Method for compressing an image, characterised in that: - an index representative of a distribution of light intensity values of pixels of at least all of a brightness layer of the image is calculated, said index being calculated as: FD 2 = ∑ k = 0 255 max n k − 0,4 ∗ n k − 1 + n k + 1 − 0,1 ∗ n k − 2 + n k + 2, 0 N 2 where: o the number n(k) represents the number of pixels having the brightness value k in said brightness layer; o N represents the total number of pixels of the image; then, - according to said index, the image is classified in one of the following three categories: o a first category if the image is of a graphic type; o a second category if the image is of a high-contrast type; o a third category if the image is of a low-contrast type; and, - a compression processing type is selected according to the category of the image: o if the image is of the first category, a compression processing comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer is selected; o if the image is of the third category, a frequency type compression processing is selected; o if the image is of the second category, the following are selected: ■ for lossless compression, a processing is used comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer, and, ■ in the other cases, a frequency type compression processing is used. - an index representative of a distribution of light intensity values of pixels of at least all of a brightness layer of the image is calculated, said index being calculated as: FD 2 = ∑ k = 0 255 max n k − 0,4 ∗ n k − 1 + n k + 1 − 0,1 ∗ n k − 2 + n k + 2, 0 N 2 where: o the number n(k) represents the number of pixels having the brightness value k in said brightness layer; o N represents the total number of pixels of the image; then, o the number n(k) represents the number of pixels having the brightness value k in said brightness layer; o N represents the total number of pixels of the image; then, - according to said index, the image is classified in one of the following three categories: o a first category if the image is of a graphic type; o a second category if the image is of a high-contrast type; o a third category if the image is of a low-contrast type; and, o a first category if the image is of a graphic type; o a second category if the image is of a high-contrast type; o a third category if the image is of a low-contrast type; and, - a compression processing type is selected according to the category of the image: o if the image is of the first category, a compression processing comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer is selected; o if the image is of the third category, a frequency type compression processing is selected; o if the image is of the second category, the following are selected: ■ for lossless compression, a processing is used comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer, and, ■ in the other cases, a frequency type compression processing is used. o if the image is of the first category, a compression processing comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer is selected; o if the image is of the third category, a frequency type compression processing is selected; o if the image is of the second category, the following are selected: ■ for lossless compression, a processing is used comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer, and, ■ in the other cases, a frequency type compression processing is used. ■ for lossless compression, a processing is used comprising a difference between the original value of a pixel of the brightness layer and the decompressed value of a pixel adjacent to said layer, and, ■ in the other cases, a frequency type compression processing is used.