Sony PSP and Nintendo DS Lite

LCD Shoot-Out

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corp.

Copyright © 1990-2006 by DisplayMate Technologies Corporation. All Rights Reserved.

This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated

Into any other work without the prior written permission of DisplayMate Technologies Corporation

 

Article Links:  Overview  MP3 and Video Players  Smart Phones   Game Consoles

Printing: If your browser is improperly printing some pages with text cutoff

 on the right edge then either print in Landscape mode or reduce the font

size (View Menu - Text Size) and margins (File Menu - Page Setup).

 

Introduction

Although the Nintendo DS Lite and Sony PSP (Play Station Portable) are primarily gaming consoles, they both can be used for looking at slide shows of digital photos and watching movies and videos. But, how good are their small screens? Are they toys, pretentious devices, or high quality displays that can produce excellent picture quality comparable to your HDTV or computer monitor? And how do they compare to the players and smart phones in Part I and Part II? To answer these questions I used the same high-powered analysis methods we use for testing and evaluating high-end HDTVs at DisplayMate Technologies. We’re going to find out how worthy these little devices are…

 

The Consoles

The Nintendo and Sony consoles are both very innovative handheld portable devices. The PSP was designed from the ground up as a multimedia console, with full support for photos, videos, and movies via Flash memory and small DVD-like UMDs (Sony’s proprietary Universal Media Discs). But, unlike Sony, Nintendo has concentrated almost exclusively on gaming for the DS Lite, although a small selection of cartoon movies are available via a compatibility mode with the earlier Game Boy Advance. As a result, a decent size cottage industry of hackers has arisen to supply Flash memory based games, photo viewers, and video/movie players. With the DS Lite this is accomplished by using an adapter with Flash memory that connects to the console as a game cartridge. There are a number of such products available. We used the M3 Adapter (specifically the M3 Perfect with Passcard 3 for the DS Lite, which costs about $100). It works well, but there is virtually no documentation or support.

 

Table 1 lists the most important display specifications for the consoles. The DS (Dual Screen) Lite has two identical LCD screens. A Touchscreen is included with the lower main screen.

 

Table 1 – Display Specs

 

Don’t be turned off by the relatively low resolutions of these displays, because it is the pixel density, or Dots Per Inch, DPI, that determines how sharp their images appear, and these are relatively high DPIs. For reference, a 19 inch LCD monitor has a DPI of 86. The number of Screen Colors that a display can produce is frequently misinterpreted as an indication of its color gamut, the range of colors that it can produce. It has nothing to do with the gamut, but rather specifies the number of possible intensity levels for each of the red, green and blue primary colors, which can vary from 32 to 256 levels. While the DS Lite supports 6-bits or 64 levels per color, test patterns show that the M3 Adapter only provides 5-bits or 32 levels per color, which is 32K Screen Colors. In principle, displays with fewer intensity levels produce a less smooth image with more visible contouring, but the effect is less noticeable at higher DPIs.

 

LCD Panel Performance

Before we can evaluate the picture quality of the consoles we need to measure the performance of their LCD panels for Brightness, Contrast, and Viewing Angles. The results shown in Table 2 were made with a laboratory spectroradiometer. See How We Test for technical details and explanations of the measurements. The results are color coded based on the relative performance of all 11 players, phones and game consoles tested for this 3-part series. Green means excellent or significantly better than the other units; red means poor or significantly worse than the other units; and yellow means mediocre performance. The color coding makes it easy to see trends among all of the units.

 

Table 2 – LCD Brightness, Contrast and Viewing Angles

 

Brightness and Contrast:

Peak Brightness is very important in bright ambient light viewing conditions (the brighter the better) but is not important for low ambient light viewing. The two screens on the Nintendo have very similar performance. Both the DS Lite and PSP have four user selectable screen brightness levels, but on the PSP the highest is only available when using its AC power adapter. The peak values that we measured for the PSP are about 30 percent lower than what Sony specifies on its official PSP website. The most likely explanation is that manufacturers frequently publish the brightness of the LCD panels by themselves, without the exterior dark screen layer that helps to lower screen reflectance (below), but this layer also attenuates the viewable brightness of the panel.

 

Black Level Brightness is the residual dark glow that the screen (and each pixel) gives off when it is supposed to be producing true black. It is distracting and also washes out both the contrast and color saturation of the dark portions of the image. The Contrast Ratio tells you the range of brightness that the display is capable of producing. The larger the better, but it’s only relevant for low ambient light viewing conditions due to reflections off the screen (next). The PSP and DS Lite have the highest Contrast Ratios of all of the mobile displays we tested.

 

Performance under Bright Ambient Light:

When these units are used in bright ambient light the screen can’t be made as dark because it reflects a certain percentage of the room light. This washes out the images by reducing contrast and color saturation, and you’ll also see a distracting reflection of your face as well. We measured the Screen Reflectance, which is the percentage of ambient light reflected by each unit. The lower the better. The Main Screen on the DS Lite, with a Touchscreen, has a noticeably higher reflectance than the Top Screen. The Contrast Rating for High Ambient Light is a measure of the contrast you’ll see under high ambient lighting conditions. It is simply the Peak Brightness divided by the Screen Reflectance value in the Table. Again, the larger the better. The DS Lite and PSP performed in the middle of the pack, with 7 of the 11 units falling in their 9 to 13 range.

