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Project Description

Ron would like to see a scalable architecture for the visual appearance of Slicer viewers as we add more types of elements and more of them. This architecture will also need to be able to accommodate new types of viewers such as graphs and tables.

We would also like to prepare a guide for developers of new types of viewers:

  • that ensures that all viewers have a consistent visual and interaction design,
  • and that makes it simpler for a developer to implement their viewer.

Slicer Reserved Colors and Viewer Colors Registry

Draft palette for viewer colors

Draft palette for viewer colors against which developers register

Draft Palette

Color Name Use Developer(s) HEX RGB
White Indicates active slice/frame in a multi-slice/frame viewer. Core #ffffff 255 255 255
Grey Generic Slice Viewers Core #8c8c8c 140 140 140
Grey1 Unused None #a8aac2 168 170 194
Grey2 Unused None #787b93 120 123 147
Grey3 Unused None #5b5e71 91 94 113
Grey4 Unused None #434450 67 68 80
Black 3D Viewer Background & Default Widget Text Core #000000 0 0 0
Yellow Saggital Slice Viewer Core #e6cf49 230 207 73
Cream Unused None #faf8dd 250 248 221
Wheat Unused None #ded6a5 222 214 165
Buff Yellow Unused None #d5d86f 213 216 111
Yellow Ochre Unused None #c19a1c 193 154 28
Camel Unused None #765d10 118 93 16
Red Axial Slice Viewer Core #ef4832 239 72 50
Light Red Unused None #d5a6a5 213 166 165
Magenta Unused None #954473 149 68 115
Rose Unused None #9f5668 159 86 104
Brick Unused None #703543 112 53 67
Burgundy Unused None #7f2430 127 36 48
Green Coronal Slice Viewer Core #6cad49 108 173 73
Soft Green Unused None #91ae6f 145 174 111
Moss Green Unused None #898e26 137 142 38
Cool Green Unused None #81cf9f 129 207 159
Summer Green Unused None #3d7b5d 61 123 93
Dark Green Unused None #455535 69 85 53
Blue 3D Viewers Core #707ee2 112 126 226
Slicer Blue Default background on 3D Viewers Core #a2a0e0 162 160 224
Steel Blue Unused None #d3d4f9 211 212 249
Slate Blue Unused None #6b8b93 107 139 147
Water Blue Unused None #327dbc 50 125 188
Turquoise Unused None #3b6a81 59 106 129
Dark Blue Unused None #3b4a71 59 74 113
Lilac Unused None #e3cfe9 227 207 233
Lavender Unused None #b095bb 176 149 187
Cool Purple Unused None #6b629c 107 98 156
Violet Unused None #6e4b7c 110 75 124
Dark Violet Unused None #4a3b54 74 59 84
Orange Compare Viewers Core #de6e11 222 110 17
Peach Unused None #ffd59f 255 213 159
Light Orange Unused None #eba965 235 169 101
Rust Unused None #aa4b1a 170 75 26
Clay Brown Unused None #a16643 161 102 67
Dark Brown Unused None #5b4c37 91 76 55

useful references

Notebook for Slicer 4 Presentation Layer Design

Notes & Sketches (Chronologically listed)

On Color-coding viewers & Qt Colors

Slicer default appearance as of 7-32: Slim-line color bars with sliders and pop up
  • (from Jim) Many of the viewers we are using colors from the Qt palette. The viewer "name" is color alias that is recognized by Qt. But it doesn't need to be this way. We could always go through a lookup to map viewers with nonstandard color names as the viewer name to a RGB triple. We'll just need to slip in that mapping in the appropriate places. Qt accepts "named colors" from the SVG color keywords. See Qt can also take ANY color specified as RGB, HSV, etc. components.
    • Views (layouts) associated with SliceNodes have an attribute in their XML description for "viewcolor". This allows the name of the view to be decoupled from the color of the view. "viewcolor" is typically specified as a "#RRGGBB" string.
  • (from Julien) There are 2 kinds of palettes:
    • a general "Qt application GUI" palette (color of the background, buttons, text, shadings, highlight color). This is QPalette.
    • a Slicer/MRML specific palette: color of the slice views, renderer background color of the 3D view, highlight of current view (slice or 3D). For now there is no placeholder for such a palette. I somewhat started to gather them in qMRMLColors.h/cxx. However, I believe it should be a VTK/MRML palette. Where MRML could provide a default palette, that can be extended/replaced by a Slicer palette.
  • (from Julien) I've noticed there has been some work done in the past to allow such kind of feature: Slicer4\Modules\Meshing\BuildingBlock\vtkSlicerColor.h/cxx. I'm not sure in what extend we could reuse/generalize that work. For information, vtkMRMLViewNode already hardcodes the light blue background color.
  • (question from Julien) Shall we make such a palette a singleton in MRML, or should it be a vtkMRMLScene member, other ideas ?
  • (from Jim) The colors for the various viewers feels more like "application settings" or "look and feel" than MRML. I don't feel strongly about this but I wonder if the colors just need to be accessible from the Application object. I guess since we store things like the layout in MRML, it would make sense for the available colors to decorate the UI also be established in MRML.

