A method of measuring the degradations in a digitized image, which are introduced during the encoding of the image is provided. The method consists in: retrieving the block decomposition of the image used during the encoding thereof; offsetting the coding grid in relation to the image such as to define an analysis block decomposition of the image, whereby each analysis block covers a boundary between two adjacent blocks; applying a transform calculation to the pixel data of the image which is encoded using the offset coding grid; extracting the transformed coefficients obtained for each analysis block, coefficients which are likely to be affected by a block effect; applying an inverse transform calculation to the extracted transformed coefficients in order to determine the pixel data of each analysis block; and, for each analysis block, calculating a degradation indicator and, subsequently, the degradation of the image from the degradation indicators for each analysis block.