and blue sub-pixels to be turned down and drastically lowers the constrast ratio, something to avoid like the proverbial plague. I looked at 6 high end NEC monitor reviews; 2 could not be lowered beyond the lowest setting for the PWM, and 4 could. Here is an overview:
P232W PWM only, 26 through 291 nits
P241W PWM range 106 through 398 nits, can go down to 45 nits at the expense of contrast
LCD2490WUXi PWM only, 158 through 374 nits
PA231W PWM range 44 though 194 nits, can go down to 14 nits at the expense of contrast
PA241W PWM range 106 through 318 nits, can go down to 32 nits at the expense of contrast
PA271W PWM range 70 through 290 nits, can go down to 32 nits at the expense of contrast

So, depending on the model, these NEC monitors can reach low brightnesses of between 26 and 106 nits without compromising contrast and it has nothing to do with native or non-native mode and everything with backlighting PWM.

[ThDo]

I don't get your reference to PWM.

The decrease of contrast (ratio) at lower luminance levels is simple math.

The contrast ratio is a property of a display system, defined as the ratio of the luminance of white to that of black.

So if you decrease the luminance of white the contrast decreases automatically. Whre is here your connection to PWM?

PWM is used to control de brightness of LEDs without getting a color shift (which you would get with manipulating the current).

[Frans Waterlander]

When the brightness of the monitor is varied by means of PWM, the contrast is fairly constant as shown in the tftcentral reviews. It's only when you want to go below the lowest setting of the PWM on some NEC models that the subpixels are choked off, resulting in lower brightness in the brighter areas of the image, but the darker areas don't get much darker, hence contrast suffers. As I explained, some NEC models vary brightness only by means of the PWM, so there is no degradation of contrast and other models have both PWM and below that the choking off of the subpixels with the inherent degradation of contrast.

[Frans Waterlander]

And here is the information on yet another recent model NEC monitor, the P242W. Brightness adjustements are done exclusively through varying the backlighting pulse width modulation (PWM); there is no setting below the minimum PWM setting that could compromise contrast . At the native color temp setting the maximum brightness is 270 nits and the minimum is 37 nits. Nowhere does NEC advice to keep the brightness at 150 nits or more or any other value for that matter.