Process of identification of shadows in an image and image obtained using the process
View Patent ↗The invention relates to a process of shadow identification in a digital image. The digital image comprises a set of image points that can be located in a plane of the image, with each image point being associated with a color and brightness. The color is defined by chromatic components that can be located in the color space of an acquisition system, and the brightness is determinable from the chromatic components. According to the process of the present invention, for each image point, the brightness is determined; color standardization is carried out, leading to standardized chromatic components r, g, b; a chromatic brightness is determined from the standardized chromatic components r, g, b; and the chromatic brightness is compared with the brightness, to identify the presence of a shadow on the relevant image point.
1. A process of identifying a shadow in a digital image, the digital image comprising a set of image points that can be located in a plane of said image, each image point being associated with a color and brightness, the color being defined by chromatic components that are locatable in a color space of an acquisition system, the brightness being determinable from said chromatic components, wherein for each image point the process comprises the steps of,
determining a brightness;
performing a color standardization to provide standardized chromatic components r, g, b;
determining a chromatic brightness from the standardized chromatic components r, g, b; and
comparing the chromatic brightness with the brightness of each image point to identify a presence of a shadow on a relevant image point.
2. A process according to claim 1 , wherein said brightness determining step comprises determining a brightness of each image point by a component Y in an XYZ color space system, a color of said point having X, Y, Z components in said system.
3. A process according to claim 2 , wherein the XYZ color space is defined independently of material characteristics related to physical constraints of the acquisition system.
4. A process according to claim 2 , wherein the XYZ color space is a standardized color space.
5. A process according to claim 4 , wherein the standardized color space is defined according to a predetermined standard.
6. A process according to claim 1 , wherein said step of performing color standardization comprises the steps of:
determining X, Y, Z components of a color in a three-dimensional system of a standardized XYZ color space;
calculating x, y, z components of the standardized color in the three-dimensional system of the standardized XYZ color space by dividing the X, Y, Z components, respectively by a sum of the X,Y,Z components; and
determining the chromatic components r, g, b of the standardized color in a chromatic RGB color space from the x, y, z components of the standardized color.
7. A process according to claim 1 , wherein the chromatic brightness of an image point is determined from the chromatic components r, g, b, of the standardized color according to a process similar to the determination of the brightness.
8. A process according to claim 1 , wherein the presence of a shadow on the relevant image point is identified if the chromatic brightness is more than the brightness.
9. A process according to claim 1 , wherein the identification of the presence of a shadow for each image point enables a mapping of the shadow in the image to be produced.
10. An image produced using digital processing between a starting image and a mapping or mask of the starting image, the mapping or mask being obtained by a process according to claim 9 .
11. A process according to claim 1 , wherein the identification of the presence of a shadow for each image point enables a mask of shadowed and non-shadowed zones in the image to be produced.
12. An image produce using digital processing between a starting image and a mapping mask of the starting image, the mapping or mask being obtained by a process according to claim 11 .