[vtkusers] Clarification and help using vtkLookupTable

[Neel Patel 0-0-0]

Hi All,

I'm trying to use vtkLookupTable to add color in my image, something
like what they show on the weather forecasts. From what I understand,
SetRange(0,255) means that any pixel value in the image that is in between
the min and max, will be assigned a value that has been set by
SetTableValue(0, 0, 0, 0, 0) and SetTableValue(255, 255, 255, 255, 1). To
test this out I made a simple lookupTable where everything except for 0 was
given a rgb value of 255, 0, 0;

vtkLookupTable table = vtkLookupTable.New();
table.SetRange(0, 255);
table.SetTableValue(0, 0, 0, 0, 0);

for (int i = 1; i < 255; i++)
{
table.SetTableValue(i, 255, 0, 0, 0.3);
}
table.SetRampToLinear();
table.Build();

This however still gives me and image with red, green, and blue showing up
instead of just red. Also just to note this is on top of a black/white
image, so there aren't any other places from which the colors could come
from. Any help would be appreciated. Thanks.

Regards,
Neel Patel





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[David E DeMarle]

Take out the calls to set ramp and especially build. Build replaces all of
the value:colors you've set with automatically generated ones.

Post by Neel Patel 0-0-0
Hi All,
I'm trying to use vtkLookupTable to add color in my image, something
like what they show on the weather forecasts. From what I understand,
SetRange(0,255) means that any pixel value in the image that is in between
the min and max, will be assigned a value that has been set by
SetTableValue(0, 0, 0, 0, 0) and SetTableValue(255, 255, 255, 255, 1). To
test this out I made a simple lookupTable where everything except for 0 was
given a rgb value of 255, 0, 0;
vtkLookupTable table = vtkLookupTable.New();
table.SetRange(0, 255);
table.SetTableValue(0, 0, 0, 0, 0);
for (int i = 1; i < 255; i++)
{
table.SetTableValue(i, 255, 0, 0, 0.3);
}
table.SetRampToLinear();
table.Build();
This however still gives me and image with red, green, and blue showing up
instead of just red. Also just to note this is on top of a black/white
image, so there aren't any other places from which the colors could come
from. Any help would be appreciated. Thanks.
Regards,
Neel Patel
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[Neel Patel 0-0-0]

Got it. I assumed that build created the table with all the set values.
Thanks David!



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[Franks]

Dear Mr. Patel
I have the same problem as you. I saw your problem, but still don't
understand why it works like that. Could you do me a favour to have a look
and tell me your understanding about *SetRange()*.
Thank you, and I look forward to hearing from you.
Best regards,
Franks



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[Franks]

I have the same problem as Neel. I read your answer, but still don't
understand why it works like that. Could you do me a favour to have a look
and tell me what does *SetRange()* work.
Thank you, and I look forward to hearing from you.
Best regards,
Frank

Post by David E DeMarle
Take out the calls to set ramp and especially build. Build replaces all of
the value:colors you've set with automatically generated ones.
On Aug 7, 2017 8:04 PM, "Neel Patel 0-0-0" &lt;

Post by Neel Patel 0-0-0
Hi All,
I'm trying to use vtkLookupTable to add color in my image, something
like what they show on the weather forecasts. From what I understand,
SetRange(0,255) means that any pixel value in the image that is in between
the min and max, will be assigned a value that has been set by
SetTableValue(0, 0, 0, 0, 0) and SetTableValue(255, 255, 255, 255, 1). To
test this out I made a simple lookupTable where everything except for 0 was
given a rgb value of 255, 0, 0;
vtkLookupTable table = vtkLookupTable.New();
table.SetRange(0, 255);
table.SetTableValue(0, 0, 0, 0, 0);
for (int i = 1; i < 255; i++)
{
table.SetTableValue(i, 255, 0, 0, 0.3);
}
table.SetRampToLinear();
table.Build();
This however still gives me and image with red, green, and blue showing up
instead of just red. Also just to note this is on top of a black/white
image, so there aren't any other places from which the colors could come
from. Any help would be appreciated. Thanks.
Regards,
Neel Patel
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[Andras Lasso]

Probably the most efficient way of learning exact behavior of simple classes is to read their source code.

vtkLookupTable is a really simple one and its source code is available here:
https://github.com/Kitware/VTK/blob/master/Common/Core/vtkLookupTable.cxx

Andras

-----Original Message-----
From: vtkusers <vtkusers-***@public.kitware.com> On Behalf Of Franks
Sent: Friday, November 2, 2018 11:29 PM
To: ***@vtk.org
Subject: Re: [vtkusers] Clarification and help using vtkLookupTable

I have the same problem as Neel. I read your answer, but still don't understand why it works like that. Could you do me a favour to have a look and tell me what does *SetRange()* work.
Thank you, and I look forward to hearing from you.
Best regards,
Frank

Post by David E DeMarle
Take out the calls to set ramp and especially build. Build replaces
all of the value:colors you've set with automatically generated ones.
On Aug 7, 2017 8:04 PM, "Neel Patel 0-0-0" &lt;

Post by Neel Patel 0-0-0
Hi All,
I'm trying to use vtkLookupTable to add color in my image,
something like what they show on the weather forecasts. From what I
understand,
SetRange(0,255) means that any pixel value in the image that is in
between the min and max, will be assigned a value that has been set
by SetTableValue(0, 0, 0, 0, 0) and SetTableValue(255, 255, 255, 255,
1). To test this out I made a simple lookupTable where everything
except for 0 was given a rgb value of 255, 0, 0;
vtkLookupTable table = vtkLookupTable.New();
table.SetRange(0, 255);
table.SetTableValue(0, 0, 0, 0, 0);
for (int i = 1; i < 255; i++)
{
table.SetTableValue(i, 255, 0, 0, 0.3);
}
table.SetRampToLinear();
table.Build();
This however still gives me and image with red, green, and blue
showing up instead of just red. Also just to note this is on top of a
black/white image, so there aren't any other places from which the
colors could come from. Any help would be appreciated. Thanks.
Regards,
Neel Patel
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