When we see any HDTV, smartphone, laptop and tablet, we see companies boasting lot of different terms like ‘color gamut’, ‘aspect ratio’, ‘nits’, etc. when speaking about their display. Companies use them a lot as their marketing tool. And they are mostly misunderstood by consumers. So, what they actually mean? Let’s find out.
Screen size – We all know that display size is measured as the diagonal length of the screen. But what actually matters visually is the area (width x height) of the screen. The area can be obtained by squaring the diagonal length. If we observe one thing, a 7 inch tablet (49) has half the area of a 10 inch tablet(100). If you are comparing two devices, it is good to compare areas of the both if you are concerned about display size. The area also depends on the shape of the screen, which is another spec called aspect ratio (below). Lower aspect ratios have larger screen areas for the same diagonal size. For example, a 10-inch, 4:3 Aspect Ratio screen is 12-percent larger in area than a 10-inch, 16:9 screen.
Aspect ratio – This term is used to determine the shape of the screen. This is generally indicated in two ratios, namely 16:9 and 4:3. Some brands indicate the numerical directly as the aspect ratio like 1.78 for 16 by 9. This is obtained by dividing the resolution of your screen. The same is also obtained by dividing the height and width of your screen. The perfect aspect ratio on a display is achieved when both of these match. For example, dividing the Full HD resolution say 1920 by 1080 gives you 1.78 which equals to the aspect ratio of 16:9. Now you have to get the same value if you divide your width and height of the display. This ratio is the standard for viewing wide screen content. Another common aspect ratio is 4:3 or 1.33, which is also the same aspect ratio as content from 8.5 x 11-inch documents. This aspect ratio is better for reading in either Landscape or Portrait modes, but not as good for viewing widescreen content.
PPI (Pixels per Inch) – This is also one of the most talked spec in display tech. This gained popularity when apple started using the term ‘Retina Display’ for its devices. True, the higher the PPI the sharper the image on the screen, but what really matters is the sharpness perceived by your eye and that depends on the viewing distance from the screen (and also how good your vision is compared to 20/20 Vision). So PPI cannot be used by itself, but must be used together with the viewing distance in order to draw any conclusions about visual sharpness, and whether or not it qualifies as a retina display. While the iPhone 7 has an impressive 326 PPI, it is typically held relatively close and viewed from around 12 inches. Larger displays like tablets and laptops are typically viewed from 16 inches or more and need only 215 PPI to appear perfectly sharp with 20/20 Vision (what Apple calls a retina display).
In fact, existing 1920×1080 HDTVs, which have same resolution as this generation mobiles, are viewed from much larger distances. But do you find any difference in sharpness between these two devices? So after a limit, there is no use for you even though the display has higher PPI. Even, higher resolution draws more power from your battery. The only advantage is that if you have a higher resolution display on a mobile, then a full HD video plays very smoothly without any rendering issues and consumes low processing power.
Color gamut – The color gamut is the range of colors that a display can produce. A widely held and exploited misconception is that the bigger the color gamut the better – but it isn’t… If you want to see accurate colors in photos, videos, and all standard consumer content the display needs to match the Standard color gamut that was used to produce the content, which is called sRGB / Rec.709. A display with a larger color gamut cannot show colors that are not in the original content – it just exaggerates and distorts the colors. A smaller color gamut produces subdued colors, and too large a color gamut produces over saturated and even gaudy colors. That’s why a smaller color gamut is visually better than too large a color gamut. Most LCDs have a color gamut smaller than the Standard and most OLEDs have a color gamut larger than the standard.
NTSC Color gamut – You’ll see the NTSC color gamut spec listed for some displays and reviews. It’s an indication that the manufacturer or reviewer is way out of touch. The NTSC Color gamut was defined about 60 years ago in 1953 and has been obsolete for over 30 years. It was never actually a true color gamut standard because consumer TVs never produced the NTSC Gamut even way back then. Specifying the ancient NTSC instead of the current sRGB / Rec.709 Color Gamut Spec is ridiculous…
16 Million Colors – You’ll see this Spec for most HDTVs, Tablets, Smartphones, Laptops and Monitors. 16Million Colors is effectively the standard for most consumer content (including digital cameras). But it doesn’t mean what most people think it does – a larger number of colors does NOT mean a larger color gamut – it is merely the total number of possible combinations of the red, green and blue primary color intensities. The primaries each have 256 possible intensity levels – that produces 256x256x256 = 16.7Million possible intensity combinations, which are not really colors in the intuitive sense. For 16 million colors, each primary color needs 256 intensity levels, which is 8-bits in binary. Since there are 3 primary colors and each has 8-bits, they add up to 24-bits. That’s called 24-bit color and you’ll sometimes see this Spec listed instead of 16 million colors.
Contrast Ratio – Contrast ratio is the spec that tells you how good the display is at reproducing relatively dark content, particularly at or near black. It is the ratio of whitest white to blackest black that a display can produce. It is measured in an absolutely pitch black Lab. It is very important if you watch movies with dark content under low ambient lighting. It’s not so important if you are watching in bright ambient lighting (like for many HDTVs and most mobile devices) or when watching ordinary television shows and sporting events (because they have almost no dark content). Mobile displays should have at least a true contrast ratio of 500 and home theater HDTVs at least 1,500 (a good LCD).
170+ Degree viewing angles – Many HDTVs, tablets, smartphones, laptops and monitors list a viewing angle spec, which is the full angle (compared to 180 degrees) within which the display can supposedly be watched with satisfactory picture quality. 170 degrees is 85 degrees out of a possible 90 degrees. The spec seems to imply that unless you are watching from a ridiculous 5 degrees from the edge of the screen you will see a perfectly fine image on the screen. This spec is nonsense and very misleading because it is defined for the angle where the contrast ratio falls to an abysmal 10. That is generally less than 1-percent of the contrast ratio seen when viewing the screen face on – so the picture quality will also be abysmal at that viewing angle. Viewing from other than the face-on center sweet spot generally decreases image and picture quality for effectively all displays. For example, in high-end IPS LCDs the brightness and contrast ratio both fall by roughly 50 percent at 30 degrees. For other LCDs there are also noticeable color shifts at 15 degrees as shown in this article. For OLED displays we measured a 30 percent brightness decrease and noticeable color shifts at 30 degrees. So, the standard viewing angle spec is useless. The best way to evaluate it yourself is to look at a fixed moderately colorful image or photo and see how the image changes as you shift your viewing position.
LED TVs and Displays – There is actually no true LED TV. The LED TVs that we are seeing today are actually LCD panels backlit by an array of LEDs. In earlier days, these panels were backlit by Cold Cathode Fluorescent Lights (CCFLs). In any true LED TV there should be an array of Light Emitting Diodes wherein each individual LED must be illuminating single pixel on the screen. But in actual world today this is not the case.
Brightness – In general, the display with higher brightness level is considered as better. But people often set the screen brightness too high, which causes eye strain and wastes power (and reduces battery running time). The optimum screen brightness varies with the current level of ambient lighting. Many displays have automatic brightness controls that should appropriately adjust the screen Brightness. High screen brightness is only useful when you need to look at the screen under high ambient lighting. But under these circumstances the reflectance of the screen is actually more important than the screen Brightness because it washes out the image, and you generally see reflections of your face and the area behind you, which is distracting and causes eye strain from involuntarily focusing on them instead of the screen content.
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