Camera---(8) Mobile phone camera basic knowledge analysis _camera

Today, photography has become one of the most important functions of mobile phones, and is also the first factor in the cost of acquiring mobile phones. And to some extent, mobile phones have now replaced professional cameras and become the most important photography in our everyday life. Therefore, in the base hardware play to a fever in the future, mobile phone manufacturers are beginning to focus on our attention to the photographic function.

"XXX pixel", "XXX sensor", "XXX Lens", "xxx aperture", when faced with these arrogant and noisy camera selling point, as not familiar with the general cost of the camera, many people become dazed, beginning will only do the addition and subtraction algorithm, as the highest is the best, and for these parameters represent the real meaning, But don't know.

Pixel ≠ clarity

　　

The composition of mobile phone camera

　　

First of all, let's take a look at the makeup of mobile phone cameras. The need to pay attention is that, although we call it "mobile phone camera" or "mobile phone camera", but internship, its components and operating principles and traditional digital cameras, only small size, so "mobile phone digital Camera" is the title is intact, standard.

(Figure II)

Pixel

　　

"Pixel" as we know the most of the camera parameters, in the understanding of a mobile phone camera, the first to see should be "XXX million pixels", the majority of manufacturers will also be the first to promote the point, then this pixel ultimately means what.

"Pixel" refers to the smallest photosensitive unit on the camera sensor, and we generally say "XXX million pixel" practice refers to the camera resolution, its numerical size is primarily by the camera sensor pixel (that is, the smallest photosensitive unit) number of choices, such as 5 million pixels means that the sensor has 5 million pixels, and the number of pixels in the screen of the cell phone screen is 720p or 1080p resolution is a truth.

(Figure III)

Pixel Choice photo quality.

　　

We generally think that the higher the camera pixel, the more clear the photo taken, the internship on this is very one-sided. The pixel of a camera can only choose the resolution of its pictures, and the higher the resolution of the picture, the larger the scale of the picture, and the clearer the picture is.

　　

Excluding other elements, the 13 million-megapixel camera and the 8 million-megapixel camera picture, on the computer screen presented on the scale is not the same, and the clarity is almost no difference.

　　

Not the same thing, when the picture is checked on the phone, the screen will typically scale two pictures to the same scale, and now the 13 million megapixel camera will have a higher pixel density (the number of pixels per inch of the screen), in theory, a higher degree of clarity, more detailed picture details.

　　

But at that time the mainstream mobile phone screen for the 1080p level (1920x1080 pixels), whether it is the 13 million megapixel camera 4208x3120 pixel photos, is still a 8 million-megapixel camera 3200x2400 pixel photos, are beyond the 1080p screen reading scale, Will eventually be 1920x1080 pixel flashes, so the visibility of the naked eye is also no difference.

　

So where is the advantage of high pixel?

　　

As the previous article says, higher-pixel cameras take pictures on a larger scale, assuming we want to print out the proofs, using the usual 300-pixel/inch print specification to account for the 13 million-megapixel camera's 4208x3120 pixel proofs, which can print 17-inch photographs, while the 8 million-megapixel camera's 3200x 2400 pixel proofs, printing a picture beyond 13 inches is beginning to be ambiguous. It is significant that the 13 million megapixel camera proofs can be printed on a larger scale.

　　

Ultimately, Pixels can't choose the quality of the photos, and perhaps the pixel is not the only factor in choosing the quality of the photo. In the computer, mobile phone screen, such as the main inspection channels, the 13 million-pixel camera, 8 million pixel or higher 16 million pixels, 20.7 million pixels to take photos of the clarity of the show is no difference.

　　

So, if your demand for mobile phone photography is limited to common records and sharing, then the market with 8 million-megapixel, 13 million-megapixel camera of the mainstream thousand-cell phone, you can completely satisfied with your photo clarity of supplication, rather than follow the bandwagon to seek a higher number of pixels.

　　

But if you have a special demand for pictures, such as stamping or later cutting the drawing, then I will introduce you to the Lumia 1020 mobile phone.

(Figure IV)

Lumia 1020 Lens Close-up

Lumia 1020 is now the highest standard camera mobile phone, its sensors have 41 million pixel imaging talent, cut into our more square drawings, in 4:3 frames can produce a maximum of 38 million pixels of photos, and 16:9 frames can produce 34 million pixel photos.

