mta2:

#' Creates difference-heatmap of two trajectory heatmap images
#' 
#' \code{mt_diffmap} creates a difference-heatmap of the trajectory 
#'   data using gaussian smoothing. 
#' 
#' @param image1 a data frame containing the trajectory image created by 
#'   \code{mt_heatmap}. The first three columns are expected to be named "x", 
#'   "y", "img" and contain the respective information.
#' @param image2 see \code{image1}. Must match the dimensions of \code{image1}.
#' @param device a character specifying the plotting device. Either \code{tiff},
#'   \code{png}, or \code{pdf}. Defaults to \code{tiff}.
#' @param name a character string specifying the filename
#' @param directory a character string specifying the directory for the image 
#'   file. Defaults to \code{get.wd()}.
#' @param upscale a numeric by which the output resolution of the image is 
#'   increased or decreased. Only applies if \code{device} is one of 
#'   \code{c("tiff","png","pdf")}.
#' @param smooth_radius a numeric specifying the standard deviation of the 
#'   gaussian smoothing. If zero smoothing is omitted.
#' @param colors a character vector specifying the colors used to color
#'   cases where \code{image1 > image2, image1 ≈ image2, image1 < image2},
#'   respectively. Note that the colors will necessarily be used in that
#'   specific order. Defaults to c("#00863F","#FFFFFF","#FF1900") which
#'   specifies a green-white-red color gradient.
#' @param n_shades integer specifying the number of shades for the color 
#'   gradient between the first and second, and the second and third color in
#'   \code{colors}.
#' @param plot boolean specifying whether the image should be plotted. If
#'   \code{plot} is \code{FALSE}, then the image will be returned.

mt_diffmap = function(
  image1,
  image2,
  device = 'tiff',
  name = 'image',
  directory = getwd(),
  upscale = 1,
  smooth_radius = 0,
  colors   = c("#00863F","#FFFFFF","#FF1900"),
  n_shades = 10,
  plot = TRUE
  ){
  
  # get image
  if(!is.data.frame(image1)) image1 = image1[[1]]
  if(!is.data.frame(image2)) image2 = image2[[1]]
  
  # compute difference
  img = image1
  img$img = image1$img - image2$img
  
  # smooth image
  if(smooth_radius > 0) img$img = mta2:::gaussBlur(img$img,img$img,max(img$x),max(img$y),smooth_radius)

  # determine colors
  v   = img$img
  v   = v / max(abs(v))
  if(n_shades > 0){
    vp = v[v>0]
    vm = v[v<=0]
    vp = mousetrap:::group(vp,n_shades)
    vm = mousetrap:::group(vm,n_shades)  
    v[v>0]  = vp
    v[v<=0] = vm
    }

  col1 = mousetrap:::colormixer(colors[2],colors[1],abs(v),'hex')
  col2 = mousetrap:::colormixer(colors[2],colors[3],abs(v),'hex')  
  img$col    = ifelse(v > 0, col1, col2)
  img$img    = v
  
  # plot image
  if(plot == TRUE){
    
    if(device == 'pdf'){
      pdf(paste0(directory,'/',name,'.pdf'),
          width = 10 * (max(img$x)/max(img$y)) * upscale,
          height = 10 * upscale)
          }
    if(device == 'png'){
      tiff(paste0(directory,'/',name,'.png'),
           width = max(img$x) * upscale,
           height = max(img$y) * upscale)
           }
    if(device == 'tiff'){
      tiff(paste0(directory,'/',name,'.tiff'),
           width = max(img$x) * upscale,
           height = max(img$y) * upscale)
           }
    
    
    xs_range = range(img$x)
    ys_range = range(img$y)
    plot.new();par(mar=c(0,0,0,0));plot.window(xlim=xs_range+c(-.5,.5),
                                               ylim=ys_range+c(-.5,.5))
    
    # plot points
    rect(img$x - .5,img$y - .5,
         img$x + .5,img$y + .5, col=img$col,
         border=NA)
    
    }
  
  if(device %in% c('pdf','png','tiff') & plot == TRUE) dev.off()
  
  if(plot == FALSE) return(img)
  
  }