Determination of preliminary prayer time is a fundamental thing because praying must be done in a specific time, not too fast and also too late. Several researchers said that the beginning of Dawn prayer in Indonesia was too fast and required re-assessment. The main factor related to determining prayer times is the height of the sun (dip). Some scientists and ulama' have a different opinion about the value of the altitude at true dawn appears, ranging from -14° to-20°. This research uses image processing techniques using the Canny method of edge detection by utilizing the Graphical User Interface (GUI) feature of the Matlab Software. Data was collected in Dampit Sub-District, Malang Regency, and ten days every half hour before dawn prayer times based on the Ministry of Religion schedule until half an hour after that. The results of the research can detect images well and obtained dip values ranging from -17.588˚ to -20.8194˚ and time ranges from 04.25 to 04.12 WIB. From the ten data, the earliest dip value was taken as a result of research for caution because it was feared that the dawn would be obstructed by cloudiness, namely when the dip was greater than -20.8194˚. The accuracy value of the dawn time in Dampit Sub-District compared to the Ministry of Religion has a difference of one to ten minutes. However, the dip range of the research results with the dip used by the Ministry of Religion has the same value, namely -20˚.

Astrophotography and image processing techniques were introduced as a solution to the problem of determining the beginning dawn time. The results of some research were different with Ministry Religion Affairs and raise doubts for some Muslims then need to require re-verification. Astrophotography, a special method of photography, is recording images of astronomical objects such as the moon, stars, and other celestial bodies. The astrophotography technique is used for the object of the emergence of dawn rays with the assumption that the image before and after the appearance of dawn will have different pixel values. Then, a combination of astrophotography and image processing techniques is used to analyze pixel changes to identify the beginning of dawn. The image processing technique used is edge detection. Edges correspond to changes in pixel intensity. The easiest way to detect the beginning of dawn is to apply a filter that highlights this change in intensity in both directions: horizontal (x) and vertical (y). An edge detection filter "sadiq filter" is modeled as a result of the development of the Sobel and canny filters. Sadiq filter has been applied to the dawn data in Labuan Bajo and can distinguish the image before and after dawn well. It is hoped that the "sadiq filter" can be developed into a filter from an application or software so that it can be used by the wider community to solve the problem of determining the early morning prayer time. An edge detection filter "sadiq filter" is modeled as a result of the development of the Sobel and canny filters. Sadiq filter has been applied to the dawn data in Labuan Bajo and can distinguish the image before and after dawn well. It is hoped that the "sadiq filter" can be developed into a filter from an application or software so that it can be used by the wider community to solve the problem of determining the early morning prayer time. An edge detection filter "sadiq filter" is modeled as a result of the development of the Sobel and canny filters. Sadiq filter has been applied to the dawn data in Labuan Bajo and can distinguish the image before and after dawn well. It is hoped that the "sadiq filter" can be developed into a filter from an application or software so that it can be used by the wider community to solve the problem of determining the early morning prayer time.