There’s a lot of people who think that more Megapixel can give them better image quality. Is this true? Apple’s cameras didn’t have that many megapixels but still great. Right?
According to DxOMark, newly launched Google Pixel 2 has the great camera. It got highest marks. But wait, Google Pixel 2 has only 12.2 Megapixel of the Single Rear camera. Then how it is the best camera device?
Let’s find out what you should know beyond the Megapixel.
What is Megapixel?
A megapixel (MP) is a million pixels; the term is used not only for the number of pixels in an image but also to express the number of image sensor elements of digital cameras or the number of display elements of digital displays. For example, a camera that makes a 2048×1536 pixel image (3,145,728 finished image pixels) typically uses a few extra rows and columns of sensor elements and is commonly said to have “3.2 megapixels” or “3.4 megapixels”, depending on whether the number reported is the “effective” or the “total” pixel count.
In the simplest terms, the megapixel rating is the total number of pixels that will make up and image captured by a camera sensor. To get the total number of pixels, you simply multiply the number of horizontal pixels by vertical pixels. For instance, a 3008 x 2000 sensor in my Pentax K100 DSLR equates to six megapixels.
Now there is much more to just the number of pixels that make up the sensor. You also have the size of the sensor. A smartphone and a DSLR. In general, a DSLR is able to take more accurate pictures because it uses lenses and sensors that are larger than the smartphone. Because the DSLR can absorb more light from the environment than the smartphone, it generally takes better pictures even if it has a lower overall megapixel count. This is important to remember because what I talk about from here on out is assumed that it is comparing two cameras with similar characteristics like lenses and sensor sizes but just different megapixel counts.
Not only Megapixel, there are more factors to judge a camera by their specifications.
1. Image Sensors:
According to Wikipedia, An image sensor or imaging sensor is a sensor that detects and conveys the information that constitutes an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, digital imaging tends to replace analog imaging.
Early analog sensors for visible light were video camera tubes. Currently, used types are semiconductor charge-coupled devices (CCD) or active pixel sensors in complementary metal–oxide–semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS, Live MOS) technologies. Analog sensors for invisible radiation tend to involve vacuum tubes of various kinds. Digital sensors include flat panel detectors.
Most digital cameras use a CMOS sensor, because CMOS sensors perform better than CCDs, offering faster speeds with lower power consumption. Most CMOS sensors incorporate an integrated circuit, helping reduce costs; CCD sensors are still in use for cheaper cameras but can demonstrate comparatively diminished performance (e.g. weakness in burst mode). Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.
Another design, a hybrid CCD/CMOS architecture (sold under the name “sCMOS”) consists of CMOS readout integrated circuits (ROICs) that are bump bonded to a CCD imaging substrate – a technology that was developed for infrared staring arrays and has been adapted to silicon-based detector technology. Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology: such structures can be achieved by separating individual poly-silicon gates by a very small gap; though still a product of research hybrid sensors can potentially harness the benefits of both CCD and CMOS imagers.
In Simple words, CMOS sensors are better than CCD sensors. A CMOS image sensor has an amplifier for each pixel compared to the few amplifiers of a CCD.
2. Pixel Size:
Sensor size is useful for getting an idea of how much space in the smartphone camera module is consumed by the sensor but less useful for gauging total light collection as megapixel counts vary between smartphones. This is where pixel size comes in, giving a direct measure of how large the individual photodetectors are in the CMOS sensor.
Pixel size for smartphones fits into a narrow range between one and two micrometers (or microns, abbreviated as µm) in either the horizontal or vertical direction. Again, the larger you go, the lighter each pixel can collect. This is why the HTC One M8’s camera, with a 2.0-micron pixel size, performs a lot better in dark conditions than the Samsung Galaxy S5, with 1.12-micron pixels. It’s simply because the pixels are larger and can capture more light.
