Calibrated Settings
luminance (cd/m2)	118
Black Point (cd/m2)	0.17
Contrast Ratio	694:1

I calibrated the screen using the LaCie Blue Eye Pro software package and hardware colorimeter. During the process, the OSD settings were adjusted, forming a small part of the overall calibration proceedings. Brightness was adjusted down to a value of 17, contrast was reduced to 65, and RGB values were changed to 251, 235 and 242 respectively. The calibration process then automatically makes adjustments at a graphics card Look Up Table (LUT) level, before creating and activating an ICC profile. There is no hardware level LUT correction with the LP2475W, which some premium colour critical screens in this sector do offer. Immediately to the naked eye you could feel the difference, with the main obvious adjustment being the far more comfortable and sensible luminance setting. Colours also looked more even to the naked eye.

Testing with the colorimeter confirmed our initial impressions. Luminance was now a far more comfortable 118 cd/m², gamma was corrected perfectly to 2.2 and colour temperature was now less than 0.5% out at 6503k. Since we altered the OSD brightness control during the manual calibration stages to 17%, the automated LUT adjustments didn't need to alter the luminance much. We already knew from our contrast stability tests that a brightness level of around 10% was optimum for 120 cd/m². With this adjustment, black depth was improved quite nicely from the default 0.45 cd/m² to a very impressive 0.17 cd/m². This is the best result we have tested from an IPS based screen, and a static contrast raito of 694:1 is very admirable. It looks like finally IPS panels might have overcome their main traditional weakness and can now offer decent black depth. Subjectively, it was impossible to detect only the first 2 shades of grey on the scale from 0 - 255 (255 being pure white). I followed the useful tests here, where the first square you could distinguish on the LP2475W was number 3 (just).

Impressively, the calibration also improved colour accuracy no end. Average dE was now only 0.3, and maximum was  down to 0.5. This was a massive improvement, and actually the best colour accuracy results we have obtained in our reviews! This even beats the Hazro HZ30W which recently became our champion in this regard with average dE of 0.3 and maximum of 0.8.

Testing the screen with various colour gradients showed smooth transitions both horizontally and vertically, and no real sign of even slight gradation. There was certainly no banding issue here.

 

If I compare the colour accuracy results of the LP2475W with the other 24"+ sized screens we have tested, I see the above graph. As you can see, while the default colour accuracy overall was not that good, the calibrated results were excellent. The average dE results before and after were actually identical to the Hazro HZ30W, but the HP LP2475W had the slight edge after calibration as we have discussed above. All in all, calibraiton was a great success. You can be confident of some very good colour rendering capabilities from this screen, but you are going to have to invest in a hardware colorimeter if you want the best from it.

If we compare the calibrated black depth of all the 24"+ models we have tested, you can see the LP2475W performs very well here. The results here are perhaps not what one might expect in the battle of TN Film vs IPS vs PVA vs MVA however! The best black depth after calibration we have here is from the TN Film based (and very cheap) Samsung SM245B (0.16), only just ahead of the H-IPS based LP2475W (0.17)! Who would have thought that TN Film and IPS technology would beat VA matrices in this regard?! True, VA panels, particularly PVA panels, are more consistently impressive in terms of black depth, but with advances like this in H-IPS, and particularly TN Film, it seems PVA panels could be getting a run for their money very soon. The best performing PVA panel here was that used in the Dell 2408WFP (0.18), with the ViewSonic VX2435WM representing the S-MVA generation (0.22). I was suitably impressed with the LP2475W in black depth, an area where I previously felt IPS was lacking.

 

 

Viewing Angles

Above: Viewing angles shown from front and side, and  from above and below. Click for larger images

The viewing angles of the LP2475W were very good, as one would expect from an H-IPS based matrix. The field of vision was wide in all directions, and the technology was free of the obvious contrast shifts vertically of TN Film, and the off-centre contrast shift of VA panels. IPS is widely regarded as the choice for colour critical work because of its wide viewing angles, and the LP2475W did not disappoint in this regard. The panel does not feature an Advanced True Wide (A-TW) polarizer, and so you can spot the characteristic white glow of H-IPS on dark backgrounds, when viewed from extreme angles. In practice, I doubt you'd ever even spot this since you would be very unlikely to view the screen from such an odd position.

