I will need to make a new release of MaTeX soon. If anyone has comments, complaints, suggestions to fix things in the package or its documentation, suggestions for cool documentation examples, etc. it would be a good time to let me know.

@Szabolcs I thought this was cool. AFAIK it has not been implemented, but I think it might be quite popular.

@C.E. I decided not to implement it because it is too easy to use it incorrectly and trigger errors (and Murphy's law tells us that I am going to get several support requests about it). But I also found it very cool, so I was planning to make MaTeX more extensible, and to show this as an extension example in the documentation. That's already 80% done.

@Szabolcs ok, sounds good.

It'll be in the release next week.

@Szabolcs I will be sure to check it out.

With ImageEffect "Decolorization" is there a hidden setting to control the starting white and ending black that is used for the range of colors. I want a softer decolorization so want to limit how dark it gets

@Edmund it's implemented by Image`ColorOperationsDump`iImageEffectDecolorization

Which is basically just OpenCVLink`Private`$Decolor

Which only takes one arg and is just decolor in OpenCV. So... no.

@b3m2a1 Thanks for the info.

@b3m2a1 I did find Colorize what appears to affect both the starting white and ending black with I use Lighter[GrayLevel@#, .5] & as the ColorFunction option. Still would like to control it separately.

Will see if there is another function

@Edmund What is your goal? ImageEffect[ ..., "Decolorization"] will take care to keep the contrast between parts of the image the same, whereas Lighter[GrayLevel@#, .5] will not. If you simply want to rescale the values to fit them into a certain interval then you can use ImageData and Rescale.

@C.E. I am using it for GeoStyling in the GeoStylingImageFunction option to make the GeoBackground grey scale for a GeoGraphics. I want it to be a "soft" gray scale (i.e. not go all the way to black) as this will complement the custom geo markers I have made to display the location information.

@C.E. ImageEffect[..., "Decolorization"] does produce a better effect except that some colours are black.

@Edmund Although it says "Contrast preserving decolorization", you should implement this transformation yourself. It is quite easy.

If you still want to use ImageEffect, why don't you apply a filter afterwards to lift the black colours to grey?

@halirutan Did not think of that. To be honest ImageEffect and Colorize are about the extend of my image colour processing knowledge at the moment.

@Edmund In its simplest form, you lift the black by changing the mapping of grays that run from 0 (black) to 1 (white):

Manipulate[
 Plot[Rescale[x, {0, 1}, {b, 1}], {x, 0, 1},
  PlotRange -> {{0, 1}, {0, 1}}],
 {b, 0, .5}
 ]

It should be clear that after that transformation, your image looks more "flat" because it only uses a smaller part of the gray-range.

So look at the transformation Rescale[x, {0, 1}, {b, 1}] and then you can do something like this:

img = ExampleData[{"TestImage", "Lena"}];

With[{gray = ImageEffect[img, "Decolorization"]},
 Manipulate[
  ImageApply[min + (1 - min) # &, gray],
  {min, 0, .5}
  ]
 ]