The technology behind the design of the CMOS sensor can affect the light gathering properties of each individual pixel, but the easiest way to compare is just by going on size. A camera with 1.4-micron pixels captures twice the light (per pixel) of one with 1.0-micron pixels, calculated by comparing the difference in the total area. Another way of saying this is that the 1.4-micron sensor is one stop brighter.
Calculating these differences becomes very easy. The Apple iPhone 5s’ camera has a pixel size of 1.5 µm, which can capture approximately 88% more light per pixel than a 1.12 µm sensor found in the Sony Xperia Z2, for example. This is despite the Z2 having a larger sensor overall (1/2.3” versus 1/3.0”), as the Z2 has a much larger megapixel count (20.7 MP versus 8.0 MP).
There’s no correct answer to which one is better, as it comes down to what you’re after from your smartphone camera. You’ll typically get better low-light images with larger pixel sizes, but a higher megapixel count may be more appealing if you shoot mostly during daytime. As always, I’d recommend checking the camera specifications and sample images for any smartphone you’re considering purchasing, to see what sort of camera you’ll end up with.
3. Aperture and F-Number:
A much more important value is the size of the camera’s aperture, commonly listed as an f-number. The f-number is a ratio between the focal length and size of the hole, and tells you how much light can pass through to the sensor. An f-number of 2, expressed typically as f/2, means the focal length is twice the size of the aperture; f/4 would be a focal length 4 times the aperture, and so forth.
The lower the f-number, the wider the aperture and thus more light is able to pass through. Differences in f-number aren’t immediately obvious though, as double the f-number doesn’t equate to half the light gathering area (one stop less). Instead, due to the circular nature of an aperture, double the f-number is a two stop difference, providing one-quarter of the light gathering area.
Smartphone cameras typically use apertures ranging from f/2.0 to f/2.4, which are both wide in the overall camera ecosystem, but there are big differences between the two. f/2.4 is a half stop less than f/2.0, therefore a f/2.0 lens transmits 50% more light to the sensor. This can have a significant effect on low-light performance, with f/2.0-lensed smartphones typically producing stronger results than their f/2.4 counterparts.
The difference in f-number doesn’t just affect light gathering properties. A lens with a higher f-number has a wider depth of field, typically sharper images, less prevalent chromatic aberration (colored fringes in areas of a photo with high contrast) and weaker bokeh (pleasant blur as a result of defocused areas outside the depth of field range).
Here we find another trade-off. In some situations, shallower depth of field and strong bokeh is preferred – especially when shooting subjects up-close or in macro mode – as it places the focal point of the image squarely on the subject rather than the background. DSLRs are particularly good at producing pleasant bokeh with a good lens; on smartphones, the effect is less noticeable, but still present comparing f/2.0 and f/2.4 lenses.
While chromatic aberrations and sharpness are issues with wider apertures (at times the HTC One M8’s f/2.0 lens can produce images with noticeable chromatic aberrations), it always falls second place to low light sensitivity and depth-of-field. This is why, in nearly all circumstances, wider apertures are preferred over smaller apertures. Unfortunately, wide-aperture lenses are more complex and more expensive to produce, which is why not all smartphones manufacturers use them.
4. Image Processing:
In addition to the size and quality of the lens and sensor, there’s also the image processor. Most modern high-end smartphone CPUs have dedicated graphics processors built into the chip, which, being hardware-accelerated and not just software-dependent, can quickly render images like photos, videos, and games without overtaxing the main application processor.
HTC and Samsung have been pushing continuous-burst mode hard, averaging one shot in a tenth of a second or less, thanks to separate hardware-accelerated image processors that can capture shots like nobody’s business. However, since burst mode doesn’t give you time to focus, expect to see some blur.
I promised that there was software bridging the hardware and the final image, and there is. Algorithms and other logic are what create the final image output on the phone’s screen. This is where the most subjective element of photography comes in: how your eye interprets the quality of color, the photo’s sharpness, and so on.
The image processor is also what helps achieve zero shutter lag when the camera captures the photo when you press the capture button, not a beat or two after.
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