 

Panel Uniformity

Measurements of the screens luminance were taken at 35 points across the panel on a pure white background. The measurements were taken using BasICColor's calibration software package, combined with the LaCie Blue Eye Pro colorimeter. The above uniformity diagram shows the difference, as a percentage, between the luminance recorded at each point on the screen, as compared with the reference point of a calibrated 120 cd/m². This is the desired level of luminance for an LCD screen in normal lighting conditions, and  the above shows the variance in the luminance across the screen compared with this point. It is worth noting that panel uniformity can vary from one screen to another, and can depend on manufacturing lines, screen transport and other local factors. This is only a guide of the uniformity of the sample screen we have for review.

As you can see from the above report, the screen was, on the whole, pretty uniform, being between 5% either side of the target luminance of 120 cd/m² across most of the screen. The luminance did drop a little towards the right and left hand edges, and particularly towards the very bottom of the screen. The readings reached as low as 98 cd/m² in the lower left hand corner, but this minor difference was nothing to be particularly worried about.

Above: All black screen in darkened room. Click for larger version

Setting the screen to an all black background and dimming the lights resulted in the above. There was very little difference across the screen that you could detect with the naked eye, and only a very slight leakage of the backlight towards the top right hand corner of the screen. In practice this was almost impossible to detect, and thankfully the screen was free from any leakage along the top and bottom edges, where it can be particularly problematic and off-putting in movies, where black borders are present.

 

Office and Windows Use

The LP2475W offers a nice big 1920 x 1200 resolution to work with, along with a tight pixel pitch of 0.270 mm. This is a tighter pitch than 22"WS, 26"WS and 19"WS format screens, and so text is a little smaller and sharper. There are no preset modes for "office" or "text" which can be handy in varying lighting conditions, and you will definitely want to calibrate the screen, or turn OSD brightness down a lot to get the luminance to a comfortable level for use. There is no analogue interface so I cannot compare that to the digital option. The DVI offered a very crisp and clear image, with sharp text and very good picture quality.

The screen resolution is ideal for side by side split screen working, and the wide range of ergonomic adjustments means the screen can be easily positioned to a comfortable level. The rotate functionality might be handy for some people, but at this screen size I feel it is perhaps a little gimmicky. Height and tilt adjustments are invaluable however.

 

Responsiveness and Gaming

The HP LP2475W was tested using the chase test in PixPerAn, a good bit of software for trying to quantify differences in real terms responsiveness between monitors. As a reminder, a series of pictures are taken on the highest shutter speed and compared. The images below show the best case example on the left hand side, and the worst case example on the right hand side. This should only be used as a rough guide to comparative responsiveness but is handy as a way of keeping a constant test of each screen.

6ms G2G LG.Display H-IPS panel


5ms G2G LG.Display H-IPS panel
 

The LP2475W uses LG.Display's latest 24" H-IPS panel, the LM240WU4. The panel only went intro production in Q1 of 2008 and is so new that it is not even listed on their main module page. Details of the panel are instead available in their latest product catalogue, and in our panel parts database (of course). The module is their latest generation of IPS matrix, and sports a specified response time of 5ms G2G. The LP2475W actually has a specified response time of 6ms G2G, and there's not really much explanation as to why there is a discrepency here. The LP2475W is the first model we have seen which uses this new panel, and perhaps HP have re-measured the response time themselves to provide a figure for their spec list? Regardless, the LM240WU4 is LG.Display's latest generation of H-IPS and so users might expect some top performance as a result.

The H-IPS panel used features Response Time Compensation (RTC) technology, widely used nowadays to boost the response time of transitions across the grey range. These transitions are far more common in practice than a full black > white change, which was previously the fastest response time of an LCD display before these technologies were introduced. As such, a G2G response time is far more suitable for understanding the potential responsiveness of the panel in practice than an ISO black > white response time is.

In the above tests, the LP2475W performed very well. It remained very close to the Hazro HZ24W in these tests and we've already touched on the fact that the panel is 5ms G2G rated, so there is no real reason to separate the Hazro and HP models here, despite their quoted spec. The Hazro HZ24W actually showed a slight white halo-ing behind the moving car, indicating a slight over-shoot of the RTC impulse. This can be fairly common on heavily overdriven displays, and is down to the RTC control being slightly off. It was hardly noticeable in practice, but our tests capture this a little bit in the best case (left) image.

In contrast, the LP2475W didn't show any of this, but did show a slight dark trail behind the moving car. This was evident if you looked closely at the moving image, even without capturing it with the camera. You can see this dark trail behind the speech bubble and the yellow man's head in the above images. This reminded us of an issue we looked at a little while ago with the Dell 2407WFP-HC where an 'overshoot' of the RTC impulse was causing some very obvious inverse ghosting artefacts. I tested the screen in a similar way to how we tested the 2407WFP-HC and saw some slight black trailing behind a white mouse cursor, as it moved across a dark grey background. I don't want to make too big a fuss of this, since I don't feel that it is nearly as obvious or distracting as it was with the 2407WFP-HC - which was effectively discontinued because of this issue. It is worth noting in this review since you can spot the dark trailing image in the PixPerAn tests. Whether this is more of less distracting than a white trailing on other screens is down to the user, but in practice it was pretty hard to spot really.

