PDAF, lasers and more: how does autofocus work on a cell phone camera?

Understanding which autofocus systems are best based on the type of scene and ambient lighting; we have collected advantages and limitations of the main methods

PDF extension it is the most popular autofocus system in cell phone cameras. However, smartphones can also use other systems and technologies, such as laser autofocus (LAF) and Dual Pixel cameras, to achieve greater focusing speed and accuracy in scenes.

Auto focus helps ensure that your phone camera photos are sharper and clearer. It can track moving objects, work in low-light situations, and use various scene recognition techniques to adjust focus faster than a manual focus lens.

What is Phase Detection Auto Focus (PDAF)?

OR phase detection auto focus (PDAF) uses photodiodes scattered around the image sensor to detect if an object is “in phase”, i.e. in focus.

A sensor with PDAF measures the angles of the light rays hitting the pair of photodiodes to calculate the distance between the camera and the object being photographed. When light rays from an object are perfectly aligned across the pair of photodiodes, that object is in focus.

What are the benefits of PDAF?

• PDAF is faster than CDAF: PDAF instantly detects the alignment of light rays to determine focus on an object, while CDAF has to look for regions of contrast in various focus options, which slows it down;
• More efficient in low light conditions: Because PDAF works by sensing the phase of light, it may perform better than CDAF in low-light situations, when image contrast tends to be very low.

What are the limitations of PDAF?

• Smaller precision area: PDAF, especially on DSLR cameras and simpler cell phones, uses only a subset of pixels to detect focus, which can limit accuracy in areas without focal point coverage, such as the corners of the image;
• Possible loss of image definition: When a group of pixels is replaced by phase detectors, the color information of these pixels is lost, which can degrade the image quality even with interpolation techniques.

What is Dual Pixel Autofocus?

Double pixel it is an improvement over PDAF which uses all pixels on the image sensor for phase detection. In this technology, each pixel has two vertically divided photodiodes (one on the left and one on the right), which improves autofocus accuracy and coverage.

What is the difference between Dual Pixel and Dual Pixel Pro?

OR Double Pixel Pro it has green pixels with diagonally split photodiodes instead of the vertical split of the Dual Pixel. With this, phase detection is performed not only on the left and right sides but also on the top and bottom. The technology was launched on the Samsung Isocell GN2 sensor and, according to the manufacturer, is faster and more accurate.

What is Contrast Detection Auto Focus (CDAF)?

OR Contrast Detection Auto Focus (CDAF) measures the difference between the lightest and darkest points in the image to identify if the image is in focus. That is, the technology is based on the principle that the higher the contrast, the better the sharpness of the image.

Unlike PDAF, which instantly measures the distance to an object using phase detection, CDAF works by testing different camera lens focus points and then selecting the position that produced the greatest contrast.

What is the advantage of the CDAF system?

• Cheaper to produce: The CDAF is an autofocus system that needs fewer components to operate, since it does not require photodiodes or lasers to measure distances, which reduces its cost;

What are the limits of the CDAF system?

• Focus slowdown: because CDAF needs to find the image with the highest contrast between the different focus points, it tends to give a slower focusing speed than other systems;
• Difficulty following moving objects: Due to the time it takes to find the ideal focus point, CDAF will have a harder time focusing when there are fast moving objects in the scene;
• Doesn’t work well in low light: CDAF may be slower or not focus when lighting is poor, as contrast suffers in these conditions.

What is Laser Auto Focus (LAF)?

OR laser auto focus (LAF) OR Laser Detect Auto Focus (LDAF) uses a small ToF (Time-of-Flight) sensor and a laser beam, usually infrared and invisible to the naked eye, to calculate the distance to an object.

In this system, a beam of light is emitted onto an object and reflected back to the ToF sensor. Since the speed of light is known, the distance to the object can be calculated by the time it takes for the light to return to the sensor. Finally, the lens adjusts to the detected distance, bringing the subject into focus.

What are the benefits of laser focus?

• Faster focus speed: LAF can detect distance and adjust focus almost instantly, as the speed of light is extremely high;
• It works even in low light conditions: the LAF emits its own laser to focus, therefore it does not depend on ambient lighting and can be effective even in low light conditions;

What are the limitations of laser focus?

• distance limit: since laser and sensor power is limited, LAF is only effective for objects closest to the camera, generally no more than 5 meters away;
• Higher production cost: LAF requires not only an additional laser in the mobile phone, but also a time-of-flight sensor, which can make production more expensive;
• May not be effective with certain items: If an object is too reflective or absorbs too much laser light, LAF will not be able to calculate the correct distance.

What is Hybrid Autofocus (HAF)?

OR Hybrid Auto Focus (HAF) it is a combination of several autofocus technologies in the same camera, such as PDAF, CDAF and LAF. It works by switching between different focusing methods to minimize each other’s weak points depending on environmental conditions.

More expensive phones often have more than one focus system, all of which combine to improve camera performance. On the Google Pixel 7, for example, the image processor uses PDAF to focus on moving scenes and automatically switches to LAF when it detects nearby objects.

PDAF, lasers and more: how does autofocus work on a cell phone camera?

Source: Terra

Rose

Rose James is a Gossipify movie and series reviewer known for her in-depth analysis and unique perspective on the latest releases. With a background in film studies, she provides engaging and informative reviews, and keeps readers up to date with industry trends and emerging talents.