Wyniki wyszukiwania - BazTech

Ograniczanie wyników

1 Duda J.

1 2011

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: sector scanning sonar

Sortuj według:

Ogranicz wyniki do:

Zastosowanie techniki HDR do obrazów pozyskiwanych z sektorowego sonaru skanującego

Duda J.

Biuletyn Wojskowej Akademii Technicznej

2011

Vol. 60, nr 3

291-306

Obrazy pozyskiwane za pomocą sonarów sektorowych mają często ograniczoną głębokość bitową do ośmiu bitów. Powoduje to szereg restrykcji związanych z percepcją obrazów sonarowych, jak również z późniejszym ich przetwarzaniem. W artykule przedstawione zostały badania związane z zastosowaniem techniki uzyskiwania obrazów o szerokim zakresie tonalnym (High Dynamic Range) do obrazów sonarowych. Zastosowanie techniki HDR pozwala na zwiększenie ilości informacji przenoszonej przez obraz sonarowy i brak konieczności wyboru między lepszą reprezentacją dna czy też obiektów się na nim znajdujących.

The images obtained with sector scanning sonar have often bit depth limited to eight bits. It causes a lot of limitations related with sonar images perception and also later with their transformation. Already during sonar images registration process, the operator must decide what is more important to him. The operator must choose between good visibility of bottom or objects located on it. Such is a characteristic property of low dynamic range (LDR) images. In other words, operator has to choose between better representation of bottom or the objects, what is realized by changing the gain of the acoustic signal. Selection between better representation of the bottom or the objects is performed by increasing or reducing the strengthening of the acoustic wave generated by the sonar transducer. Increase in the strength of the acoustic wave causes additional distortion on the sonar image which can be observed particularly near the sonar transducer. These distortions are also produced by the presence of the object, growing if the object is nearby the sonar transducer. If the sonar acoustic wave is too strong, then induced distortions cause poor visibility of sonar images. Using the transformations of the low dynamic range sonar images to improve the poor visibility of particular elements often causes an additional loss of information. As a result, the image can become unreadable. Unfortunately, there is no possibility of artificial enhancement of the information contained in the image. The article presents the research related to HDR images using for the sonar images. The HDR method is used in photography to improve their perception. Using images with different value of exposition can be presented by both dark and bright elements. HDR images characterize a good object resolution. Nowadays, HDR images were used mainly in photography. In the article, the HDR method was applied for the first time to the sector scanning sonar images. In the sonar HDR images, the exposure value was replaced by the strength of the sonar acoustic signal. Using the HDR method in photography increases the aperture or decreases photo array sensitivity effect on the value of exposition. Inversely, to reduce exposure we must decrease the aperture or increase sensitivity of the matrix. For the sonar images there is only one parameter influencing the exposure value, namely the gain of the sonar acoustic signal. For the HDR sonar images, increasing exposure is equivalent to reduction of the gain acoustic signal and decreasing exposure with an enlargement of the gain acoustic signal. Using three images of different exposure during a single sonar registration, we obtain the high dynamic range sonar image. In contrary to the side scan sonar, which has to be towed several times over the same area, it allows to locate the sector scanning sonar on a tripod at the bottom. For this reason, the sector scanning sonar location does not occurr the distortion associated with the movement of the vessel and waving. Because the registered sonar images are not shifted mutually, there is not necessity to match them what simplify HDR sonar images process realization. The HDR technique can also be applied to images obtained from side-scan sonar. However, the main problem to have HDR images is obtaining images from the same place and their matching. Using the HDR method allows to enlarge the quantity of information contained in sonar image by increasing the bit width of the sonar image, namely from eight to sixteen bit. Obtaining more values and regular values distribution on the HDR sonar image histogram results in no necessity of choice between better representation of bottom or object located on the sonar image.