# Rwavelet Vignette

#### Christophe Chesneau and Fabien Navarro

#### 2026-08-28

# 1 1d examples

## 1.1 Load and plot a signal from the MakeSignal function

    J <- 10; n <- 2^J; t <- (1:n) / n
    name <- c('Bumps')
    f <- MakeSignal(name, n)
    plot(t, f, xlab="t", ylab="f(t)",
         type='l', lwd=1.2, main=name)

## 1.2 Plot a noisy version of the original function

    SNR <- 4
    set.seed(1)
    ssig <- sd(f)
    sigma <- ssig / SNR
    y <- f + rnorm(n, mean=0, sd=sigma)
    plot(t, y, xlab="t", ylab="y", main=paste("Noisy", name))

## 1.3 Forward Wavelet Transform (periodized, orthogonal)

    qmf <- MakeONFilter('Daubechies', 10)
    j0 <- 3
    wc <- FWT_PO(y, j0, qmf)
    wch <- wcs <- wcbs <- wcbh <- wc
    wcf <- FWT_PO(f, j0, qmf)

## 1.4 Spike-plot display of wavelet coefficients

    PlotWaveCoeff(wc, j0, 0.5)
    title("Noisy Wavelet Coefs")

    PlotWaveCoeff(wcf, j0, 0.5)
    title("Original Wavelet Coefs")

## 1.5 Universal hard thresholding

    # estimate sigma using the Median Absolute Deviation
    # using only the fine scale of wc
    hatsigma <- MAD(wc[(2^(J-1)+1):2^J])
    thr <- sqrt(2*log(length(y)))*hatsigma
    # apply hard thresholding
    wch[(2^(j0)+1):n] <- HardThresh(wc[(2^(j0)+1):n], thr)
    # plot the resulting coeficients estimates
    PlotWaveCoeff(wch, j0, 0.5)
    title("Estimated Wavelet Coefs")

    fest <- IWT_PO(wch, j0, qmf)
    snrout <- SNR(f, fest)
    plot(t, fest, type='l', lwd=1.4, col='red', xlab="t", ylab="hat_f(t)",
           main=format(round(snrout,2), nsmall=2))
    matlines(t, f, type='l', lty=2)

## 1.6 Universal hard thresholding (Block version)

    L <- 2 # block size
    wcbh <- BlockThresh(wc, j0, hatsigma, L, qmf, thresh = "hard")
    fest_bh <- IWT_PO(wcbh,j0,qmf)
    PlotWaveCoeff(wcbh, j0, 0.5)
    title("Estimated Wavelet Coefs")

    plot(t, fest_bh, type='l', lwd=1.4, col='red', xlab="t", ylab="hat_f(t)",
           main=format(round(SNR(f, fest_bh),2), nsmall=2))
    matlines(t, f, type='l', lty=2)

## 1.7 Universal soft thresholding

    wcs[(2^(j0)+1):n] <- SoftThresh(wc[(2^(j0)+1):n], thr)
    PlotWaveCoeff(wcs, j0, 0.5)
    title("Estimated Wavelet Coefs (soft)")

    f_soft <- IWT_PO(wcs, j0, qmf)
    plot(t, f_soft, type='l', lwd=1.4, col='red', xlab="t", ylab="hat_f(t)",
           main=format(round(SNR(f, f_soft),2), nsmall=2))
    matlines(t, f, type='l', lty=2)

## 1.8 Universal soft thresholding (Block version)

    wcbs <- BlockThresh(wc, j0, hatsigma, L, qmf, thresh = "soft")
    PlotWaveCoeff(wcbs, j0, 0.5)

    fest_bs <- IWT_PO(wcbs,j0,qmf)
    plot(t, fest_bs, type='l', lwd=1.4, col='red', xlab="t", ylab="hat_f(t)",
           main=format(round(SNR(f, fest_bs),2), nsmall=2))
    matlines(t, f, type='l', lty=2)

# 2 2d examples

## 2.1 Load and plot an image

    name <- '../inst/extdata/lena.png'
    if (requireNamespace("imager", quietly = TRUE)) {
          f <- imager::load.image(name)
          plot(f, axes=F, interpolate=F, xlab="", ylab="")
       } else {
          ## use e.g. image from graphics package
       }

## 2.2 Plot a noisy version of the original image

    ssig <- sd(f)
    sdnoise <- ssig/SNR
    y <- f + rnorm(ncol(f)*nrow(f), mean=0, sd=sdnoise)
    snrin <- SNR(f,y)
    if (requireNamespace("imager", quietly = TRUE)) {
          plot(y, axes=F, interpolate=F, xlab="", ylab="",
         main=format(round(snrin,2), nsmall = 2))
       } else {
          ## use e.g. image from graphics package
       }

## 2.3 Image denoising using hard thresholding

    wc <- FWT2_PO(as.array(imager::squeeze(y)), j0, qmf)
    wcb <- wc
    thr <- 3*sdnoise
    aT <- wc*(abs(wc)>thr)
    fest <- IWT2_PO(aT, j0, qmf)
    snrout <- SNR(f, fest)
    if (requireNamespace("imager", quietly = TRUE)) {
          plot(imager::as.cimg(fest), axes=FALSE, xlab="", ylab="",
         main=format(round(snrout,2), nsmall=2))
       } else {
          ## use e.g. image from graphics package
       }

# 3 3d example

## 3.1 Load and plot a 3d image

    library(misc3d)
    library(rgl)
    data("SLphantom")
    n <- dim(SLphantom)[1]
    contour3d(SLphantom,0)
    rglwidget()

    sig <- sd(SLphantom)
    sdnoise <- sig/SNR
    y <- SLphantom + rnorm(n^3, mean=0, sd=sdnoise)
    wcf <- FWT3_PO(SLphantom,j0,qmf)
    wc <- FWT3_PO(y,j0,qmf)
    wcn <- wc
    thr <- 3*sdnoise
    wc <- wc*(abs(wc)>thr)
    fhat <- IWT3_PO(wc, j0, qmf)

    op <- par(mfrow=c(3,3), mgp = c(1.2, 0.5, 0), tcl = -0.2,
    mar = .1 + c(0.1,0.1,0.1,0.1), oma = c(0,0,0,0))
    ll=screen=list(z = 130, x = -80)
    contour3d(SLphantom,0,color="gray", engine = "standard")
    contour3d(y,0.05,color="gray", engine = "standard")
    contour3d(fhat,0.2,color="gray", engine = "standard")
    contour3d(wcf,0.1, color="gray", engine = "standard")
    contour3d(wcn,0.05,color="gray", engine = "standard")
    contour3d(wc,0.1,color="gray", engine = "standard")
    plot(as.cimg(SLphantom[n/2,,]), axes=FALSE, xlab="", ylab="")
    plot(as.cimg(y[n/2,,]), axes=FALSE, xlab="", ylab="")
    plot(as.cimg(fhat[n/2,,]), axes=FALSE, xlab="", ylab="")