An experiment was carried out to evaluate the perceptibility and the acceptability of colour differences between pairs of CRT images. Four images were used. For each image, a series of images were systematically rendered following four directions: lightness, chroma, mixed lightness and chroma, and hue using different functions. The effects of rendering were assessed by a panel of observers. The results were used to test the performance of different colour difference equations. In addition, the perceptibility threshold and the acceptability tolerance for each formula were determined.