scholarly journals STEGANOGRAFI MENGGUNAKAN METODE DISCRETE FOURIER TRANSFORM (DFT)

2018 ◽  
Vol 4 (2) ◽  
pp. 87
Author(s):  
Yuri Ariyanto ◽  
Rizky Ardiansyah ◽  
Bias Paris
Keyword(s):  
Fourier Transform ◽  
Discrete Fourier Transform ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Change Rate ◽  
Noise Ratio

Seiring dengan kemajuan teknologi, serangan terjadi pada industri photography di mana banyak penyalahgunaan foto yang memiliki hak cipta tanpa seijin pemilik foto tersebut. Karena itulah dibuat sebuah aplikasi yang berfungsi untuk menyisipkan watermark dengan menggunakan metode DFT (Discrete Fourier Transform). Metode tersebut adalah metode matematika yang sering digunakan dalam bidang elektronika dan komputer. Metode ini secara khusus digunakan untuk menyelesaikan masalah yang berhubungan dengan frekuensi, sehingga metode ini dapat digunakan dalam bidang citra digital. Metode ini diterapkan untuk melakukan penyisipan dan ekstraksi watermark pada citra penampung. Watermark tersebut disisipkan kedalam frekuensi domain pada gambar dan akan menghasilkan output citra ber-watermark atau embeded image. Hal ini adalah untuk mencegah penyalahgunaan hak cipta, namun watermark tersebut tidak nampak secara fisik. Hal ini dilakukan selain memberikan jaminan keamanan terhadap gambar, tapi juga tidak mengurangi estetika pada gambar tersebut. Analisa yang dilakukan adalah tingkat keberhasilan proses insertion dan extraction, serangan pada citra, uji kemiripan dengan pengujian NPCR (Number of Pixel of Change Rate), UACI (Unified Averaged Changed Intensity), dan PSNR (Peak Signal-to-Noise Ratio) pada proses insertion dan extraction. DFT disimpulkan aman terhadap serangan berupa cropping, resize, dan editing. Selain itu, dihasilkan nilai presentase perubahan yang rendah pada pengujian NPCR & UACI dan nilai yang tinggi pada pengujian PSNR.

scholarly journals A New Multichannel Fourier Transform Spectrometer

1999 ◽  
Vol 170 ◽  
pp. 36-40
Author(s):  
Tyler E. Nordgren ◽  
Arsen R. Hajian
Keyword(s):  
Fourier Transform ◽  
Extrasolar Planets ◽  
Signal To Noise Ratio ◽  
Fourier Transform Spectrometer ◽  
Test Bed ◽  
Signal To Noise ◽  
Stellar Spectra ◽  
Band Emission ◽  
Noise Ratio ◽  
Ratio Scales

AbstractStellar spectra have been obtained using a multichannel Fourier Transform Spectrometer (FTS) which incorporates components of the Navy Prototype Optical Interferometer. It is well known that a FTS can provide superior wavelength stability as compared to traditional spectrometers. Unfortunately the FTS traditionally suffers from exceptionally poor sensitivity, which until now has limited its uses to sources with high fluxes and/or those with narrow band emission (e.g. the Sun, nebulae, and laboratory samples). We present stellar observations using a new FTS design which overcomes this sensitivity limitation by using a conventional multichannel spectrometer in conjunction with the FTS system. The signal-to-noise ratio of spectra from our test-bed observations are consistent with the theoretical prediction and show that for N channels the sensitivity scales like N, while the signal-to-noise ratio scales like . With this type of an instrument on a 3-m telescope and 9 000 channels we expect to be able to detect and measure such exciting astrophysical phenomenon as gravitational redshifts from single, main sequence stars and extrasolar planets of terrestrial mass.

scholarly journals Signal-to-Noise Ratio and Astronomical Fourier Transform Spectroscopy

1988 ◽  
Vol 132 ◽  
pp. 71-78
Author(s):  
J. P. Maillard
Keyword(s):  
Fourier Transform ◽  
Signal To Noise Ratio ◽  
Resolving Power ◽  
High Resolution Spectroscopy ◽  
Signal To Noise ◽  
Array Detectors ◽  
Noise Ratio ◽  
The Fourier Transform ◽  
Large Telescopes ◽  
Very High

The multiplex properties of the Fourier Transform Spectrometer (FTS) can be considered as disadvantageous with modern detectors and large telescopes, the dominant noise source being no longer in most applications the detector noise. Nevertheless, a FTS offers a gain in information and other instrumental features remain: flexibility in choosing resolving power up to very high values, large throughput, essential in high–resolution spectroscopy with large telescopes, metrologic accuracy, automatic substraction of parasitic background. The signal–to–noise ratio in spectra can also be improved: by limiting the bandwidth with cold filters or even cold dispersers, by matching the instrument to low background foreoptics and high–image quality telescopes. The association with array detectors provides the solution for the FTS to regain its full multiplex advantage.

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