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정수기반 웨이블릿 변환을 이용한 통합된 유 / 무손실 의학영상압축
안창범(Ahn C . B .),송영철(Song Y . C .),고형화(Koh H . H .),안용현(Ahn Y . H .) 한국화상학회 1998 한국화상학회지 Vol.4 No.1
A unified lossy to lossless compression algorithm is developed using integer-based reversible wavelet transforms. The proposed algorithm is based on a pre-quantization, integer-based wavelet transform, and a bit plane coding of the wavelet bands with QM coder. An improved pre-quantization scheme is proposed with which number of gray levels after pre-quantization is the same as that in the original image. An optimal encoding order for the wavelet bands in both spatial frequency domain and bit planes are devised. Prom simulation, reconstructed image by the proposed algorithm shows higher peak signal-to-noise ratio (PSNR) compared to those obtained by a float-point-based wavelet transform (Daubechies) and the JPEG. Peak errors in the reconstructed images by the integer-based wavelet transform are also much lower than those obtained by the JPBG and the float-point-based wavelet coding. In near lossless compression, lossless encoding of the wavelet coefficients of the pre-quantized image shows higher PSNR than those with bit rate control by the bit plane-band ordering of the wavelet coefficients without pre-quantization. Using pre-quantization, peak error can be easily controlled, which may be an important feature in medical image compression.
JPEG 점진적 확장 코딩을 이용한 핵자기 공명 영상 압축
안창범(Ahn C . B .),윤기병(K . B . Yoon) 한국화상학회 1995 한국화상학회지 Vol.1 No.1
The JPEG (Joint Photographic Experts Group) standard which was accepted as a compression method in the Digital Imaging and Communications in Medicine (DICOM) standard recently is tested with a set of magnetic resonance (MR) images with 8 bits/pixel and 12 bits/pixel precisions. Due to the lossy character of the DCT-based JPEG compression, its application to medical image compression has been limited. for head sections of MR images, compression ratios of more than 10 are obtained without noticeable image degradation. The performance of the JPEG coding is compared to existing full-frame bit-allocation technique proposed for the radiological image compression. From comparison, the JPEG standard achieves higher compression with high signal-to-noise ratio. Reconstructed images by the JPEC standard also show better subjective image quality with less Gibb`s artifact. The progressive JPEG coding may be useful in tele-radiology when data is transmitted through slow public communication channel.
자기공명영상의 신호대잡음비 향상을 위한 다중 템플릿 적응 필터링
안창범(Ahn C . B .),송영철(Song Y . C .),박대준(Park D . J .) 한국화상학회 1997 한국화상학회지 Vol.3 No.1
In this paper, a local shape adaptive template filtering is proposed for an enhancement of signal-to-noise ratio in magnetic resonance imaging with little degradation of resolution. Uulike conventional filtering where template size and shape are fixed, multiple templates are defined and optimal template among the multiple templates is selected and applied in pixel-by-pixel basis. By the proposed scheme, edge blurring is minimized by selecting mostly matched template, yet SNR enhancement by the filtering is fully utilized. Compared to existing two-dimensional linear least square error Inter or direction-adaptive recursive filter, the proposed shape-adaptive filter with multiple templates provides higher SNR and sharper edges for both natural images and artificial resolution phantom images.
삼차원 의학 영상에서 시각적으로 향상된 정합을 사용한 프랙탈 부호화
안창범,송영철,신흥식,Ahn, C.B,Song, Y.C,Shin, H.S 대한의용생체공학회 1996 의공학회지 Vol.17 No.3
A new three dimensional fractal coding is proposed with a perceptually enhanced matching. Since most of medical images (e.g. computed tomoyaphy or magnetic resonance images) have three dimensional characters, searching regions are extended to adjacent slices. For a perceptually enhanced matching, a high frequency boost filter is used for pre-filtering images to be encoded, and a least mean square error matching is applied to the edge enhanced Images rather than the original images. From simulation with magnetic resonance images($255\times255$, 8bits/pixel), reconstructed images by the proposed compression algorithm show much improved subjective image quality with higher peak signnal-to-noise ratio compared to those by existing fractal coding algorithms at compression ratios of about 10.
웨이블릿 변환을 이용한 무손실에 가까운 의학 영상 압축
안창범(Ahn C . B .),윤기병(Yoon K . B .) 한국화상학회 1996 한국화상학회지 Vol.2 No.1
A medical image compression using wavelet transform has been tried. Due to the flexibility in representing nonstationary image signals in both time and frequency domains and the ability in adapting to human visual characteristics, wavelet transform has unique advantages over other transforms currently used in the image compression. In the proposed wavelet based compression, original image is decomposed into multi-scalar bands, and each decomposed band is quantized with different quantization step size. For the lowest band, a predictor is designed and error signal is entropy coded. For higher scalar bands, a runlength coding for zero run is employed with Huffman coding. Prom simulation with magnetic resonance images(256×256 size, 256 graylevels) reconstructed images by the proposed algorithm show higher peak signal-to-noise ratio (PSNR) compared to those obtained by the JPEG by more than 2.4 dB in near lossless condition(CR=8~10).