Security document including a laserizable layer and a pattern for illuminating in order to color a grayscale image, and corresponding fabrication and reading methods

1. A security document comprising:

a laserizable first layer including a grayscale image formed by laserizing;

a color pattern in alignment with said grayscale image;

a second layer arranged between said laserizable first layer and said color pattern, the laserizable first layer being above the second layer, and said color pattern being below the second layer, the second layer being more opaque than the laserizable first layer;

a third layer below said color pattern, the third layer being more opaque than the laserizable first layer; and

a laserizable fourth layer below said color pattern or below said third layer, wherein the laserizable fourth layer includes an additional grayscale image formed by laserizing, wherein the additional grayscale image of the laserizable fourth layer is in alignment with said color pattern;

wherein the opacity of the second layer and the opacity of the third layer are such that when observing the security document from the top, said grayscale image appears to be colored by the color pattern only when the bottom of the security document is being illuminated.

2. A security document according to claim 1 , wherein the color pattern includes at least two elements of different colors, and the laserizable first layer is laserized while taking account of the colors of said two elements of different colors.

3. A security document according to claim 2 , wherein the color pattern is a matrix of color pixels, each pixel comprising a plurality of sub-pixels of different colors, and the grayscale image includes grayscale pixels comprising grayscale sub-pixels in alignment with the sub-pixels of different colors in the color pattern.

4. A security document according to claim 1 , wherein the laserizable first layer is a window arranged within a fifth layer that is more opaque than the laserizable first layer.

5. A security document according to claim 4 , wherein an additional pattern is formed above said fifth layer.

6. A security document according to claim 1 , wherein an additional pattern is formed below said third layer.

7. A security document according to claim 1 , wherein the grayscale image of the laserizable first layer is associated with the additional grayscale image of the laserizable fourth layer in such a manner that when observing the security document from the top, a complete colored image appears only when the bottom of the security document is being illuminated.

8. A security document according to claim 1 , wherein the third layer lacks holes.

9. A fabrication method for fabricating a security document, the method comprising:

assembling together a laserizable first layer and a second layer below the laserizable first layer, the second layer being more opaque than the laserizable first layer;

forming a color pattern below the second layer;

assembling a third layer below the color pattern, the third layer being more opaque than the laserizable first layer; and

laserizing a grayscale image within the laserizable first layer, the color pattern being in alignment with said grayscale image;

wherein a laserizable fourth layer is assembled below said color pattern or below said third layer, wherein an additional grayscale image is laserized in the laserizable fourth layer, wherein the additional grayscale image in the laserizable fourth layer is in alignment with said color pattern; and

wherein when observing the security document from the top, said grayscale image appears to be colored by the color pattern only when the bottom of the security document is being illuminated.

10. A fabrication method according to claim 9 , wherein the color pattern is formed by forming a color pattern having at least two elements of different colors, and the laserizable first layer is laserized while taking account of the colors of said two elements of different colors.

11. A fabrication method according to claim 10 , wherein the color pattern is a matrix of color pixels, each pixel comprising a plurality of sub-pixels of different colors, and the grayscale image is formed by laserizing so that it includes grayscale pixels comprising grayscale sub-pixels in alignment with the sub-pixels of different colors in the color pattern.

12. A fabrication method according to claim 9 , wherein the laserizable first layer is a window that is arranged within a fifth layer that is more opaque than the laserizable first layer.

13. A fabrication method according to claim 12 , wherein an additional pattern is formed above said fifth layer.

14. A fabrication method according to claim 9 , wherein an additional pattern is formed below said third layer.

15. A fabrication method according to claim 9 , wherein the grayscale image of the laserizable first layer is associated with the additional grayscale image of the laserizable fourth layer in such a manner that when observing the security document from the top, a complete colored image appears only when the bottom of the security document is being illuminated.

16. A fabrication method according to claim 9 , wherein the laserizable first layer is laserized while the bottom of the security document is being illuminated.

17. A method of reading a security document obtained by the method according to claim 9 , wherein the security document is illuminated from the bottom and the security document is observed from the top.

18. A fabrication method according to claim 9 , wherein the third layer lacks holes.