Saturday, 22 February 2014

Increasing Mega Pixels Race in Mobile Industry-Myth

Lumia 1020 with 41 Mega Pixel Sensor

Since last 4-5 years everyone is familiar with the term "Mega Pixel". The general presumption among almost all the people is (>95%) that increased mega pixels means better camera, better photo quality. This is absolutely wrong. What defines the particular camera as "best" is out of context in this article. I am writing this to explain everything about the sensors and mega pixel racing in mobile industry. Let start with "Mega Pixel" definition

1 Mega Pixel= 1 million picture elements (Pixels) also called as photo sites. 

Which means that there will be so called 1 million pixels in a device of 1MP camera.

The immediate questions that should come in mind is, in "how much amount of area these pixels are spatially arranged ?"

For example assume the following condition

You have a rectangle with 6 boxes of similar size 

Now assume 1 box is equal to 1 mega pixel and the rectangle as sensor

Now you have 6 mp in a rectangular sensor

If you take the same size rectangle and put 12 boxes i.e 12 mega pixels, the box size will be half the size of original boxes.

If you compare the two rectangles side by side in below picture you can see 

Image A
Image B

The size of the rectangle remains same, what differs between both of them is the  "no of boxes" (i.e no of mega pixels).

If you calculate the size of individual box in the rectangle 

1 box individual size = X in image A and 2X in image B

The final conclusion from the above example is if the total area remains same, the size of individual boxes (i.e pixels) depends on their total number or vice-versa.

Now we will move on to camera sensors
Usually the camera sensors are measured in inch squares (Applicable to both Mobile Cameras and High End DSLR's) and individual pixel size varies between 1 to 3 micro meter (µm) usually depending on the sensor size.

Eg : 1/3.2", 1/2.3", 1/1.5", 1" etc

In the below chart you can check various sensor sizes available in industry

This image is not subject to scale

Smartphones usually employ a 1/3.2 inch sensors (>70% Mobiles). If one convert it to decimals, it roughly about 0.3125 inch square (That's pretty small !). What smartphone vendors actually doing is, they are just increasing the no.of pixels keeping the sensor size constant. Take the below examples of some smartphone camera sensors and individual pixel sizes.
1 individual pixel size= 1 box size anology in above example.

Will start with Apple and Samsung strategy

iPhone 4- 1/3.2" with individual pixel size 1.75 µm (5MP)
iPhone 4S- 1/3.2" with individual pixel size 1.4 µm (8MP)
iPhone 5- 1/3.2" with individual pixel size 1.4 µm (8MP)
iPhone 5S- 1/3" with individual pixel size of 1.5 µm (8MP)

If you carefully see the above list, iPhone camera sensors over the years the sensor size almost remained same. If you compare iPhone 4 which has 5MP sensor and iPhone 4S which has 8MP sensor yet maintaining the same size. Hence in iPhone 4S due to more pixels in same sensor size the individual pixel size decreased to 1.4µm from 1.75µm and if you compare iPhone 5 and 5S which has yet again 8MP sensor, but there is minute difference in sensor size (1/3.2 vs 1/3 inch), hence iPhone 5S has slightly increased individual pixel size.

Galaxy S2- 1/3.2" with individual pixel size of 1.4 µm (8MP)
Galaxy S3- ~1/3" with individual pixel size of 1.4 µm (8MP)
Galaxy S4- ~1/3.06" with individual pixel size of 1.12 µm (13MP)

If you take Samsung Galaxy S series flagships, they also followed the same principle.

Galaxy S2 and S3 has same sensor size and 8MP but when it comes to S4 the mega pixels are bumped up to 13MP which resulted in decreased "Individual Pixel Size" of 1.12µm from 1.4µm.

You may ask me now "Whats wrong with that ?". According to the laws of physics, more the number of pixels, more the noise and less quality (when both sensors are of same size). No one can deny this basic fact. It a pure marketing technique employed by such above mentioned companies for better reach to masses. The seller can easily convince customer that it has 13Mp compared to previous 8MP so on and also they get the advantage of slim phones. I am not complaining that there was no increase in photo quality of the above said smart phones. There is definitely substantial increase in their image quality over the years due to various other reasons like for example if you take all the camera sensors in S4 and iPhone 5s are Back Side Illuminated sensors (BSI) as opposed to previous generation front side illuminated sensors (FSI).
[In FSI's the pixels on sensor are connected to tiny wire on front side, so when the ray of light strikes the sensor (specifically  say Photons) there is chance that these tiny wires may obstruct the "efficiency". This problems is solved by placing the tiny wires  back side (BSI).]