 

Viewing Angles:

The brightness, contrast, and color saturation that you see on the screen varies significantly with your viewing angle. It has a major impact on image and picture quality. If you’re watching by yourself, the Forward Tilt Viewing angle will vary depending on how you hold the unit. If you’re watching in a group, people to the left and right of the screen will be positioned with a Horizontal Side Viewing angle. Table 2 lists the Contrast Ratio for a 15 degree forward tilt of the screen, which is the largest angle a single viewer is likely to use. Table 2 also lists the Contrast Ratio for Horizontal Side Viewing at ±45 degrees, which is roughly what a person sitting next to the central viewer will see. These Contrast values provide a good measure of how the viewing experience varies with angle.

 

The PSP performs very well with side viewing for multiple viewers, tying for first place among all of the mobile displays, while the DS Lite is effectively limited to a single viewer at a time, which is consistent with its official role as a handheld gaming console. Because of the large change in Contrast Ratio with Tilt Angle for the DS Lite, the positioning of the hinged Top Screen can significantly affect image quality, although it’s not as noticeable when viewing the bright and highly saturated color images that are used in most games.

 

Image and Picture Quality Ratings

An LCD screen with low ratings in Table 2 can still wind up looking quite good with the right color scheme because color can be used to enhance the visual contrast in the menu screens and the artificially colored game environments. That’s how many high DPI screens can appear gorgeous. But that technique can’t be used with photos and videos.

 

Gray Scale and Picture Contrast

The image and picture quality of any display depends on its gray scale and the saturation of its primary colors. The gray scale describes how the brightness of image pixels varies between the black and white extremes and determines the contrast within an image. Too much is just as bad as too little. Figure 1 shows the gray scale measured for each console. See How We Test for details and explanations of the measurements. The differences in gray scales among all eleven devices tested for this series are striking and explain much of the differences in picture quality that we witnessed in the viewing tests.

 

    

  Figure 1. Gray Scales          Figure 2. Primary Colors

Click to enlarge                       Click to enlarge

 

These results are summarized in Table 3 by listing the picture contrast, gray scale compression, and gamma for each unit. Compression of the gray scale near its maximum intensity makes the picture look overexposed. The lower the better. Gamma specifies the steepness of the gray scale and the amount of Picture Contrast, which by industry standards should have values between 2.2 and 2.5, with the value 2.2 used in professional video production studios.

 

The PSP gray scale is outstanding and virtually perfect. This gray scale performance is one of the “secrets” of Sony excellence in television, a lesson that few other manufacturers have learned. It’s impressive that Sony has extended this to the PSP. The DS Lite also has a smooth and straight gray scale, but the slope is very low, reducing its picture contrast noticeably. (Near the middle of the gray scale the brightness is 50 percent higher than what it should be.) It’s impossible to say whether this is due to the M3 Adapter or the DS Lite without reverse engineering their firmware.

 

Table 3 – Image and Picture Quality Ratings

 

Color Saturation and Gamut

The colors in all color displays are produced through a combination of three primary colors: red, green and blue. The primaries need to be strong and saturated in order for the displays to be able to reproduce a wide gamut of colors. Too little saturation and the pictures will look flat and pastel-like, too much saturation and the pictures will look gaudy. We measured the primary colors with the spectroradiometer. Details are shown in Figure 2 and summarized in Table 3 by comparing the Color Gamut of each console to that of a standard High Definition TV or sRGB computer monitor. The closer to 100 percent the better. The Nintendo DS Lite and Motorola Q (Part II) have largest color gamut of all the mobile devices tested. All mobile displays have a reduced color gamut, which can be compensated with proper processing in the device. The PSP, unfortunately, demonstrated weak color saturation in all of the viewing tests (below).

 

Reference and Optimized Photos

The consoles aren’t delivering anywhere near the image and picture quality they are capable of producing. To demonstrate this we’ve produced two sets of photos for each unit: a standard Reference Photo that displays correctly on a calibrated HDTV or computer monitor, and an Optimized Photo that has been mathematically processed based on the lab measurements to improve picture quality. On the DS Lite you will see improved picture contrast and on the PSP improved color saturation. Links for each unit are included in Table 3. Download both the Reference and Optimized photos and compare them to each other and to full resolution versions of the Reference Photo for HDTVs (1280x720) and LCD computer monitors (1280x1024). A thumbnail of the Reference Photo is pictured at left. Left click the links to view on your current display, right click to download the image files. Note that the Optimized Photos are modified for the specific consoles, and will appear to have incorrect gray scales and color on other displays.

 

Videos

All videos are digitally compressed and the resulting picture quality depends critically on how well this was done when the material was recorded. Within the unit, video images are generated by an extra layer of software that decodes a stored video data stream. After this processing, it is handled in the same way as the photos and other images, so the video picture behaves exactly as in the measurements above. In order to view the highest video picture quality that each console can produce, we used the highest video data rates specified by each manufacturer. The optimum video encoding parameters used for the picture quality tests are listed in Table 3.

