## 4 Dataset  
In this study, a new dataset consisting of images and laser reflection data was created to determine the level of fish freshness. In order to take fish images under controlled conditions, a special experimental setup was constructed, as shown in Figure 3a. A rectangular prism was designed for the experimental setup, and a camera was placed on its upper part to capture the fish directly. A PVC plate was placed 60 cm below the camera, and a black fabric that did not reflect light was fixed on the upper surface. The black fabric was used to create contrast in the image and to render the details of the fish clearly visible. In the imaging phase, the fish were placed on the black fabric in a fixed position, and images were taken from both surfaces. The lighting conditions were kept constant during this process. Figure 3: (**a**) Experimental setup for capture of fish images under controlled conditions, (**b**) laser sensor layout, and (**c**) measurement of laser reflection data from fish. Figure 2: Schematic representation of the interaction of laser light with fish tissue. The high-precision Time-of-Flight (ToF) TMF8821 laser sensor, manufactured by ams OSRAM AG (Tobel-bader Strasse 30, 8141 Prematatten, Styria, Austria), was used to obtain fish reflection data. This sensor sends laser light to the target and provides a histogram of the number of photons reflected from the target. The ToF sensor has a 4 \(\times\) 4 multizone, dynamically configurable scanning field. The sensor contains a low-power vertical cavity surface emitting laser (VCSEL) with a single wavelength of 940 nm. As shown in Figure 3b, the laser module assembly was designed in a conical shape and fixed to a 3-cm-high assembly created with a 3D printer. Figure 3c shows the measurement procedure used to obtain laser reflection data from fish. The reflection data obtained from the laser module were transferred to the computer environment with the Arduino UNO development board. Before starting the measurements, the laser sensor was configured as 3 \(\times\) 3 zones. In this way, laser reflection data were obtained from nine different regions of the fish, close to each other and at the same time during each measurement. The measurement region was limited to the abdominal (ventral) mid-body area of the fish to ensure that all nine laser zones consistently fell within the body surface. Since the laser sensor captured data from adjacent zones simultaneously, narrow anatomical areas such as the eye or tail posed a risk of some beams potentially falling outside the fish. In this study, 130 mackerel fish were used in the dataset created to evaluate fish freshness. Approximately six hours elapsed from the time that the fish were caught and then shocked, stored, purchased, and prepared for measurement. Throughout the 3-day experimental period, the fish were stored under controlled laboratory conditions at a constant temperature of approximately 4 \({}^{\circ}\)C. During each measurement session, fish were taken out from the cooling chamber in small groups, measured quickly, and immediately returned to cold storage. This procedure minimized exposure to external environmental factors. The relative humidity was maintained in the range of 40% to 60%, and the measurement area was arranged to prevent temperature fluctuations. Additionally, ventilation was provided to ensure stable air circulation and maintain temperature consistency. Each fish was measured at 24 h intervals corresponding to Day 1, Day 2, and Day 3. Representative images illustrating the visual changes in two different mackerel samples over this period are presented in Figure 4. For each session, data were collected from both the front and back surfaces of the fish. Although the total planned number of paired samples was 780, some samples were excluded due to synchronization issues during simultaneous image and laser acquisition. As a result, two samples were removed from Day 1 and four samples each from Day 2 and Day 3, resulting in a final total of 770 matched image and laser samples.