Detail of GB/T 42887-2023

Introduction of GB/T 42887-2023

GB/T 42887-2023 Digital still cameras - Measuring shooting time lag, shutter release time lag,shooting rate,and start-up time 1 Scope This document specifies how to measure and report the shooting time lag, shutter release time lag, shooting rate and start-up time lag for digital still cameras, including camera modules in phones and tablet computers. It includes a method that uses control signals inside the digital still camera and a method that determines the timing values without requiring access to the inside of the digital still camera. This document is applicable to the measurement of shooting delay, shutter delay, shooting speed and startup time of shooting modules of digital cameras, mobile phones and tablets. This document does not address the measurement either of auto focus speed below recommended illumination level or auto focus accuracy. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7589, Photography - Illuminants for sensitometry - Specifications for daylight, incandescent tungsten and printer 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 digital still camera device which incorporates an image sensor and produces a digital signal representing a still picture Note: A digital still camera is typically a portable, hand-held device. The digital signal is usually recorded on a removable memory, such as a solid-state memory card or magnetic disk. 3.2 shooting time lag tSL time elapsed from stand-by state to reaching capture point on a digital still camera or a module built into a mobile device and the beginning of the exposure Note 1: This period of time includes all measurements and adjustments (e.g. auto focus and exposure control) a digital still camera needs to make prior to the beginning of the exposure. Note 2: When the exposure button of a digital still camera is pressed it performs a number of time-consuming measurements and adjustments, e.g. determination of the exposure and focus adjustment. The time needed for these procedures is part of the shooting time lag. Note 3: A capture point is often initiated from stand-by state by firmly depressing the shutter button tothe maximum extent without introducing a discontinuity, see 3.8. 3.3 shutter release time lag tRL time elapsed from pre-capture point (3.7) to the time of starting the exposure by reaching capturepoint after having stabilized the focus operation (often due to half pressing of the shutter button), inthe case of digital still cameras that distinguish between pre-capture and capture points (3,8) (often thehalf pressing and the fully pressing of the shutter button) Note 1: Instead of shutter release time lag, the terms shutter lag and release lag are used in somepublications. Note 2: A capture point is often initiated from pre-capture point by fully pressing down the shutter button. 3.4 start-up time lag; tstart-up time elapsed between switching a digital still camera on and the moment the camera has reached astandby state (3.6) ready to shoot Note 1: Start-up time lag excludes the initialization of a memory card. Note 2: How this time is determined for the different devices is described in 5.2.1 3.5 shooting rate; fshooting reciprocal of the time elapsed between the beginning ofthe exposure of an image until the beginning ofthe exposure of the next image, that is, between successive capture start states 3.6 standby state state achieved following the power-up process, in which a digital still camera is powered on and readyto capture an image Note 1: lf the digital still camera uses an electronic viewfinder, a preview image is normally displayedduring the standby state. Note 2: Standby state excludes the initialization of a memory card. 3.7 pre-capture point position of a user control of a digital still camera which activates pre-capture processes, such as auto.focus and exposure calculation Note: The pre-capture point is typically reached by pressing an exposure button roughly halfwaydown on traditional digital still camera. On mobile devices with touchscreen this point might be reached by longpressing the trigger button. 3.8 capture point position of a user control of a digital still camera which activates the image capture operation Note: The capture point is typically reached by fully depressing the exposure button on traditionaldigital still cameras, On mobile devices with touchscreen this point can be reached either when pushing thetrigger button,or releasing it. 3.9 push duration total elapsed time during which the trigger button is pushed Note: This duration is not usually associated with a particular function on traditional digital still camera other than capture burst. On mobile devices that use a touchscreen, it can trigger some particular functions such as the autofocus. 4 Test conditions 4.1 Illumination of the test scene An illumination level between 500 lx to 5000 lx is recommended. Special measurement purposes may require other levels. The test scene shall be illuminated in a way that avoids specular reflection (see Figure 1). This can be achieved by using a geometry typical for reproduction photography, which means positioning the light sources in approximately a 45° angle to the surface of the chart. The illumination level of the area shall be reported together with the measurements. Timing measurements shall be performed under daylight conditions or a tungsten lamp. Procedures for determining whether the illumination used is an acceptable match to the daylight illuminant, shall be conducted in accordance with ISO 7589. 4.2 The chart and positioning of the digital still camera The digital still camera shall be mounted on a solid stand (e.g. heavy tripod) perpendicular to and facing the surface of the chart (see Figure 2). As for a test chart, the chart shall allow the digital still camera to focus easily and allow an easy determination whether the captured image is correctly focused. Examples include a black-and-white checker board or the three-line chart shown in informative Annex B. If the above condition is met, a typical image assessment chart may be used. Also, the ISO 12233 resolution chart may be placed in the chart area to determine whether the captured images are in focus. The height of the chart shall be (80 ±10) cm and the distance to the chart shall be adjusted in a way that the height of the image is in accord with the chart height. The surround areas should be filled with a reflective area of 18 % neutral grey. Prior to the measurement, the digital still camera shall be checked to see if it correctly focuses on the chart. If not, the correct focus shall be obtained by changing the chart or the illumination condition. If different setup conditions are required when the focal length of the lens is extremely long or short, these setup conditions shall be reported together with the measurement results.

Contents of GB/T 42887-2023