Thursday, April 3, 2008

LC42XL2E Calibration & Benchmark


Like previous Aquos LCD TVs we've reviewed before, the Sharp LC42XL2E does not offer white balance control in its user menu for fine greyscale calibration, so you'll have to make do with one of the five [Colour Temp] presets. Predictably, [Colour Temp] "Low" came closest to the D65 imaging standard:

[Colour Temp] Low CCT [Colour Temp] Low RGB
[Colour Temp] "Low" CCT
[Colour Temp] "Low" RGB Tracking

The picture would look cooler/ bluer in darker areas, but warmer/ redder as the luminance increased. Because the latter tends to amplify the red push colour decoding error (I shall explain this in the "Colour" section) on the Sharp LC42XL2E, you may find the overall image more pleasing if you set [Colour Temp] to "Mid-Low" which serves to counteract the red push although at the expense of even further deviation from D65:

Mid-low CCT Mid-Low RGB Tracking
[Colour Temp] "Mid-Low" CCT "Mid-Low" RGB Tracking

A word on calibrating in [User] mode vs [Movie] mode. Have a look at the following graphs depicting the displayed gamma against luminance in 10% increments:

User Mode Movie Mode
[User Mode] gamma tracking
[Movie Mode] gamma tracking

On the whole, gamma tracking for the [Movie Mode] was smoother and flatter across the luminance range – giving the most natural and realistic-looking rise from dark to light – without straying too far from the desirable 2.22 level. On the other hand, there seemed to be some sort of crude low-end gamma adjustment hard-coded within the [User Mode], resulting in an alarming dip in gamma below 30% stimulus, which would inevitably obscure shadow detail.


When plotted on a CIE chart, the red and blue colour points on the Sharp LC42XL2E were bang on the HD Rec. 709 reference, but green was deviated towards cyan. Because this LCD television lacks any sort of colour management system in the user menu, the best I could do was to attempt to match 2 out of the 3 secondary colour points by adjusting the [Colour] and [Tint] controls:

Pre-calibration CIE Chart Post-calibration CIE
Pre (left) and post-calibration (right) CIE chart with reference to Rec. 709

What these CIE charts does not show you is the amount of colour decoding error on a display device. In the case of the Sharp LC42XL2E, there was noticeable red push which could be attenuated somewhat but not corrected completely by toning [Colour] down.

What is red push?
A colour decoding error that makes red more intense than it should be.

Why does it happen?
To attract buyers on the sales floor, manufacturers like to make their TVs brighter by pushing up the colour temperature (i.e. the picture is tinted blue), which causes skin tone to look unnatural. To make the skin look realistic again, manufacturers introduce red push to neutralise the blue tint. Unfortunately while red push corrects the colour of the skin, it also exaggerates the red in everything else, which is worsened when the hyper-blue greyscale is restored to D65.

How do I tell if my television has red push?
Through filters + colour bar test pattern, colour intensity measurements and/ or real-life programme material.

How can I eliminate red push on my TV?
Generally you can't, unless your TV offers colour decoder control (which very few TVs do, and even then it's usually buried in the service menu). An R-Y attenuator may work for external component video device. Your best bet is to hope that your TV's colour decoding is correct in the first place.

Can I correct red push by adjusting R-Cut or R-Gain?
No. R-Cut and R-Gain are used to adjust the total amount of red that makes up grey... greyscale is a separate matter from colour decoding.

Benchmark Testing

Stuck pixels 0
Screen uniformity Horizontal and vertical "bands"
Overscanning on HDMI
0% in [Dot by Dot] mode
Blacker than black Passed
Black level Very good for an LCD TV
Black level retention Stable if [OPC] & [Active Contrast] off
Colour chromaticities Green primary deviated towards cyan
Colour decoding Red push
Scaling Good
Video mode deinterlacing Good
Film mode deinterlacing Excellent
Viewing angle 60°
Motion resolution
600 with [100Hz] on; 300 when off
Digital noise reduction Effective, with minimal loss of fine detail
Sharpness Defeatable edge enhancement
1080p/24 capability (PS3) Accepts 1080p/24 signal from PS3 – no telecine judder
1:1 pixel mapping Yes, in [Dot by Dot] mode for 1080 source

Screen Uniformity

Previous large-sized Sharp Aquos LCD televisions had been known to suffer from screen uniformity issues manifesting as "bands" of irregular luminance, and unfortunately the Sharp LC42XL2E I reviewed was no different. In our benchmark tests, these horizontal and vertical bands were most obvious when a relatively dark (between 20% to 40% stimulus) full-field grey pattern was put up:


Thankfully in real-life programme material the "bands" were a lot less visible, only cropping up when there's slow camera movement across a lightly-saturated background such as blue sky. Even then anecdotal reports suggest that there may be some band-free units out there due to set-to-set variation.

Black Level

After calibration, the blacks on Sharp LC42XL2E was lighter than that on the Samsung LE40F86BD and Sony KDL40W3000, but still qualifies as very good for an LCD TV. No black level fluctuation took place as long as [OPC] – which automatically adjusts the backlight depending on the amount of ambient light sensed – was not engaged.

Static Resolution

In [Dot by Dot] mode, the Sharp LC42XL2E successfully resolved all the horizontal (1080) and vertical (1920) single-pixel lines over HDMI and component (slightly more noise and interference), as one would expect from a true HD LCD television sold by a major brand.

Motion Resolution

I used Chapter 31 of the "FPD Benchmark Software" to test motion resolution. If [100Hz] was disabled, the Sharp LC42XL2E would perform around the level of LCD TVs not equipped with motion compensation frame interpolation (MCFI), achieving a motion resolution of 300.

Once [100Hz] was engaged, motion resolution on the Sharp LC42XL2E doubled to 600, which is the highest I've recorded on an LCD television to date. Another good news is that the MCFI implementation on Sharp LC42XL2E did not evince as many artifacts as those found on rival LCDs such as the Samsung F86.

Video Processing

The Sharp LC42XL2E fared extremely well in this department: certainly its scaling and video mode deinterlacing were among the best I have seen on an LCD TV.

Film mode deinterlacing was equally impressive. With [Film Mode] set to either "Standard" or "Advanced", the Sharp LC42XL2E without fail detected and processed both 3:2 and 2:2 cadence speedily over 480i, 576i and even 1080i (which very few flat panel sets can do). [Film Mode] "Advanced" however would add a dash of frame interpolation to the picture... I generally recommend against this unless you dig the amateur video feel that it entails.

Mixed edits were handled competently – no combing of scrolling text overlaid upon film content was witnessed. The LC42XL2E's digital noise reduction control can be very effective especially for noisy analogue source, but because I'm a purist who cannot bear the thought of even the slightest loss of fine detail, I left [DNR] off for critical viewing.

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