In the meantime, the 38 million-pixel picture, at a 72-pixel/inch resolution, is the sum of the size of the image scale up to 70 15-inch flashes, which is assuming you think you're OK, and you can print it as a giant poster, which makes Lumia 1020 in the details of the force on the general mobile phone has a near-crush advantage.

The sensor is the most crucial

　　

Pixel is not the key element to choose the quality of the picture, then who is it? The answer is the sensor.

　　

We know that in the digital camera has not yet blown up, the traditional camera is used as the carrier of information, and the digital camera sensor is equivalent to "film." Sensors are the most important components of a camera, some of the most crucial skills.

　　

Camera sensors are primarily divided into two types, CCD and CMOS. CCD sensor, although the imaging quality is good, but the cost is high, and not suitable for mobile phones, and CMOS sensors by virtue of lower power consumption and price and excellent impression quality, in the mobile phone category most widely used.

CMOS sensor is divided into two types of back-and warehouse-type, both of which were developed by Sony, the Sony backlight sensor brand name "Exmor R", Warehouse-type sensor for "Exmor RS".

　　

Relatively speaking, the larger the sensor scale, the better the photographic function, the more the captured photon (graphic signal), the lower the signal-to-noise ratio, the more natural imaging effect, but the larger sensor will cause the volume of mobile phones, components, cost added.

(Figure V)

The appearance of the backlight sensor, useful to deal with this question, at the same scale, it makes the sensor photosensitive ability to progress 100%, useful to improve the image quality in the weak light environment. Therefore, before buying a camera phone, users will be the first to consider whether the camera is using the Exmor R back-camera sensor.

(Figure VI)

August 2012, Sony released a new warehouse-type sensor (Exmor RS CMOS), the need to pay attention to is that it and the backlight sensor is not the evolution of contact, but the side of the link, the first advantage of the warehouse-type sensor in the case of the number of pixels adhere to the same situation, so that the sensor scale becomes smaller, can also be understood as, The size of the warehouse-type sensor is smaller than the number of pixels in the back-camera sensor, which saves space and makes the phone thinner and lighter.

(Figure Seven)

In contrast, the advantage of a back-camera sensor in the warehouse-type sensor with the number of pixels together, although the sensor scale is larger, but a single pixel area (a single photosensitive area) will be larger, and then make the photosensitive function progress, natural dark light photographic effect is very good, the overall imaging effect is more excellent.

　　

Therefore, the two have characteristics, each have good and bad, can not be a simple or bad points, the key to see the manufacturers in the sensor scale and photosensitive talent how to choose.

　　

From the sensor, the author of our referral to the mobile phone is Sony's latest flagship model--xperia Z2, as the saying goes Tun, the machine monopoly of the first Sony into the 1/2.3-inch large Exmor RS Warehouse sensor (now the largest warehouse-type sensor), like a prime number of up to 20.7 million, and equipped with Sony SLR camera Special G lens.

Its advantage is longer than capturing the scene of light, full use of the robust camera lens to shoot a high resolution of the picture, and have higher sensitivity, reduce noise, to ensure that the picture lubrication clear, to a higher degree of fidelity to reproduce the photographic details.

(Fig. Eight) Lens: the more the more

Lens is the photographic scene in the sensor imaging equipment, the equivalent of the camera's "eyes", generally by a number of lenses, light signal through the period, the lenses will layer layer filter miscellaneous light (infra-red), so, the more lens film, imaging the more real.

From the raw material, the lens can be divided into plastic lenses (Plastic) and glass lenses (Glass), glass lens transmittance and imaging quality to be very good, but also higher cost, so the mobile phone lens is composed of plastic lenses.

If the lens is made up of 5 layers of plastic lenses, we call it 5P (Plastic) lens, and assuming that the lens consists of 4 layers of plastic lenses + 1-layer glass lenses, we should call them 4p1g lenses. However, because the job lacks a consistent cognitive standard, the 5P lens is generally understood as a lens composed of 5 layers of lenses, that is, the 4p1g lens will also be called the 5P lens.

Most mobile phones in the market today use 5P or 6P lenses, for example, the Millet 3 selected 5P lenses (4-layer plastic lenses + 1-layer blue glass lenses), while small cola selected a more high-end 6P lens (5 layers of plastic lenses + 1 layers of blue glass lenses), theoretically speaking, small cola lens imaging more real.

