Photometry of mobile phone photography

Before understanding the concept and skills of photometry, we must first understand the imaging process. The imaging process of mobile phone lens is the same as that of human eye. What we can see is not the object itself, but because it can reflect light. The light reflected by objects enters the eyes and then gathers on the retina behind the eyes to form images of these objects.

In order to form an image, the camera must first receive light, and then form an image on the digital photosensitive element (equivalent to the human retina). How much light is suitable for imaging? At this time, the concept of "exposure" was used. In the process of photography, the amount of light allowed to enter the lens and shine on the image sensor of a digital camera is called exposure. "Exposure" can be controlled by the combination of aperture, shutter and sensitivity of photosensitive medium.

If the photographed scene is too bright, the bright part can't see the details clearly without layers, which is overexposure; On the other hand, if the photo is very dark and cannot truly reflect the color of the object, it is called underexposure.

Let's start with "normal exposure". Under the same light source, we see that different objects are bright (such as white objects) and dark (such as gray objects). This is because the reflectivity of different objects is different. If the objects are normally represented by electronic photosensitive devices, the exposure of bright and dark parts is inconsistent. The exposure time of bright objects can be shorter because of their high reflectivity. However, there is only one exposure parameter of the camera, which cannot take into account all parts of the picture. Therefore, in the same viewing range, as long as the reflectivity of the object is different, there must be underexposure or overexposure. At this time, it depends on whether the photographer wants to shoot the bright part or the dark part. As long as the object he wants to show is normal exposure, the photo can be said to be "normal exposure".

Second, metering and exposure

If you want the subject to be exposed normally, measure the subject. At this point, you will understand that the purpose of measuring the subject is normal exposure. Click on the part of the mobile phone that you want to expose normally with your finger for metering, and all the places you point to will be exposed normally. The picture on the left below is to click on the dish on the plate for metering, and the picture on the right is to click on the plate for metering.

As shown in the left picture above, due to the large contrast between the light and shade of the dish and the dish, when measuring the dish on the dish, the mobile phone will ensure that the exposure of the dish is accurate and the picture taken is clear, because the exposure time is long, and the dish will be overexposed at this time, as shown in the left picture.

The picture on the right shows the photometry of the tableware tray. In order to ensure the correct exposure of the plate, the exposure time is short and the color of the dish is dark, so it is impossible to clearly display the color of the dish.

Third, exposure compensation

Another situation is that even if the metering point is placed on the subject, it is still not bright enough to see the details clearly. At this time, exposure compensation can be carried out, as shown below, the subject will become brighter and brighter by sliding up along the small sun.

Fourth, silhouette.

Overexposure or underexposure is not necessarily a bad thing. Sometimes we will use the characteristics of underexposure to form a silhouette (showing the outline of things) effect, as shown below.

Fifth, HDR mode.

So what should I do to make the dishes and plates exposed normally? An easier way is to use HDR mode. For example, if we turn on the HDR function of Apple's mobile phone, the iPhone will receive three Chinese photos of continuous shooting, and the exposure of these three photos is different, namely underexposed, normal exposed and overexposed. HDR will combine the best parts of three photos with different exposures to form an HDR photo. As shown below, click on the frame in the red circle to open HDR.

As mentioned above, the exposure is controlled by the aperture (the aperture size of the mobile phone is fixed), the shutter speed and the sensitivity of the photosensitive medium (reflected by iso value). In the next article, we will talk about shooting clear and sharp night scenes by adjusting shutter speed and iso value, as well as auxiliary equipment such as mobile phone tripod.