6ms G2G LG.Display AS-IPS


5ms Samsung TN Film

6ms G2G Samsung S-PVA

I've included the same PixPerAn tests for the Samsung SM245B, Dell 2408WFP and NEC 20WGX2 (our reference monitor for these tests) so you can compare. As you can see, the HP LP2475W was not far behind the performance of the NEC, providing you discount the RTC overshoot artefacts we have discussed above. The Samsung SM245B uses a non-overdriven TN Film panel and the difference is quite obvious. The 6ms G2G Dell 2408WFP is a fair bit slower than some other S-PVA panels from the same generation, but I have included it here since it is a very popular screen right now.

The screen thankfully features a wide range of hardware level aspect ratio control, accessible via the OSD menu. There were options for "fill to screen", "fill to aspect ratio" and "one to one". I tested all of these using various gaming resolutions and they seemed to work nicely without issue. Testing the 1:1 aspect ratio mode with external devices using the main HD resolutions (720 and 1080) showed they were scaled properly and with no stretching vertically or horizontally.

As usual I tested the screen in clone mode with a CRT to determine the level of input lag. This is something which can put off some gamers and is a delay between graphics card and monitor output. By hooking up a CRT you can show that  the LCD lags behind somewhat, which can affect users in some situations where they rely on the screen image being as fast as their inputs (e.g. fast FPS shooting games). Often, input lag is very low and probably wouldn't represent too much of a problem in real terms.

The HP LP2475W performed pretty well in this test, with an average input lag of 25ms being recorded. The input lag ranged from 10 - 40ms but never got above or below this. The 25ms on average is pretty good and represents very little problem in practice, especially if you compare it to the results of other 24"+ models. It's not quite as good as the Samsung SM245B, Hazro HZ30W or Hazro HZ26Wi (all at 7.5ms average), but remains a long way ahead of some very popular 24" screens such as the Dell 2408WFP A00 (64.1ms) and Samsung SM245T (52.5ms).

 

Movies and Video

The following summarises the HP LP2475W's performance in video applications:

• Large 24" screen size and widescreen aspect ratio make it great for watching movies

• Large 1920 x 1200 resolution support for high definition content (supporting 1080p)

• The resolution can be a problem however since any SD content needs to be scaled up, and the resolution means any imperfections and pixelation are accentuated even further. Not necessarily a good screen for watching anything from close up

• Wide viewing angles thanks to the H-IPS panel, good for several viewers watching at once

• Very good black depth mean detail in darker scenes is not lost. Very good in this regard for an IPS matrix

• Decent panel responsiveness ensures no ghosting and minimal blurring in fast moving scenes. Any slight inverse RTC overshoot not apparent in video applications

• Panel uniformity is good overall. No obvious leakage and no problems along top or bottom edges where it is most apparent in movies with black borders

• HDCP is strangely not listed in HP's specification for the LP2475W which could cause problems for people wanting to watch encrypted content. I tested the screen however with a Blu-Ray source which played fine over both DVI and HDMI. I don't have other sources to test, but it looks like HDCP is included after all

• HDMI, DisplayPort, component, composite and S-video interfaces provided for connecting external devices

• Noise is noticeable due to the screen size and resolution, and particularly apparent with low definition content. You need to sit a fair distance away to get away from this

  

Conclusion

Overall I was very impressed by the performance of the LP2475W. While default colour accuracy was pretty poor, once calibrated the screen offered the best colour results we have seen in our reviews. Black depth was excellent for an IPS matrix, and even out-did many PVA matrices we have tested! These were very positive improvements for IPS technology, and hopefully this is a sign of things to come. The screens massive range of ergonomic adjustments and interfaces was also nice to see, and the HP had a very "Dell feel" in terms of finish, functionality and features. Responsiveness was very good, but there was some slight RTC overshoot which caused some dark artefacts in practice. However, the decent pixel responsivenss, combined with pretty good input lag, could make this a good screen for gamers, as well as those wanting an excellent all round performer. If you want a 24" monitor, this is a hard one to beat in my opinion. Given the extreme lack of IPS in this sector, HP are probably on to a winner here.