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LG xxPK750

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LG 50PK750 calibration report/review

Recently I’ve had the opportunity to calibrate and review a few of the new LG PK750 series plasmas at Cleveland Plasma. The 50PK750 that I looked at first impressed me with it’s sleek, svelte appearance. While it’s stylish enough to make other nearby plasmas or LCD panels look chunky or even a bit dated, the edge to edge glass panel does pick up a large amount of sharp reflections in bright rooms.

Included in the PK750’s picture menu are not only the familiar ISF Expert and THX modes, but a new THX mode for bright rooms. That should be an excellent addition, since in the past THX modes have shown potential for great picture quality; but they have lacked the punch to look good in typical living room lighting.

Chris had used the break in DVD for several days, and after seeing how stunning some of LG’s recent models have looked recently like my favorite LH90, we were like a pair of Clydesdales chomping at the bit.
All measurements were taken with either an Eye One Pro meter or a colorimeter profiled to the Eye One Pro on this TV. Attachments 1 and 2 show the 50PK750’s measured performance in THX cinema and THX bright room. These modes come locked from the factory, though it is possible for an ISF or THX calibrator to unlock them and get them fine tuned. With the power save feature turned off, the ISF Expert modes measured very similar to THX Cinema mode shown in attachment 1: the slight red emphasis and yellow pull towards red will cause skin tones to look a bit sunburnt, and the white balance and gamma suggest that dark images will be a bit overemphasized and have a somewhat steel-gray tone. Overall, the ISF and THX cinema modes show a fairly good foundation that, with some additional tweaking, should give an accurate and involving picture.

THX bright room, which I had high hopes for, was a bit of a letdown as tuned from the factory (attachment 2). The red push and yellow skew seen in the other modes were emphasized even more, and the gamma, which already showed a slight emphasis of dark tones, took that idea and ran with it way past the finish line. In fact, the black level was significantly raised and showed a very distracting blue/purple cast. While it can be argued that shadow detail should be emphasized in bright rooms, this takes that idea to the extreme, to the detriment of the picture. Light output was raised, which will help this mode to be more watchable in high lighting conditions. I checked some program material in this mode with the lights on, and in no time I had had enough of the pasty faces and washed out contrast.

I began calibration of ISF Expert mode, which provides a very extensive set of adjustments to fine tune the picture with the proper equipment. In my reviews of LG’s PS60 and PK550, I complained a bit about LG’s choice of either a 20 point or 2 point white balance adjustment: the 2 point is a bit coarse and cannot be used to improve the gamma, while the 20 point is a good idea taken to the extreme, making it very difficult to use and not offering much if any advantage over a more useable 10 point adjustment. Unfortunately for the PK750, the 20 point adjustment does not even come close to functioning properly. In addition to the past problems of the set dimming after being fed the same size pattern (regardless of intensity or color), excessive interaction of the set’s own bright menu, the quirky “dead zone” behavior, and the set’s full field internal patterns being unusable, there was a new potentially fatal flaw: the blue and green were displaced, at different amounts, from the indicated adjustment points. For example: at 60%, only the red adjustment worked as intended. The blue and green had very little to no effect. When the 60% blue control was adjusted, it actually affected the blue at 70%. When the 60% green control was adjusted, it affected the green at 65%. This misalignment gradually changed at different adjustment points, with no misalignment at 5 to 10% up to severe misalignment at 100%. I tried different resolutions, different contrast settings, and both YCbCr and RGB colorspace via HDMI with no change.

The 2 point adjustment worked normally, though with it the white balance could not be adjusted as well as I would prefer, and the gamma could not be fine tuned. There were still different gamma presets to choose from, though.

The set’s black level, measured with a profiled colorimeter that takes very accurate readings at low levels, was approximately .026 fL, and the modified ANSI contrast was 980:1. The PK750’s advanced menu includes color isolation, which is a more accurate way of determining color decoding behavior than the color filters that come with test DVDs. The color isolation showed uneven color decoding with level, which could cause difficulty with properly calibrating the set’s partial CMS (Color Management System) adjustments. Vertical resolution, with 720P, 1080i, and 1080P, was a bit soft; and there was some edge enhancement on vertical lines. Turning edge enhancement on sharpened the resolution and evened out the edge enhancement so it was on both horizontal and vertical lines. Though it seemed like a good tradeoff, I looked at some program material with the edge enhancement on and off, and greatly preferred it off.

The resulting measurements after adjusting the 2 point adjustment and color controls are shown in attachment 3. The red push and yellow skew were eliminated, and white balance was ironed out to a degree. The gamma was still uneven, though the large shadow detail emphasis was reduced.

The most important questions still needed to be answered: Are these issues just techno mumbo jumbo? How does it really look in the end?

The answer, after looking at my familiar Blu Ray program material, didn’t take too long to figure out. Fleshtones looked surprisingly good, with people looking natural rather than pale or sunburnt. I believe that can be contributed to the good accuracy of the red and yellow after calibration. The set looked rich and vibrant in bright scenes; color popped and bright whites jumped out. In fact, I felt that bright whites looked slightly highlighted and exaggerated, which I believe is a result of the high upper end gamma. The picture held stable with no pumping, and it looked smooth without added graininess. Shadow detail looked excellent, with dark objects being quite visible but not too washed out. However, the blacks were not in the same league as a new Panny plasma. That would be most apparent viewing dark scenes with the TV in a dark room. It appeared to me that 1080P/24 was displayed at 60 Hz rather than a multiple of 24, though in most scenes it was hard to tell. Overall, I felt the PK750 was like a richer looking alternative to Panasonic’s S2 plasma.

At a later date, Chris ordered two more PK750’s in for me to check and calibrate, and they both showed similar misalignments in the 20 point white balance. However, there did seem to be a difference with the misalignment at the low end. I ended up spending many extra hours on one, and eventually did get it’s 20 point adjustment done. However, it was not something I am sure I could do every time, and it is not something that could be reasonably expected from professional calibrators until or unless LG gets the misalignment issue resolved. That sample with the successful 20 point adjustment was used in a three way comparison between the PK750, the Samsung C7000, and the Panasonic G25.

Attachment 4 is the PK750 on which I was successfully able to adjust the 20 point wb/gamma adjustment after much frustration. It is not reasonable to expect this until LG fixes the issue, but it shows how much things can improve.

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