FIXME **This page is not fully translated, yet. Please help completing the translation.**\\ // (remove this paragraph once the translation is finished) // ==== Auto Exposure (AE) ==== Proper exposure makes images look more realistic and comfortable, and it is the first and crucial step affecting subsequent image processing. The three common parameters for controlling exposure are exposure time, sensitivity (ISO), and aperture. As one of the three common means to control exposure, aperture is rarely mentioned in mobile phones due to size constraints. However, in recent years, with the improvement of user awareness and technological progress, and also because aperture simultaneously affects the depth of field, an increasing number of flagship models have achieved variable aperture for the main camera. These three methods now coexist in mobile imaging systems to control exposure and depth of field.\\ {{ yanding:ae1.png?600 |}} **The aperture refers to the opening formed by overlapping small blades inside the lens.**\\ Let's first talk about EV (Exposure Value), which is determined by aperture and shutter speed. For the same CMOS sensor, the EV obtained at f/5.6 and 1/125s is equivalent to that at f/2 and 1/1000s, f/2.8 and 1/500s, f/4 and 1/250s, or f/8 and 1/60s. Despite the different characteristics, the resulting image brightness is the same. Its calculation formula is as follows:\\ {{ yanding:ae2.png?400 |}} The larger the aperture, the more light enters the lens; the smaller the aperture, the less light enters. Therefore, the size of the aperture directly affects the amount of light entering the camera, thereby influencing the camera's exposure.\\ {{ yanding:ae3.png?500 |}} The job of AE (Auto Exposure) is to provide correct exposure and meet these requirements, reducing the need to manually set device parameters when capturing photos or videos. In some fields, such as automotive applications, exposure can only rely on AE. When manually controlling exposure without AE, the "sunny f/16 rule" we often hear refers to the fact that under bright sunlight, with the aperture set to f/16 and the shutter speed equal to the reciprocal of the ISO sensitivity, a relatively correct exposure can be achieved without an extra light meter or the camera's internal metering. Taking ISO 200 as an example, when the aperture is f/16, the shutter speed must be 1/250s for correct exposure. However, not every shutter speed setting can precisely match the ISO value, so a value close to the ISO must be chosen:\\ Sunny f/16\\ ISO 100 ⇒ 1/125s\\ ISO 200 ⇒ 1/250s\\ ISO 400 ⇒ 1/500s\\ ISO 800 ⇒ 1/1000s\\ ISO 1600 ⇒ 1/2000s\\ **Aperture Adjustment**\\ In actual shooting, it is impossible to always use an f/16 aperture. To maintain correct exposure, we need a certain amount of exposure. Across different aperture settings, the choice of aperture and shutter speed must still follow this rule. The amount of light reaching the sensor depends on the shutter speed and aperture.\\ In video recording, the requirements for variable aperture are more meticulous. To obtain stable frames, avoid "stuttering" caused by excessively short exposure times, and simultaneously achieve stable noise performance, a fixed exposure time and ISO are usually adopted, using only the aperture to control exposure. This allows the footage to have stable "motion blur," making it look smoother and more natural.\\ {{ yanding:ae4.png?600 |}} For example, if the aperture changes from f/5.6 to f/4 while the shutter speed remains unchanged, twice the amount of light will reach the image sensor. However, more light will lead to overexposure. To avoid overexposure, the shutter speed or ISO must be halved.\\ **Same ISO Sensitivity**\\ | ISO 200 | f/16 | 1/250s | | ISO 200 | f/11 | 1/500s | | ISO 200 | f/8 | 1/1000s | | ISO 200 | f/5.6 | 1/2000s | If we want to increase the aperture without changing the shutter speed, we can decrease the ISO sensitivity to keep the amount of light constant. Increasing the aperture by one f-stop is equivalent to halving the sensitivity. Under very good lighting conditions and with a very fast shutter speed, it is possible to reach the camera's limits. If neither ISO nor shutter speed can sufficiently reduce the amount of light, the use of a neutral density (ND) filter is recommended.\\ **Same Shutter Speed**\\ | 1/4000s | f/8 | ISO 800 | | 1/4000s | f/5.6 | ISO 400 | | 1/4000s | f/4 | ISO 200 | | 1/4000s | f/2.8 | ISO 100 | **Sunny to Cloudy**\\ The "sunny f/16 rule" refers to clear weather conditions. However, this rule can even be applied when the sky becomes overcast or night falls. Applying different aperture settings mainly depends on the lighting conditions and shadow details.\\ | Snow or sand in sunlight, shadows with sharp edges | f/22 | ISO 100 | 1/125s | | Bright sunlight, distinct shadows | f/16 | ISO 100 | 1/125s | | Slightly overcast, shadows with soft edges | f/11 | ISO 100 | 1/125s | | Overcast, barely visible shadows | f/8 | ISO 100 | 1/125s | | Heavy overcast, no shadows | f/5.6 | ISO 100 | 1/125s | | Sunset, no shadows | f/4 | ISO 100 | 1/125s | Based on the above, we can calculate the roughly correct exposure parameters corresponding to the ambient light. However, on mobile phones, many other factors affect parameter settings. For example, a smaller aperture is needed when we want to maximize the depth of field; the shortest possible exposure time is required to meet algorithmic synthesis or reduce motion blur; and a lower ISO is needed to achieve a better signal-to-noise ratio.\\ These requirements necessitate a testing device that can accurately control brightness and simultaneously conduct comparative tests on shutter speeds to obtain the optimal exposure parameters.\\ The MLB-LTM light box is a dual-sided comparable light box that covers various tests, including motion blur.\\ {{ yanding:mlb-ltm.png?600 |}} Many image quality factors can be best tested using test charts, but some tests (such as exposure and motion blur-related tests) can be better evaluated using real-world scenes. The real-scene test light box contains real-scene test objects with various colors and texture details for accurate subjective visual analysis and comparison, allowing subjective evaluation of image quality through internal scene comparison. Building on the static real-scene light box, two transmissive light boxes have been added, which can be paired with transmissive test charts to create and test high-contrast scenes and HDR high dynamic range tests. A moving track function has been added, along with a left-right moving portrait chart and a 360-degree rotating turntable, which are highly useful for testing motion artifacts and evaluating blur in both photography and video. Comprising a top light source, two HDR transmissive light boxes, and moving targets, the light box accommodates multiple testing possibilities, enriching testing methods and improving testing efficiency.\\