## 1 Introduction  
Internal defects are the major sources of composite failures in FRP structures and originate from manufacturing (delamination, voids, porosity, fiber wrinkles, etc.) and/or from in-service events (impact or fatigue damage, micro-cracks, debonding, delamination, erosion, etc.). A combination of contemporaneous voids, matrix cracks, and multiple delamination may occur, and structural integrity is verified using nondestructive testing (NDT) methods to determine the damage risk [1].  
Thermal methods are most effective for thin laminates or for defects near the surface and the passive or active approach are adopted. In active IRT methods, an external stimulus is applied to specimen surface, in order to induce relevant thermal contrasts between regions of interest and these techniques include pulsed thermography (PT) as valid robust technique for checking the integrity of structures [2; 3] and consists of rapidly heating the specimen recording the temperature decay curve; the free-defect material conducts heat more efficiently than defective zones, where heat is either absorbed, or reflected, indicating the quality state of the inspected area [4].  
Active IR-thermographic methods such as cooling down thermography (CDT) [5] or long pulsed thermography (LPT) [6; 7] give satisfactory results for similar defects in composites. In this paper, PT thermography in the range of long pulses is explored, even that heat accumulation phenomenon may occur for subsurface defects. The CDT method represents an interesting and valid ND approach where a previous thermal excitation in an oven allows a uniform temperature through thickness and could be applied on CFRP plates, especially in the case of deeper defects.  
However, this is not a suitable technique for wider structural component of the authors' lack of experience and need of a large climatic chamber. However, future CDT tests will be considered.  
Raw thermal imaging from PT investigation is usually not suitable for a precise material evaluation and a quantitative analysis of the registered temperatures is required to better determine the dimension, depth, and defect shape. Signal levels associated with subsurface anomalies can be lost in the thermal data noise [8] and proper different post-processing methods are used to improve the signal-to-noise (SNR) content of recorded data.  
Several processing methods have been developed to improve delamination characterization for thermographic tools [9] and introduce automatic images analysis, actual main goal for thermographic inspection, providing a pass-or-fail diagnostic to the operator [10; 11]. The literature on thermal image-processing proposes different algorithms developed to improve detect detection from thermal maps [3; 12] and, in the present paper, a different image-processing method is introduced, where defects are automatically visualized on thermal contrast maps for CFRP specimens and experimental procedure is optimized, in order to facilitate inspections for operators with automatic and accurate post-processing, at the same time with good reliability level to be guaranteed.  
Since thermography is considered as an emerging technology, real component thermal contrast maps were verified using the well-established ultrasonic c-scanning technique, as explained in other works [13] for unknown damage area evaluation on composites, using modern phased array probe; several authors [14; 15; 16] make use of ultrasonic NDI systems for the reliable and effective detection of delaminations, the primary important damage mode for aeronautical applications, where fatigue and impact failures are likely to occur [17].