After investigating this a little further I found that the key things I am/was missing are: - How to compose two RGBA values a and b. It turns out that this is the "over" operation given by
c = alpha*b + (1-alpha)*a if alpha is the alpha channel of b and a has alpha=1. Do I have missed it or is the over operation somewhere implemented in a package? - The second thing is colormaps that include an alpha channel. This allows to overlay data in a very flexible way. Otherwise its not really clear how to compose things - The third is: given a colormap, how to interpolate into it (+ window level, window brightness). Cheers, Tobias Am Donnerstag, 12. November 2015 21:54:18 UTC+1 schrieb Tim Holy: > > On Thursday, November 12, 2015 12:15:46 PM Tobias Knopp wrote: > > Thanks Tim, I tried to look into the code of Overlay but it wasn't to > clear > > to me. In particular I am missing where the RGB(A) data is combined. > > Here: > > https://github.com/timholy/Images.jl/blob/cac28026250814f6ae6594dd26e927076177db60/src/overlays.jl#L60-L67 > > > > Is it > > really as simple as adding the individual RGB values and preventing > > overflow by clamp? > > Yes. > > > Or is there some infrastructure for color mixing in Colors.jl > > There is, but it's considerably slower. See the ColorVectorSpace.jl README > for > discussion. > > > I further looked for functions for gray value mapping > (Contrast/Brightness) > > in Colors.jl but could not find anything. This is of course not > complicated > > to code but I don't want to miss an existing solution. > > The whole "MapInfo" structure is a very flexible and powerful. Search for > it on > this page: > http://timholy.github.io/Images.jl/function_reference.html > From my standpoint, the best feature is that it's "lazy": you specify the > transformation you want, but don't execute it until you need it. For > people > like me who routinely browse 1TB images but probably look at <1% of the > raw > data in any given dataset (and who also don't have 1TB worth of RAM...), > this > is quite an advantage. > > In my own work, I pretty routinely design custom MapInfo types/map > functions > for visualization purposes. For example, I can color individual blobs in > each > frame of a movie with something along the lines of > > immutable ColorizeBlobs > blobpixels::Vector # of length nblobs > blobcolors::Vector{RGB{U8}} # color assigned to each blob > end > > and passing that to ImageView using the "scalei" keyword argument (a > legacy of > the days when this was called ScaleInfo rather than MapInfo). It's a nice > way > of getting custom visualization while leaving all the stupid zoom & > navigation > functionality up to ImageView. > > --Tim > > > > > Tobi > > > > Am Donnerstag, 12. November 2015 16:42:00 UTC+1 schrieb Tim Holy: > > > Probably the easiest thing would be to just extend the code in Images > and > > > submit a PR (the code is not very complicated). > > > > > > However, you can do very fancy things with MapInfo objects. This is > > > untested, > > > but it should be close: > > > > > > immutable TwoColormap <: MapInfo > > > > > > colormap1 > > > colormap2 > > > > > > end > > > > > > function map!(dest, mapi::TwoColormap, > > > src::Tuple{AbstractArray,AbstractArray}) > > > > > > img1, img2 = src > > > for I in eachindex(dest) > > > > > > dest[I] = clamp(RGBmapi.colormap1[img1[I]] + > > > > > > mapi.colormap2[img2[I]]) > > > > > > end > > > dest > > > > > > end > > > > > > --Tim > > > > > > On Thursday, November 12, 2015 07:23:07 AM Tobias Knopp wrote: > > > > Hi, > > > > > > > > I am using the OverlayImage type from the Images.jl package to > overlay > > > > > > two > > > > > > > different grayscale images (tomographic data). > > > > If I understand it correctly OverlayImage is restricted to colormaps > > > > > > that > > > > > > > go from black to a certain RGB value. Has anybody an idea how this > could > > > > > > be > > > > > > > extended to Colormaps provided by Colors.jl? > > > > > > > > So my need is: > > > > Input: two 3D datasets (FloatingPoint) + two Colormaps + WindowWidth > > > > WindowLevel for each > > > > Output: Combined 3D dataset as RGBA values. > > > > > > > > Thanks > > > > > > > > Tobias > >
