Face Detection Method

A method of defining a skin tone in an image for face detection, the image comprising a plurality of pictures elements, each picture element having a plurality of colour components in a predetermined colour space, the method comprising:

• determining an extended range of colour component values, in the predetermined colour space, in which a skin tone area is likely to be detected;
• defining a plurality of intervals of colour component values, in the predetermined colour space, covering at least part of the extended range;
• scanning each of the plurality of intervals to detect a skin tone area;
• and
• if at least one skin tone area is detected in at least one interval:
• selecting at least some of the intervals in which at least one skin tone area is detected;
• selecting candidate limited ranges of colour component values in the colour space from the selected intervals;
• performing a face detection on at least one skin tone area in one or more of the chosen candidate limited ranges;
• and
• selecting a chosen candidate limited range based on the number of faces detected during the face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces.

A method of face detection in a video sequence comprising a plurality of images, each image comprising a plurality of picture elements, each picture element having a plurality of colour components in a predetermined colour space, the method comprising:

• in a first phase, for at least one first image:
• determining an extended range of colour component values, in the predetermined colour space, in which a skin tone area is likely to be detected;
• defining a plurality of intervals of colour component values, in the predetermined colour space, covering at least part of the extended range;
• scanning each of the plurality of intervals to detect a skin tone area;
• and
• if at least one skin tone area is detected in at least one interval:
• selecting at least some of the intervals in which at least one skin tone area is detected;
• selecting candidate limited ranges of colour component values in the colour space from the selected intervals;
• performing a face detection on at least one skin tone area in one or more of the chosen candidate limited ranges;
• and
• selecting a chosen candidate limited range based on the number of faces detected during the face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces;
• and
• in a second phase:
• for one or more of the images in the sequence, performing a face detection in the same candidate limited range as the chosen candidate limited range for the at least one first image.

A computer program product comprising a non-transitory computer readable medium having stored thereon one or more stored sequences of instructions that are loadable into a processor and which, when executed by the processor, cause the processor to:

• determine an extended range of colour component values, in a predetermined colour space, in which a skin tone area is likely to be detected;
• define a plurality of intervals of colour component values, in the predetermined colour space, covering at least part of the extended range;
• scan each of the plurality of intervals to detect a skin tone area;
• and
• if at least one skin tone area is detected in at least one interval:
• select at least some of the intervals in which at least one skin tone area is detected;
• select candidate limited ranges of colour component values in the colour space from the selected intervals;
• perform a face detection on at least one skin tone area in one or more of the chosen candidate limited ranges;
• and
• select a chosen candidate limited range based on the number of faces detected during the face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces.

A computer program product comprising a non-transitory computer readable medium having stored thereon one or more stored sequences of instructions that are loadable into a processor and which, when executed by the processor, cause the processor to:

• in a first phase, for at least one first image:
• determining an extended range of colour component values, in the predetermined colour space, in which a skin tone area is likely to be detected;
• defining a plurality of intervals of colour component values, in the predetermined colour space, covering at least part of the extended range;
• scanning each of the plurality of intervals to detect a skin tone area;
• and
• if at least one skin tone area is detected in at least one interval:
• selecting at least some of the intervals in which at least one skin tone area is detected;
• selecting candidate limited ranges of colour component values in the colour space from the selected intervals;
• performing a face detection on at least one skin tone area in one or more of the chosen candidate limited ranges;
• and
• selecting a chosen candidate limited range based on the number of faces detected during the face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces;
• and
• in a second phase:
• for one or more of the images in the sequence, performing a face detection in the same candidate limited range as the chosen candidate limited range for the at least one first image.

A device for defining a skin tone in an image for face detection, the image comprising a plurality of picture elements, and each picture element having a plurality of colour components in a predetermined colour space, the device comprising:

• a skin tone detector configured to:
• determine an extended range of colour component values, in the colour space, in which a skin tone area is likely to be detected;
• define a plurality of intervals of colour component values, in the colour space, covering at least part of the extended range;
• scan at least some of the plurality of intervals to detect a skin tone area;
• and,
• a facial feature detector configured to:
• if at least one skin tone area is detected in at least one interval:
• select at least some of the intervals in which at least one skin tone area is detected;
• define candidate limited ranges of colour component values in the colour space, from the selected intervals;
• perform a face detection on at least one skin tone area in at least some of the candidate limited ranges;
• and
• select a chosen candidate limited range based on the number of faces detected during said face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces.

A portable electronic apparatus comprising a device for defining a skin tone in an image for face detection, the image comprising a plurality of picture elements, and each picture element having a plurality of colour components in a predetermined colour space, the device comprising:

• a skin tone detector configured to:
• determine an extended range of colour component values, in the colour space, in which a skin tone area is likely to be detected;
• define a plurality of intervals of colour component values, in the colour space, covering at least part of the extended range;
• scan at least some of the plurality of intervals to detect a skin tone area;
• and,
• a facial feature detector configured to:
• if at least one skin tone area is detected in at least one interval:
• select at least some of the intervals in which at least one skin tone area is detected;
• define candidate limited ranges of colour component values in the colour space, from the selected intervals;
• perform a face detection on at least one skin tone area in at least some of the candidate limited ranges;
• and
• select a chosen candidate limited range based on the number of faces detected during said face detection, wherein the chosen candidate limited range is the selected interval leading to the maximum number of detected faces.