What is ISO 15781- Measuring shooting time lag, shutter release time lag, shooting rate, and start-up time lag about?  
ISO 15781 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.
ISO 15781 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.
Note: ISO 15781 does not address the measurement either of autofocus speed below recommended illumination level or autofocus accuracy.  
Who is ISO 15781- Measuring shooting time lag, shutter release time lag, shooting rate, and start-up time lag for? 
 ISO 15781 on measuring shooting time lag, shutter release time lag, shooting rate, and start-up time lag is useful for:  
- Digital photographer
- Manufacturers of digital camera
- Photo quality assessors
- Photograph production personnel
Why should you use ISO 15781- Measuring shooting time lag, shutter release time lag, shooting rate, and start-up time lag?  
 Taking pictures of a moving target was nearly impossible in the early days of digital photography. After pressing the exposure button, it took a significant amount of time to capture the image and the chance to preserve the desired moment was gone.
Part of the time between pressing the exposure button and the exposed picture is needed to focus, another part is needed to adjust the exposure, etc. This unwelcome but unavoidable period of time is called shooting time lag. This is often mixed with the term shutter release time lag, which is also defined in ISO 15781. Optimized systems are nowadays able to decrease these time lags.
Capturing the different stages of a fast-moving object is sometimes very important, especially in areas like sports or people photography. This high shooting rate requires fast image processing within the digital still camera that can be measured according to the method described in ISO 15781.
When a photographer decides to capture an image of a changing scene, if his or her digital still camera takes a long time to be ready to shoot once it is turned on, the opportunity to capture the image is lost. This time named start-up time lag is, therefore, another important value, which can be determined using ISO 15781. 
What’s changed since the last update?
ISO 15781:2019 supersedes BS ISO 15781:2015, which is withdrawn. The main change compared to the previous edition is the current scope includes digital still cameras that continuously shoot images into the buffer and select an image depending on the moment the exposure button is pressed. 