(Figure Nine)

Aperture: Still big good

In addition to filtering the clutter, the lens also chose a very important camera parameter, aperture.

　　

The aperture is composed of a few thin pieces of metal in the lens, which can be manipulated into the lens to reach the sensor's light by altering the aperture size. Aperture of the value of general use f/2.2, f/2.4 to indicate that the smaller the number, the greater the aperture, the two are inversely related to the case.

(Figure 10)
Aperture Demo Chart

Its operating principle is that the larger the aperture, the more the light that reaches the sensor through the lens, the brighter the image, the darker the picture. As a result, the imaging advantages of large aperture are more significant in night-shot or dark-light environments.

In addition to manipulating the light flux, the aperture also has the function of manipulating depth of the scene. In the days, we often see the scene of the virtual effect of the very strong photos, not only highlighted the focus of photography, but also has a very beautiful artistic sense, which is called depth of life. The larger the aperture, the smaller the depth of the scene, the more remarkable the effect of the set.

Therefore, when we choose to buy a camera phone, we should first choose a larger aperture of the product.

Nowadays, most of the mobile phones in the shopping malls are f2.4, f/2.2 or f2.0, while the iris of Lenovo Vibe Z arrives at f1.8, the largest cell phone of the aperture today.

(Figure 11)
Lenovo Vibe Z has both front and rear cameras, its front camera for 5 million pixels, and then the camera reached 13 million pixels (with dual LED flash), and selected IMX135 Sony New Generation warehouse sensor, with F1.8 large aperture, contrast F2.2 aperture lens into the light volume added 49%, Can bring the user very good weak light imaging embodiment.

The ISP chip is the brain.

Before we say ISP (Image Signal processing Chinese as "graphic signal processing"), let's take a look at the camera process of the mobile phone. After pressing the shutter, the light enters from the lens, arrives the sensor, the sensor acts as collects, records the light, and converts it to the electric current signal, then passes to the ISP graphics signal processor (hereinafter referred to as the ISP chip) carries on the processing, after all, the handset processor processing storage.

Therefore, the ISP chip is the photographic process of the operation of the Unit, its position is equivalent to the "brain" of the camera.

The effect of ISP chip is to carry on the operation processing to the signal that the sensor input, after all obtains through the linear correction, the noise point removal, the bad spot patching, the color interpolation, the white balance proofing, the exposure proofreading and so on processing result. ISP chip can choose to a large extent mobile phone camera imaging quality, generally it to the picture quality improvement space can reach 10%-15%.

ISP chip is divided into two kinds of integration and independent, independent ISP chip processing talent is superior to integrated ISP chip, but the cost is higher.

One, integrated ISP chip

At that time, most of the mobile phone using the processor conveniently integrated ISP chip, which is the ISP chip integrated in the phone's processor. Now the Gaotong Dragon series, the NVIDIA Tegra series of processors are integrated with ISP chip. Sony Xperia Z2, OPPOFind5, for example, is an integrated ISP chip using a High-pass processor.

(Figure 12)

Gaotong long processor with integrated ISP chip

The advantages of the processor-compatible integrated ISP chip are the reduction of handset development and production costs, but the disadvantages are:

1, excellent processor manufacturers and have to develop ISP chip, its imaging quality is inferior to independent ISP chip;

2, can not ensure that with the selection of sensors, both assume that the collaboration is not good, the image quality is negative effect, which constrains the mobile phone to the selection of sensors;

3, at that time the same price segment of the mobile phone most of the same processor, the same processor means the same ISP program, which leads to a grim homogeneity of the scene.

　

But there is also a special case, that is the iphone, it is well known that the iphone is carrying its own Apple processor, so, despite the iphone's choice of integrated ISP chip, but the above flaws are not there.

　　

Second, independent ISP chip

Independent ISP chips are independent of the processor, although the cost is high, but the advantages are also notable. In addition to computational talent, better imaging quality, the general independent ISP chip is the mobile phone provider to the ISP agreed to, so with the other components of the camera is better, imaging is attributed to its own characteristics, characteristics.

Today, Fujitsu is the premier independent ISP chip supplier, Samsung Galaxy S4 is the choice of Fujitsu's independent ISP chip.