 

On the PSP a fair selection of movies is available on UMD. They offer DVD-like quality, but at the lower 480x272 native resolution of the console. The PSP can also play videos from Flash memory, but Sony has limited their resolution in firmware in order to promote the sale of UMDs and reduce piracy. The maximum permitted resolution is either 320x240 or 368x208 for widescreen, both of which have only 59 percent of the total number of pixels available at the native resolution of the PSP.

 

On the DS Lite, Majesco Entertainment offers a small selection of cartoon movies and TV shows that play from Game Boy Advance cartridges. They are excellent for small children, but are heavily compressed with a small color palette and low frame rate. A major attraction of the M3 Adapter is that it can play videos stored in Flash memory at the native resolution of the DS Lite. The M3 Adapter’s own player does not perform as well as the freeware MoonShell package that runs on the adapter (but the M3 photo viewer is excellent and much better than the MoonShell photo viewer, which produces image artifacts). The best video encoding for the MoonShell is provided by the freeware program BatchDPG, but some objectionable on-screen false contouring artifacts are still seen from all of these encoders and players.

 

Viewing Tests and Final Grades

After the extensive lab tests it was time to see how well the consoles would perform visually with real photos and videos. So, for the Shoot-Out style Viewing Tests, we compared all eleven tested units simultaneously, side-by-side, showing identical content and comparing them to each other and to a carefully calibrated digital HDTV connected to a PC. I used a large selection of challenging photos that we have for evaluating HDTVs. For video picture quality I used a number of movie clips including The Matrix (which has lots of dark content and a subtle green caste that is difficult for displays to reproduce accurately) and Seabiscuit (which has lots of colorful outside scenery and great facial close-ups).

 

Table 4 provides the results. For the grading and rankings I carefully arranged all of the units until they were ordered from best to worst picture quality, left to right. The evaluations are based on ideal viewing conditions with no ambient light and perfect face-on (zero degree) viewing angle. Each display was scored based on how close it came to delivering an ideal picture, so its screen size, brightness, and pixel count are not part of the grade. Looking at photos and videos on all eleven screens at once was an amazing experience. The range and differences in picture quality were staggering.

 

Table 4 – Shoot-Out Results and Grades

 

The DS Lite and the PSP performed roughly in the middle of the 11 mobile units tested for the series. A major issue for the PSP is its weakness in color saturation, which was clearly evident in the photos, and in both the UMD and Flash memory movies and videos. It was also hurt in the Ratings by the firmware restriction on the resolution of videos played from Flash memory, which degraded them to a noticeably fuzzy appearance on the (comparatively) large 4.3 inch screen. The DS Lite performed well beyond my initial expectations. All of the official Nintendo content is based on artificially colored cartoon-like images, so I wasn’t sure how well it would handle realistic photographic images with delicate colors and gray scales. It’s clear that Nintendo has engineered the DS Lite to do a lot more than its present marketing suggests. The 256x192 resolution screen has only two-thirds the number of pixels as the most popular 320x240 mobile screens, but the images appear surprisingly smooth as a result of the relatively high screen pixel density, which is 64 percent greater per square inch than 19 inch LCD computer monitors. Even with the current aftermarket offerings it already performs better than most of the MP3 players in Part I, including the Apple iPod. With some additional upgrades and tweaking the DS Lite should have no trouble evolving into an excellent mobile multimedia player. There are some indications that Nintendo is already moving towards expanding its multimedia offerings for the DS and DS Lite, which have total worldwide sales of over 25 million units.

 

Much of the reduced image and picture quality of the mobile devices is due to sub-optimal processing within each unit. The Optimized Photos (available via links in Table 3) demonstrate the picture quality the units are capable of producing when mathematical corrections based on the lab measurements are applied to the image files. You can download them and see for yourself if you have one of the tested units. The bottom row of Table 4 provides the image and picture quality ratings based on the Optimized images. When viewing them, the differences between displays become relatively small and all of the units deliver very good to excellent picture quality. Hopefully, the next generation of devices will improve their software/firmware processing and produce this kind of picture quality on their own.

 

Article Links

Series Overview

MP3 and Portable Video Players

Smart Phones

Handheld Game Consoles

How We Test Mobile Displays

 

About the Author

Dr. Raymond Soneira is President of DisplayMate Technologies Corporation of Amherst, New Hampshire, which produces video calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers. See www.displaymate.com. He is a research scientist with a career that spans physics, computer science, and television system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from Princeton University, spent 5 years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested, and installed color television broadcast equipment for the CBS Television Network Engineering and Development Department. He has authored over 35 research articles in scientific journals in physics and computer science, including Scientific American. If you have any comments or questions about the article, you can contact him at dtso@displaymate.com.

 

Copyright © 1990-2006 by DisplayMate Technologies Corporation. All Rights Reserved.
This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated
into any other work without the prior written permission of DisplayMate Technologies Corporation