Abstract The optical density of an X-ray photograph can only be measured after film development. If the developed film does not meet quality standards, parameters must be adjusted and the optical density re-measured, requiring additional time and effort. In contrast, digital radiography (DR) images allow direct reading of gray-scale values on the display screen. By fine-tuning parameters like window width, window level, and contrast, high-quality images can be efficiently obtained. To explore the relationship between X-ray photograph density and DR image gray-scale values, we used 256-level grayscale test images as research subjects. Gray-scale values of DR images and density values of laser-printed photographs were analyzed for correlation and regression. Results showed a strong linear relationship between DR image gray-scale values and photograph density values. Verification was conducted across different anatomical regions and X-ray conditions, confirming that DR image gray-scale values reliably predict laser-printed photograph density values.