In this work we present a method to calculate the spectrum of the fundamental primaries of a digital camera from the experimental knowledge of its spectral sensitivities. The color triangle of the camera, linked to the chromaticities of its primaries, is compared below with the theoretical options of Ives-Abney-Yule and MacAdam. Therefore, this is a simple method to determine at first approximation the color gamut of an input device. This methodology may apply to any kind of camera and scanner. Results obtained with a particular digital camera (Sony DXC-930P) show that the red and purple zone, like the blue-green zone but in minor extend, is not well filled by this input device.