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Samsung LE40A656 Calibration

by Vincent Teoh
5 June 2008

Greyscale

Among the [Picture Mode] presets available on the Samsung LE40A656, "Movie" with the default "Warm2" [Colour Tone] yielded a greyscale that was closest to the D65 standard.

Pre-calibration CCT
Pre-calibration CCT with [Picture Mode] "Movie" & [Colour Tone] "Warm2"
Pre-calibration RGB tracking
Pre-calibration RGB tracking and delta errors (dEs)

Both red and blue components remained too high, which meant that delta errors (dEs) overshot the acceptable threshold of under 4 by quite a noticeable margin. Using the RGB offset and gain controls provided in the [White Balance] submenu, we calibrated the greyscale on Samsung LE40A656 closer to spec:

CCT after greyscale calibration
CCT after greyscale calibration in "Movie" [Picture Mode]
RGB tracking after calibration
RGB tracking and delta errors (dEs) after greyscale calibration

We managed to reduce dEs to below 4 from 20% stimulus onwards, but the sharp-eyed among you may have noticed that top-end blue luminance was starting to clip. To be honest, we could have rectified this by lowering [Contrast] substantially on the Samsung LE40A656, but because this entailed too much sacrifice in peak luminance, we simply left it as it was.

Colour

Three [Colour Space] options are offered in the user menu of the Samsung LE40A656: "Auto", "Native" and "Custom". Contrary to its name, "Native" [Colour Space] actually generated a colour gamut that was more saturated (akin to the old [Colour Space] "Wide"), as you can see from the following CIE charts captured prior to calibration:

[Colour Space] Auto [Colour Space] Native
[Colour Space] "Auto" CIE [Colour Space] "Native" CIE

Because green primary colour point was tilted towards blue with either [Colour Space] "Auto" or "Native", we took advantage of the included colour management system (which became accessible once [Colour Space] was set to "Custom") to fix the colours on the Samsung LE40A656 LCD HDTV.

Post-calibration CIE chart
CIE chart with reference to HD Rec. 709 after calibration with HD source
Post-calibration CIE PAL chart
CIE chart with reference to PAL after calibration with SD source

Even with the luxury of a colour management system (albeit not full-fledged), some compromise in red and green saturation was necessary in order to maintain accurate hues and colour decoding on the Samsung LE40A656. That said, all three secondary colour points were aligned into the correct hues, which will surely have a positive impact on skin tone rendering.

Benchmark Test Results

Dead pixels None
Screen uniformity Clouding reducible to negligible levels
Overscanning on HDMI 0% with [Size] set to "Just Scan"
Blacker than black Passed
Black level Excellent
Black level retention Stable
Primary chromaticity Good after calibration with "Custom" [Colour Space]
Scaling Above average
Video mode deinterlacing Very good; effective jaggies reduction
Film mode deinterlacing Passed 3:2 and 2:2 cadences in all resolutions
Viewing angle Good for an LCD TV (90°)
Static resolution Fully resolved 1920x1080 over HDMI & component
Motion resolution 650 with [100Hz Motion Plus] "High"; 300 when off
Digital noise reduction Acceptable at baseline
Sharpness Defeatable edge enhancement
1080p/24 capability (PS3) Accepts 1080p/24 video signal; no telecine judder
Input lag (rel. to Samsung F96) On par in [Game] mode or over VGA; 30ms slower otherwise

Power Consumption

Default 223 watts
Calibrated 99 watts
Standby 1 watt

Black Level

Believe it or not, calibrated black level on the Samsung LE40A656 was exactly the same as that measured on the Sony W4000, i.e. an excellent 0.05 cd/m2. In a dark room, the blacks on the Samsung LE40A656 LCD television would look marginally – and we do mean marginally – deeper than the Sony W4000 as a result of the enhanced sense of depth and dimensionality conferred by "Ultra Clear Panel". However, in a brighter environment the reverse would be true: the blacks on Samsung LE40A656 would be diluted by glare from its reflective screen (compared to the less shiny Sony W4000).

Screen/ Backlight Uniformity

Our Samsung LE40A656 review sample exhibited some clouding (patches of uneven backlight) on default factory settings, but proper calibration attenuated this to unobtrusive levels. When we put up some dark-grey flat-field test patterns, the sides of the screen also appeared slightly lighter than the middle. To be fair though, this is pretty much within our expectations: no flat panel LCDs we've tested above the size of 40-inch could to this day match the perfect screen uniformity normally found on plasma TVs.

Static Resolution

With "Just Scan" engaged to attain 1:1 pixel mapping without overscan, the Samsung LE40A656 HDTV fully resolved all 1920 vertical and 1080 horizontal single-pixel-wide lines over HDMI and component, though with the latter there was significantly more noise interference when displaying the 1920 vertical lines pattern.

Motion Resolution

Without activating [100Hz Motion Plus], baseline motion resolution on the Samsung LE40A656 LCD TV was measured to be 300 according to Chapter 31 of the "FPD Benchmark Software For Professional" test disc. Setting [100Hz Motion Plus] to "Low", "Medium" and "High" would boost motion resolution to 550, 600 and 650 respectively. Other than the rare instances of strobing between the scrolling lines, we did not notice any significant interpolation artefacts with [100Hz Motion Plus] engaged on the Samsung LE40A656.

Video Processing

Overall video processing on the Samsung LE40A656 flat panel television is a massive improvement over its predecessors, bettering even the latest Sony Bravias including the W4000 series. Among all the HDTVs we've reviewed thus far, only the television sets from Pioneer, Toshiba and LG were able to match/ surpass the Samsung LE40A656's prowess in this area.

For video-based content, the jagged edges in the rotating line, bouncing bars and waving flag test patterns were smoothened effectively. For film-based material, the Samsung LE40A656 correctly detected and processed 2:2 cadence over 576i, and 3:2 cadence over 480i and even 1080i which most TV sets fail to do. And the best news is, all these deinterlacing wizardry took place automatically without requiring any further intervention from users (such as engaging or disengaging "Film Mode" depending on whether the source material is video or film-based).

The quality of scaling/ upconversion was above average... the Samsung LE40A656 managed to present sufficient detail from standard-definition material without looking overly soft or causing excessive ringing. [Digital NR] did a decent job of removing noise from low-quality analogue transmission, but because the picture on screen already looked clean enough at baseline for the most parts, we left it off to avoid the risk of truncating fine detail or introducing motion trails.

Sidenote: Interestingly, when we put up the "HD Noise" test pattern from HD HQV Benchmark Blu-ray disc, the Samsung LE40A656 exhibited a focus-defocus artefact we've never encountered before on other HDTVs. We've shot a video to try and demonstrate the problem:

Youtube's compression permitting, you may be able to see the venation on the orchid petals going in and out of focus, as if a blur filter was being applied in a pulsatile fashion. Probably stemming from an overzealous noise reduction algorithm, this issue was swiftly addressed by Samsung, who has since released a firmware update that eradicated the artefact on our LE40A656 review sample.

4.5 Star Rating: Highly Recommended

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