  • (from Wen) A first suggestion for how to color-code and ID viewers -- straw man for discussion:
Mock-up from 8/02: Viewer type color coding and ID (need to revise this with new roll-over color bar)
    • Keep Slicer Axi/Sag/Cor color coding, and all other individual slice viewers are grey
    • Keep Compare Viewers Orange
    • Make 3D viewers blue (better shade than in mockup!)
    • darken down the hairline frame around all viewers so "active" viewer is more apparent.
    • Multiple viewers of same viewer-type get a numerical ID
    • Create list of colors that developers register new viewer types to...
    • Helper code to create a viewer frame with same appearance & behavior
Mock-up from 8/02: Active Viewer Color = White for all viewer types (need to revise this with new roll-over color bar)
    • Question: Will we have more than one active viewer?
      • what would be a use case scenario?
      • what does active mean?
Mock-up from 8/02: Active Viewer Color = White for all viewer types (need to revise this with new roll-over color bar)

    • Lighten display up: if GUI panels are collapsed by default, and only expose on rollover, then we don't need to tie the image viewer to the color bar with a hairline of the same color. We can just use a just-noticeable grey divider which turns white on highlight. This may clean up the overall appearance a bit.
Mock-up from 8/02: Cleaner viewer appearance (need to revise this with new roll-over color bar)

    • Mockup with new rollover design. Larger area for rollover activation of controls and clicking to pin them open (easier to hit a larger target.) Gap between the hot area and the slice scroller to minimize mistakes. Slice numbers always visible and editable. Active window shown with a symbol and white outline.
Mock-up from 8/12. Cleaner viewer appearance and modified interaction -- for discussion.

    • Mockup with extra gap to minimize inter-viewer clicking mistakes.
Mock-up from 8/12 incorporating Ron's comments. Minimizing selection errors among viewers.

    • Mockup with link status displayed AND with recenter button exposed on 3D viewers as per Ron's suggestion. Suggestion to make controls hug the widget boundary on right viewer side (if controls exceed some minimum width requirement) to make it clearer that they belong to a viewer, rather than that they are an independent window full of widgets...
Mock-up from 8/15 incorporating Ron's comments. Expose link status and control to re-center 3D views. Non-orange highlights on compare view. (Does this require more problem-solving?)

Slice Controller scetches

Link to sketches for controllers

Summary from tcon discussion 8/2/2011: Three types of "colors" in Slicer4

1. Qt application "skin" which can be selected through an Application Settings interface. This includes background, buttons, text, shadings etc.

  • This is implemented as a QPalette.

2. Slicer reserved colors that should-not be adjusted by the user.

  • Colors of the roll-over bar on specific viewer types (Slice Red, Yellow, Green for example) should not change. This permits all Slicer users to discuss presentation of data in a consistent way, independent of how Slicer's presentation layer is styled.

3. MRML-specific colors that are restored with the scene. This includes 3D view background color, Fiducial color, etc.

  • The set of color options are currently being collected in qMRMLColors.h/cxx.


  • A question remains on which category color-styling of vtk widgets falls under (e.g. colors of widget handles and highlights). Importantly, widget handle and highlight colors form a visual language that a user understands (grab here, this grabbed guy is active, etc.) Changing these color codes is effectively breaking the rules of that language. A user has to experiment to verify that they understand the interactive behavior of the widget. For this reason, wjp recommends we categorize widget handle colors as color type "2" above -- Slicer-reserved that are not adjustable.
    • being able to change the color of a fiducial is important. E.g. I have two fiducial lists and I would like to make one bone colored and one vein colored. Is the color of the fiducial a handle?
  • How to implement Color type 2 -- also as part of qMRMLColors.h/cxx?


Alternative appropriate skins should be exposed as options under an Application Settings Interface. Skins that are tailored to different use cases (radiology reading room, or in the OR e.g.) are of interest. Skins may or may not be specified in the MRML scene, but if a scene is loaded, a user's skin should not change automatically -- maybe a viewer is prompted for whether they want to switch to the application interface appearance described in the scene file, or whether they want to preserve their own.

Julien has sent Wen instructions for how to create skins in Qt.

Guidelines for Developers of New Viewers