Method for determining a colour value of an object in an image

A device for determining an apparent colour value of pixels corresponding to a subpart of an object represented in an image, referred to as the acquired image, wherein the device comprises electronic circuitry adapted for:

• estimating a geometric distortion model of said object in the acquired image compared with a reference model of the object, the object in the acquired image being a distorted version of the object in the reference model, the geometric distortion model allowing passing from the object in the acquired image to the object in the reference model and conversely;
• from the geometric distortion model and the reference model of the object, determining a position of the subpart in the acquired image, called acquired subpart, from a position of the same subpart in the reference model, called model subpart, and determining a zone of the acquired image, referred to as the reference zone, situated in a predetermined vicinity of the acquired subpart, from the same zone in the reference model, referred to as a blank zone, of the reference model of the object in the acquired image, the blank zone being associated with a predetermined colour value in the reference model of the object;
• and
• determining an apparent colour value of the pixels of the subpart, from a colour value of at least one pixel of the reference zone.

A device for determining that a mark has been applied to a subpart of a document, said document comprising at least one subpart on which a mark can be applied, an image representing the document, referred to as the acquired image, having been acquired by an image acquisition device, wherein the device comprises electronic circuitry adapted for:

• for each subpart of the document on which a mark can be applied, determining an apparent colour value of the pixels of acquired image corresponding to the subpart by applying to the subpart a method comprising:
• estimating a geometric distortion model of said document in the acquired image compared with a reference model of the document, the object in the acquired image being a distorted version of the object in the reference model, the geometric distortion model allowing passing from the object in the acquired image to the object in the reference model and conversely;
• from the geometric distortion model and the reference model of the document, determining a position of the subpart in the acquired image, called acquired subpart, from a position of the same subpart in the reference model, called model subpart, and determining a zone of the acquired image, referred to as the reference zone, situated in a predetermined vicinity of the acquired subpart, from the same zone in the reference model, referred to as a blank zone, of the reference model of the object in the acquired image, the blank zone being associated with a predetermined colour value in the reference model of the object;
• and
• determining an apparent colour value of the pixels of the subpart, from a colour value of at least one pixel of the reference zone;
• and
• deciding, for each subpart of the document on which a mark can be applied, that a mark has been applied on said subpart when a proportion of the pixels corresponding to the subpart having a colour value, referred to as the pixel colour value, close to the apparent colour value, is below a first predetermined threshold, a pixel colour value being close to the apparent colour value when a difference between said pixel colour value and the apparent colour value is less than a predetermined difference.