Forensic estimation of gamma correction in digital images
ABSTRACT In the digital era, digital photographs become pervasive and are frequently used to record event facts. Authenticity and integrity of such photos can be ascertained by discovering more information about the previously applied operations. In this paper, we propose a forensic scheme for identifying and reconstructing gamma correction operations in digital images. Statistical abnormity on image grayscale histograms, which is caused by the contrast enhancement, is analyzed theoretically and measured effectively. Graylevel mapping functions involved in gamma correction can be estimated blindly. Experiments both on globally and locally applied corrected images show the validity of our proposed gamma estimation algorithm.
- SourceAvailable from: Javier Vazquez-Corral
- "Let us also remark that none of the single-image methods, neither the blind gamma estimation , , , nor the CRF estimation ones , , are capable of improving their performance if extra images are available. III. "
Article: Simultaneous Blind Gamma Estimation[Show abstract] [Hide abstract]
ABSTRACT: Blind gamma estimation is the problem of estimating the gamma function that is applied to a linear image both for perceptual reasons and for the compensation of the non-linear behavior of displays. Gamma values change both inter- and intra-camera. In the latter case, the change comes from the use of different scene settings. In this letter we propose a new approach that relies on the use of more than a single image from the same scene. We estimate the gammas for all the different images at the same time with a method based on exploiting the structure of the standard in-camera processing pipeline. Our results improve over the state-of-the-art.IEEE Signal Processing Letters 09/2015; Accepted(9). DOI:10.1109/LSP.2015.2396299 · 1.64 Impact Factor
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- "The prior methods – fail to detect contrast enhancement in the previously middle/low quality JPEG-compressed images. To investigate the reasons behind such ineffectiveness, the impact of JPEG compression on histograms is analyzed. "
ABSTRACT: As a retouching manipulation, contrast enhancement is typically used to adjust the global brightness and contrast of digital images. Malicious users may also perform contrast enhancement locally for creating a realistic composite image. As such it is significant to detect contrast enhancement blindly for verifying the originality and authenticity of the digital images. In this paper, we propose two novel algorithms to detect the contrast enhancement involved manipulations in digital images. First, we focus on the detection of global contrast enhancement applied to the previously JPEG-compressed images, which are widespread in real applications. The histogram peak/gap artifacts incurred by the JPEG compression and pixel value mappings are analyzed theoretically, and distinguished by identifying the zero-height gap fingerprints. Second, we propose to identify the composite image created by enforcing contrast adjustment on either one or both source regions. The positions of detected blockwise peak/gap bins are clustered for recognizing the contrast enhancement mappings applied to different source regions. The consistency between regional artifacts is checked for discovering the image forgeries and locating the composition boundary. Extensive experiments have verified the effectiveness and efficacy of the proposed techniques.IEEE Transactions on Information Forensics and Security 03/2014; 9(3):515-525. DOI:10.1109/TIFS.2014.2300937 · 2.07 Impact Factor
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- "As a main branch of the digital forensics technique, image manipulation forensics technique focuses on detecting the image alterations blindly. Currently, plenty of forensics algorithms have been proposed to detect the image alterations including content-changing operations such as image splicing   , and content-preserving ones: resampling   , compression   and image enhancement, i.e. contrast adjustment    , sharpening  and median filtering  . "
ABSTRACT: Recently, several new resampling operators have been proposed and successfully invalidate the existing resampling detectors. However, the reliability of such anti-forensic techniques is unaware and needs to be investigated. In this paper, we focus on the forensic identification of digital image resampling operators including the traditional type and the anti-forensic type which hides the trace of traditional resampling. Various resampling algorithms involving geometric distortion (GD)-based, dual-path-based and postprocessing-based are investigated. The identification is achieved in the manner of semi non-intrusive, supposing the resampling software could be accessed. Given an input pattern of monotone signal, polarity aberration of GD-based resampled signal's first derivative is analyzed theoretically and measured by effective feature metric. Dual-path-based and postprocessing-based resampling can also be identified by feeding proper test patterns. Experimental results on various parameter settings demonstrate the effectiveness of the proposed approach.Forensic science international 09/2011; 216(1-3):29-36. DOI:10.1016/j.forsciint.2011.08.012 · 2.12 Impact Factor