[vtkusers] Complementary color LUTs

[David Gobbi]

It looks like the "Window" part of your Window/Level setting is wrong.

On Wed, Apr 20, 2016 at 6:15 PM, Jothybasu Selvaraj <jothybasu at gmail.com>
wrote:

> Sorry, with the GreenTable->SetRampToLinear() it looks like the one in
> the attached figure. But I would like to visualize some anatomical details
> as in the previous Ref.jpg.
>
> Thanks
>
> Jothy
>
> On Thu, Apr 21, 2016 at 9:55 AM, Jothybasu Selvaraj <jothybasu at gmail.com>
> wrote:
>
>> Hi David
>>
>> Though it works, I would like to have the images rendered like the one
>> shown in Ref.jpg. With the current code it is rendered like the one in the
>> attached Current.jpg.
>>
>> Thanks
>>
>> Jothy
>>
>> On Thu, Apr 21, 2016 at 9:32 AM, Jothybasu Selvaraj <jothybasu at gmail.com>
>> wrote:
>>
>>> Fantastic David!
>>>
>>> With the latest modification on table2 you sent, it  works well.
>>>
>>> I agree, it will be great if VTK can add a class to do this where users
>>> can choose a set of colors they need to fuse.
>>>
>>>
>>> Thanks a lot!
>>>
>>>
>>> Cheers
>>>
>>> Jothy
>>>
>>> On Thu, Apr 21, 2016 at 12:45 AM, David Gobbi <david.gobbi at gmail.com>
>>> wrote:
>>>
>>>> Looks like I was wrong about the second table.  It should use this:
>>>>
>>>>     table2 ->SetValueRange(0.0,1.0);
>>>>     table2 ->SetAlphaRange(0.5,0.5);
>>>>
>>>> Ideally, it would be nice if VTK provided a way to simply add the
>>>> two colors together, but the best you can do is use the alpha to
>>>> make VTK multiply the images by 0.5 before adding them.  As a
>>>> result, you end up with grey instead of white.
>>>>
>>>>  - David
>>>>
>>>> On Wed, Apr 20, 2016 at 1:15 AM, David Gobbi <david.gobbi at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi Jothy,
>>>>>
>>>>> I see this mistake a lot... people try to blend images by setting the
>>>>> alpha of both images to 0.5.  That's wrong.  If you want to blend images,
>>>>> then the first image should be opaque, and the second image should have an
>>>>> alpha of 0.5.
>>>>>
>>>>> C = C1*(1 - alpha2) + C2*alpha2
>>>>>
>>>>> The second mistake is that, if you want to blend complimentary colors,
>>>>> then you don't want the Value of the second image to be the ramp.  Instead,
>>>>> you want the Alpha of the second image to be the ramp.
>>>>>
>>>>>     // Create a GREEN lookup table
>>>>>     vtkSmartPointer<vtkLookupTable> table =
>>>>>             vtkSmartPointer<vtkLookupTable>::New();
>>>>>     table->SetHueRange(0.33333,0.33333);
>>>>>     table->SetSaturationRange(1.0,1.0);
>>>>>     table->SetValueRange(0.0,1.0);
>>>>>     table->SetAlphaRange(1.0,1.0); // make the bottom image opaque
>>>>>     table->SetRampToLinear();
>>>>>     table->Build();
>>>>>
>>>>>     // Create a MAGENTA lookup table
>>>>>     vtkSmartPointer<vtkLookupTable>table2 =
>>>>>             vtkSmartPointer<vtkLookupTable>::New();
>>>>>     table2 ->SetHueRange(0.8333,0.8333);
>>>>>     table2 ->SetSaturationRange(1.0,1.0);
>>>>>     table2 ->SetValueRange(1.0,1.0); // use pure magenta, don't mix
>>>>> with black
>>>>>     table2 ->SetAlphaRange(0.0,1.0); // use an alpha ramp to blend the
>>>>> images
>>>>>     table2 ->SetRampToLinear();
>>>>>     table2 ->Build();
>>>>>
>>>>> - David
>>>>>
>>>>>
>>>>> On Tue, Apr 19, 2016 at 11:43 PM, Jothybasu Selvaraj <
>>>>> jothybasu at gmail.com> wrote:
>>>>>
>>>>>> Hi All
>>>>>>
>>>>>> I am trying to overlay 2 registered images using complementary LUTs
>>>>>> (magenta & green), so that the images will appear white where they match
>>>>>> perfectly. However, I couldn't get the desired results. The image appears
>>>>>> magenta where they match.
>>>>>>
>>>>>> Can anyone find any mistakes in this?
>>>>>>
>>>>>> Below are the LUTs I use:
>>>>>>
>>>>>> // Create a GREEN lookup table
>>>>>>
>>>>>>     vtkSmartPointer<vtkLookupTable> table =
>>>>>>
>>>>>>             vtkSmartPointer<vtkLookupTable>::New();
>>>>>>
>>>>>>     table->SetHueRange(0.33333,0.33333);
>>>>>>
>>>>>>     table->SetSaturationRange(1.0,1.0);
>>>>>>
>>>>>>     table->SetValueRange(0.0,1.0);
>>>>>>
>>>>>>     table->SetAlpha(0.5);
>>>>>>
>>>>>>     table->SetRampToLinear();
>>>>>>
>>>>>>     table->Build();
>>>>>>
>>>>>>
>>>>>> // Create a MAGENTA lookup table
>>>>>>
>>>>>>     vtkSmartPointer<vtkLookupTable>table2 =
>>>>>>
>>>>>>             vtkSmartPointer<vtkLookupTable>::New();
>>>>>>
>>>>>>     table2 ->SetHueRange(0.8333,0.8333);
>>>>>>
>>>>>>     table2 ->SetSaturationRange(1.0,1.0);
>>>>>>
>>>>>>     table2 ->SetValueRange(0.0,1.0);
>>>>>>
>>>>>>     table2 ->SetAlpha(0.5);
>>>>>>
>>>>>>     table2 ->SetRampToLinear();
>>>>>>
>>>>>>     table2 ->Build();
>>>>>>
>>>>>>
>>>>>> Any help is highly appreciated!
>>>>>>
>>>>>>
>>>>>>
>>>>>> Cheers
>>>>>>
>>>>>>
>>>>>> Jothy
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>
>>
>
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