Digital image processing method having an exposure correction based on recognition of areas corresponding to the skin of the photographed subject

a digital image and processing method technology, applied in image data processing, character and pattern recognition, instruments, etc., can solve problems such as image quality, flash device, and generation of sub-optimal photographs

Inactive Publication Date: 2005-01-27
STMICROELECTRONICS SRL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

As is well known, one of the main problems limiting photographic image quality involves the generation of sub-optimal photographs due to the wrong exposure to light of the photographed subject.
This problem is particularly suffered in portable devices such as mobile phones, wherein several factors concur in obtaining photographs that are wrongly exposed: the smallness of the available optical device, the lack of a flash device and the like.
Although advantageous under many aspects, these prior art techniques have several drawbacks mainly linked to the fact of being independent from the visual content of the photographed images.
Although advantageous under several aspects, these prior art techniques are not very effective in the case of portable devices like mobile phones for which the photographic images are often backlit and they are mainly focused on human figures, when the user uses the image transmission for videophony, as shown in FIG. 3.

Method used

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  • Digital image processing method having an exposure correction based on recognition of areas corresponding to the skin of the photographed subject
  • Digital image processing method having an exposure correction based on recognition of areas corresponding to the skin of the photographed subject
  • Digital image processing method having an exposure correction based on recognition of areas corresponding to the skin of the photographed subject

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Experimental program
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first embodiment

In a first embodiment, this recognition step is substantially based on a probabilistic function.

In particular, for each pixel of an image taken in the YcrCb format a probabilistic slicing is prepared to evaluate if this pixel must be classified as belonging to the subject skin. Based on this slicing, a new image is thus processed with a normalized grey scale, wherein the subject skin is highlighted as indicated in FIGS. 5A-6C on two different photographic images which depict human subjects.

Based on this first embodiment of the recognition step of the photographed subject skin, the image pixels with higher grey values are considered as belonging to the skin of the photographed subject.

The areas being detected by using this first embodiment of the recognition step of the skin of the photographed subject on an image shown in FIG. 5A are shown in Figure and 5C. Similarly, FIG. 6C highlights areas of the image of FIG. 6A corresponding to the skin of another photographed subject, acc...

second embodiment

In a second embodiment, the recognition step of the image areas corresponding to the skin of the photographed subject is substantially based on a single threshold area and it provides an RGB-format image processing in order to produce a chrominance slicing histogram starting from normalized channels r and g as described in the article by Soriano et al. entitled “Skin Color Modeling Under Varying Illumination Conditions Using the Skin Locus for Selecting Training Pixels”, Real-time Image Sequence Analysis (RISA2000, August 31-September 1, Finland), which is hereby incorporated by reference in its entirety. In particular, the normalized channels r and g are defined as:

r=R / (R+G+B)  (10)

g=G / (R+G+B)  (11)

The resulting bidimensional histogram shows the chrominance slicing in the image and the areas having the right human skin chrominance slicing are thus detected by applying a single threshold area. In particular, the pixels of the processed image belonging to the threshold area are cl...

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Abstract

A digital image processing method includes extracting chromatic information of an image taken by an image taking device and related to a human subject; detecting visually interesting regions; and exposure correcting of the taken image by normalizing a grey scale of the taken image based on the visually interesting regions. Advantageously, the method includes recognizing areas corresponding to the skin of the subject, these areas being used as the visually interesting regions for the exposure correction step.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image processing method. The invention relates particularly, but not exclusively, to an image processing method of human subjects being photographed by portable image taking devices, particularly of backlit subjects and the following description is made with reference to this field of application for convenience of illustration only. 2. Description of the Related Art As is well known, one of the main problems limiting photographic image quality involves the generation of sub-optimal photographs due to the wrong exposure to light of the photographed subject. This problem is particularly suffered in portable devices such as mobile phones, wherein several factors concur in obtaining photographs that are wrongly exposed: the smallness of the available optical device, the lack of a flash device and the like. Moreover, the portable device nature and the traditional use of the photographs ...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G06K9/00G06T5/40H04N9/64H04N1/407H04N1/46H04N1/60
CPCG06K9/00234H04N1/6027G06T5/40G06T5/007G06V40/162
Inventor MESSINA, GIUSEPPEBATTIATO, SEBASTIANOCASTORINA, ALFIOPLAZA, LAURENT
Owner STMICROELECTRONICS SRL
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