On Monday, November 16, 2015 02:25:43 AM Tobias Knopp wrote: > 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?
I'm not aware of a package that implements alpha-compositing. Perhaps it could be added to ColorVectorSpace (which might then need a new name), or perhaps better it could be its own package. If you're interested in this, I'd recommend starting by creating a type that makes it clear whether you're working with pre-multiplied alpha or not, see https://en.wikipedia.org/wiki/Alpha_compositing#Description > - 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 ImageCmap lets you define a colormap that includes an alpha channel, but it doesn't implement any special operations. > > - The third is: given a colormap, how to interpolate into it (+ window > level, window brightness). Not quite sure what you mean, are you asking if you can have a fractional value that lies between two points in the colormap? If the operations you want to implement can be expressed in terms of + and * via the standard rules of interpolation, this one should be easy :-): just use Interpolations.jl to create the colormap vector, e.g., icmap = interpolate(cmap, BSpline(Linear())) and pass that to ImageCmap. We can easily generalize it to allow an AbstractVector. Note that currently img[i,j] for an ImageCmap returns the index, not the color value. I don't remember why I did it that way, but I think that's something that will have to change. Just need to think of the right migration strategy. Best, --Tim > > 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/cac28026250814f6ae6594dd26e92707 > > 6177db60/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
