Revisions to Composition: how to make a day and night world map?

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edited Jul 26, 2015 at 7:38

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Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageComposeImageCompose with the generated alpha channels (SetAlphaChannelSetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind the Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind the Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

deleted 27 characters in body

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edited Oct 3, 2012 at 13:39

J. M.'s missing motivation ♦

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581

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

added 537 characters in body

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edited Mar 28, 2012 at 3:28

Yu-Sung Chang

7.1k
1
39
31

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

enter image description here

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

Hope this helps.The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

enter image description here

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

Hope this helps.

Yes, the basic idea is here: Demonstration: Day and Night World Clock

Now, to use the images, create an alpha channel using the computed the day-night curve--called "terminator" curve (rasterize it in grayscale), and compose two images using ImageCompose with the generated alpha channels (SetAlphaChannel to the second image).

Try the following code:

a = Image[ConstantArray[{255, 0, 0}, {200, 300}]];
b = Image[ConstantArray[{0, 255, 0}, {200, 300}]];

(* This is just a made-up mask. Don't mind Plot[] part *)
mask = Rasterize[
  Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding->0,
    Filling->-1, FillingStyle->Black, Frame->False, 
    Axes->False, ImageSize->{300, 200}, AspectRatio->2/3],
  "Image", ColorSpace->"GrayScale"];

ImageCompose[a, SetAlphaChannel[b, mask]]

You should get an image with green and red mixed as below. Now you can replace a and b with your day and night textures.

I have to tell you that although the code there computes pretty close approximation of the actual terminator curve, it is not exact. To compute it accurately (or based on actual data), see: NOAA: Day Night Terminator

The following code and output is for the actual images (again the mask is fake):

day = ImageResize[day, {2048, 1024}]; (* Match the dimensions *)

mask = Rasterize[
   Plot[Sin[x], {x, -Pi/2, 3 Pi/2}, PlotRangePadding -> 0, 
    Filling -> -1, FillingStyle -> Black, Frame -> False, 
    Axes -> False, ImageSize -> {2048, 1024}, 
    AspectRatio -> 1024/2048], "Image", ColorSpace -> "GrayScale"];

ImageCompose[night, SetAlphaChannel[day, mask]]

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edited Mar 22, 2012 at 14:10

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edited Mar 22, 2012 at 7:19

Yu-Sung Chang

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edited Mar 22, 2012 at 7:10

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edited Mar 22, 2012 at 7:03

Yu-Sung Chang

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created Mar 22, 2012 at 6:51

Yu-Sung Chang

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