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Samsung LE40M86BD Benchmarks

by Vincent Teoh
15 April 2007

Torture Test Scorecard

Dead pixels None
Screen Uniformity Clouding (reducible to unobtrusive level)
Overscanning on component 2.5%
Blacker than black Passed
Black level Excellent
Black level retention Stable with DNIe off
Primary chromaticity Average
Scaling Average
Video mode deinterlacing Average; jaggies present on waving flag
Film mode deinterlacing 2:3 pulldown only when Movie Plus is on
Viewing angle Gradual drop-off from 45° onwards
Motion blur Mild (normal for better LCDs)
Digital noise Not noticeable at 8 feet
Sharpness Defeatable edge enhancement

Comments

Screen Uniformity

On the first day of testing the uncalibrated Samsung LE40M86BD I noticed faint clouding on blank inputs (nowhere near as bad as our calibrated Sony KDL40W2000 even on its best day). Proper calibration eliminated the problem – as long as I used the correct settings no clouds were visible even during the dark scenes in zero ambient light. That said, the screen unevenness could be seen off-axis (especially close-up).

Reflections

This panel has a reflective glass panel, so if you're buying it you need to treat it as if you're getting a plasma TV. The reflections are not obvious when there's light output from the TV (i.e. when it's on), but during dark scenes it's not hard to see myself and my surroundings on the screen. People have lived with CRTs for years so what's another reflective TV, but before committing yourself you should have proper TV positioning and ambient light control figured out.

Calibration

Samsung LE40M86BD ships with 3 picture modes, the default of which – as expected – is the torching 'Dynamic' mode which showcases Samsung's proprietary DNIe technology. After cycling through all 3 modes, I discovered that with DNIe turned off, only the 'Movie' mode offered white balance controls for greyscale adjustment, so it became the platform from which I calibrated the Samsung LE40M86BD.

Baseline Correlated Colour Temperature (CCT)

cct-1
rgb-1

Without adjusting white balance in the 'Movie' mode, the picture was overly cool (i.e. blue) at lower stimulus (i.e. darker scenes) and mildly warm (i.e. red) at higher stimulus (i.e. brighter scenes).

Calibrated CCT

We proceeded to calibrate the greyscale using the 'White Balance' controls in the user menu with the help of light-measuring equipments. This is what we achieved (no access to service menu was needed):

cct
rgb

As you can see the greyscale tracked fairly closely to 6500k from 20% stimulus onwards, with only a slight dip in blue at higher stimulus. Here's the resultant gamma curve:

gamma

Looked promising, but a closer inspection revealed a deeper problem. Check out the following graph describing the displayed gamma at each percentage stimulus:

gamma-log

What this means is that the Samsung LE40M86BD has skewed gamma tracking: as the input signal level decreases, the image becomes darker than it should be (if you don't understand gamma, all you need to know is that the higher the gamma, the darker the picture); and at the other end as the signal level increases, the image becomes brighter than it should be.

As you can imagine this will have a negative impact on the picture, causing loss of both shadow detail (also known unofficially as "black crush" that – strictly speaking – should be reserved for description of inability to pass below-black data) and highlights (aka "near-white detail"). Ideally the gamma tracking should be as flat as possible throughout the whole stimulus range so that each input signal level generate the proportionate gamma-adjusted brightness intensity. For comparison, here are some examples of recent LCD TVs that do this well (and consequently preserve shadow detail):

w2000
Sony Bravia KDL40W2000
 
xd1e
Sharp Aquos LC42XD1E
 
lxd70
Panasonic Viera TX32LXD70

Part of the reason why this review took so long to complete was that both Colin and I painstakingly explored all the feasible combination of options in the user menu AND service menu to try and flatten the gamma tracking. For dark film fanatics, this can mean the difference between an LCD TV they can live with and one they should avoid.

We measured gamma tracking for each of these settings individually and in combination: "DNIe", "Black Adjust", "Dynamic Contrast", "Gamma", "White Balance", "HDMI Black Level", "Energy Saving", backlight, brightness and contrast and a host of undecipherable options in the service menu. None corrected the skewed gamma tracking, although bumping up the "Gamma" (not to be confused with our measured gamma) brought out a tad more shadow detail at the expense of image contrast.

Baseline Colour Chromaticity

In the user menu of the Samsung LE40M86BD, there are 2 options that can influence colour chromaticity: 'Colour Space' and 'xvYCC'. Samsung's description of the exact function of these controls is vague at best, so we thought we'd use the following CIE chromaticity diagrams to illustrate what happens when each option is selected:

"Colour Space" = Auto & "xvYCC" = Off
cie-baseline
Closer to the ITU-R BT.601 (NTSC) Standard than PAL or 709
 
"Colour Space" = Wide & "xvYCC" = Off
cie-wide
Overshot green adopting a bluish overcast
 
"Colour Space" = Auto & "xvYCC" = On
cie-xvycc
xvYCC colour processing doesn't conform to conventional standards

Calibrated Colour Chromaticity

Some of you may remember how we praised the CMS (Color Management System) on the Pioneer PDP4270XD plasma that allowed us to align the colour points to the exact intended spot on the CIE diagram. The Samsung LE40M86BD didn't quite reach that particular high standard in terms of colour chromaticity:

cie

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