Image quality also depends on other improtant factors like aperture value, more polished software algorithms which keep on changing from time to time, lens optics quality and their make, no of lens elements etc. For example Samsung extensively process the  captured image to JPG format by better algorithms, its more like an artificial reconstruction process in image editing. Apple over saturate the colors for better feel (Pseudo). All these methods merely software based enhancements that pleases the customer "temporarily".
Lets move on to Nokia and HTC who are trying to improve imaging standards genuinely !

I think everyone is aware of Nokia's 41MP phones ? After reading the above article you may sense that 41 MP is also a gimmick or marketing technique, its absolutely wrong ! First of all the 41MP sensor in 808 and Lumia 1020 are very much bigger than most point and shoot camera's.

In 808, Nokia used 1/1.2" FSI sensor with individual pixel size of 1.4µm,
In Lumia 1020, they used 1/1.5" BSI sensor with Individual pixel size of 1.12µm.
So both the sensors are almost double the normal sensors used in smartphones, check the previous above image for comparison. (The loss of image quality with decreased individual pixel size (Slightly smaller sensor) in 1020 is compensated by BSI sensor).

The sensor size just matters small portion of these two phones imaging technology. The whole concept behind using such large sensor is out of scope in this article. I will simply put the concept in two lines. These two camera phones over samples images of 41Mp size in to 5MP size photos which means that roughly data from 7 individual pixels in re framed to one big pixel using sophisticated algorithms. Such over sampling process is called as "Pixel Binning" and is commonly used in satellite imaging the earth.

During this re framing, most of the visual noise is reduced. There is one more added advantage with this oversampling process. In real time while taking pictures, this process enables us to have 2x-3x lossless digital zoom in still images and 4x-6x in video shooting mode depending on the video resolution taken.(Lossless digital zoom means there is no loss in image quality when zoomed as opposed to loss with original digital zoom)
Compare the two images crops from Lumia 1020 one is unaltered(Top) and other is over sampled (Middle) and bottom one is same image crop from 808.

Top is unaltered crop from normal image and middle is over sampled image from
the same (Both from 1020) and the last bottom one is over sampled image from 808
You can clearly see the difference of having such tech, the last two have less visual noise compared to top image crop (Forget color saturation between both phones). Nokia trading such tech using "Pureview" brand.
Image Credit : Steve Litchfield

Lets come to HTC
Inspired from Nokia, in 2012 HTC announced new smartphone "HTC One" with a tag "Ultrapixel" (Clever naming). I had seen many people thinking that Ultrapixel and Megapixel are different things, but they are not ! Ultrapixel is just a trade name or brand name for HTC phones with some improved imaging technology. What actually HTC did in their  "One" phone is, they bumped up the individual pixel size to 2µm than usual 1.4µm found in other smartphones, thus following the laws of physics straightly. 
The sensor specs are 1/3" BSI sensor with individual pixel size 2µm

Check out the beautiful illustration by HTC 

More the individual pixel size more the light to pass through, better the image quality
HTC thought to capitalize the  Android ecosystem since Nokia is completely absent here.
Obviously HTC failed to capitalize such tech, as I mentioned in first paragraph that everyone thinks that higher the MP, better the clarity, its very hard to convince normal users that actual 4Mp photos of HTC One are superior to other competitive smartphones with 8-12MP. To lesser extent, the hurried release of  "Ultrapixel" tech with poor imaging algorithms also attributed to its failure. 

In conclusion, the quality image is defined by several factors which I did not mention them here. The message to be taken from this article is, never think that higher the MP better the image quality. The image quality actually declines when both the sensors are of same size. The most important factor one should consider before buying a camera smartphone or even a camera is the size of sensor, next the optics system and their make and so on desired features. Don't bother about mega pixels anytime when you are buying a camera or smartphone (If mainly for camera purpose) you may get trapped in OEM's marketing gimmicks.

Note: The reason for selecting these four OEM's is, since they together make more than 80% of the mobile market, nothing more than that.

Comments and views are welcome :)

Note: Next article would be on "Scientific Approaches to weight loss or gain".


satyajith av said...

Oka muka ardham aithe Nag meda otu

itsyoursreekanth said...

good review. worth to read.