Attribute From Map

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Attribute From Map

Samples texture map information and stores it to a point attribute

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Summary:

    The attribute from map node is great because it allows you to use texture map information as the basis for a stored point attribute. The the main downside to this method is that you'll need to rely on UVs to apply the image along with a large amount of points on your mesh in order to properly capture the detail within the texture map.

    This method is not the same as applying applying a texture inside your shader and capturing the detail based on UV coordinates. This simply stores information on your points and the areas in-between those points are linearly interpolated.
Keep in mind that if your mesh does not have UVs, then a default Orthographic map will be applied to the mesh.

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Main Parameters:


Point Group:

--  If you want to only affect certain points on your mesh with this node, then those point ids can be specified here.

Texture Map:

--  When enabled, specifies the image or image sequence to sample the color information from. If disabled, the default Cd (point color value) is used.  If you would like to use a sequence of images, you can utilize the $F variables to substitute frame numbers inside the string.

UDIM Filename Expansion: 

-  If you are using UDIM tiling, then you'll want to check this on.  It tells Houdini that's it's cool to use the expression:
 %(UDIM)d
When substituting for the 1001 1002 1003... etc... in your UDIM texture file name.  If you want to explore other expressions that Houdini understands when it comes to UDIMs, visit this link: 
 https://www.sidefx.com/docs/houdini/vex/functions/expand_udim.html

Texture Channel:

-  If you are using an .exr file format, you can specify which channel you would like to use here.  As an example, lets say that the alpha (The "A" in RGBA) on an image is stored as its own channel within the exr.  With this parameter, you can tell Houdini to load in that particular channel instead of RGB.

UV Attribute:  

-  Specifies which set of UV coordinates you'd like to use.  99% of the time, you'll want to keep this at the default of uv.  If you have different uv sets on something, however, then you can type the name of that other uv set here.

Export Attribute: 

-  Specifies what sort of attribute you want to apply to your points.  Don't forget that a "Vector" means a set of three values (such as color: "RGB" as an example) or "Float" which means just one value that's allowed to have a decimal value. (such as using a black and white image to get values between 0 - black and 1 - white)

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Color Settings:

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It's important to note this:  If you are applying a float attribute to your points, then the grayed out parameters in the color settings will become active because it relates to how the float attribute is created.
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Source Color Space:

--  This refers to the gamma correction which is applied to the image.  In most situations, you'll want to leave this at automatic.  If you are sourcing in an sRGB image (8 or 16 bit) then it will apply a 2.2 gamma curve reduction to read off the appropriate values which visually correspond to what you're expecting.  For more information on color correction, gamma, and the like, be sure to visit the Color Management course for more information.

Color Channel:

--  When sampling to a float, Color Channel selects what color (or combination of colors) to sample. Greyscale is the default and creates a greyscale representation of the image to store as an attribute. 

If you don't know yet - images feature multiple channels which come together to form the image. (R for red, G for green, and B for blue).  Because float values create one decimal value rather than a set of three values, this color channel is asking you how you would like to read the channel information (which, again is a series of three values - R,G,B) and turn it into a float.  Do you want to just read the red channel?  The green?  Do you want to take the combination of all three channels and do that?  This is where you specify that information.

Color Influence:

--  Let's say that you want the red channel to influence the brightness of the resulting float/grayscale value.  Well, you can do that right here with the color influence.  In most situations I'd recommend setting this to 1,1,1,0 so that you basically just see a grayscale version of your colored image.

Visualize:

--  Let's say that you want to apply an attribute to your mesh that is NOT color (Cd).  But, you want to still visually see what those values are in your viewport.  This is what the visualize toggle will do.  It will create a Cd attribute that overrides any other Cd attribute that may be present on the mesh so that you can see what you're doing.  Turn this checkbox off once you're done with it.

Do Remap:

--  Want to change the resulting values without re-exporting a new texture map?  That's what you can do here.

Scale:

--  Brighten or darken everything in general

Contrast:

--  Make your darker values closer to 0 and your brighter values closer towards 1.

Contrast Rolloff:

--  Want to only affect values that are closer towards 0.5 with your contrast setting above?  This will let you do that.  A value of 1 means that the contrast effect stretches all the way between 0 and 1, and a lower value brings the effect closer towards 0.5

Remap Influence:

--  Look at the left-hand side of the ramp.  That's where the value of 0 (black) gets placed from your texture map.  Now look at the right.  That's where 1 (white) gets placed.  If you click in-between those two sides, you can alter the in-between values by adjusting the ramp.

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Filter Settings:

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This section deals with image filtering:  If you've never learned about this topic visit this video for a quick overview:  https://youtu.be/hqi0114mwtY?t=24

Also, this deals with the edges of your texture map (that is, if your texture map repeats, streaks, or does nothing if it's scaled down)

In 99% of situations, you won't need to adjust anything here unless you're trying to utilize a repeating texture map.
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Filter: 

--  Specifies which algorithm to use when filtering the edges of objects in your image.  To learn more about different types of filters, visit this link:

https://help.graphisoft.com/AC/18/INT/AC18Help/Appendix_Settings/Appendix_Settings-155.htm

Filter Width:

--  See Above

Wrap:

-  What will the image do when the scale doesn't fit into 0 to 1 uv space?  Will it Repeat itself?  Will it Streak as if the border pixel values are extended to infinity?  Or will it be a Decal.  The decal means that the image is surrounded by a solid color.  This color can be specified by the border color parameter.  Truth be told, I've never gotten "decal" to work.

Vertex UV Promotion:

-  Lets say that you have a point which is shared between two vertices.  These two vertices are being used to draw out two different polygon primitives, and both vertices belong to different UV sets.  Which UV attribute will the point listen to when it goes to sample the value?  This parameter will determine how the point reads information from those two vertices which share a point.

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Image Settings:

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This section allows you to change the transformation of the image as it's being placed in uv space.  These parameters are only relevant when using repeatable textures, and their controls are fairly self-explanatory.  Just remember that U = the horizontal direction in UV space and V = the vertical direction.
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