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v4.2.0: Add GetChannel/ChannelCount API for ergonomic channel access
ImageHDU and ImageData now expose: - ChannelCount: number of channels (1 for 2D, N for 3D+) - GetChannel(int index): returns a single channel as a rectangular array (e.g. float[,]), works for both 2D and 3D+ images Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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‎CSharpFITS/CSharpFITS.csproj‎

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<LangVersion>9.0</LangVersion>
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<PackageReadmeFile>README.md</PackageReadmeFile>
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<PackageLicenseFile>license.txt</PackageLicenseFile>
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<AssemblyVersion>4.1.0.0</AssemblyVersion>
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<FileVersion>4.1.0.0</FileVersion>
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<AssemblyVersion>4.2.0.0</AssemblyVersion>
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<FileVersion>4.2.0.0</FileVersion>
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<PackageTags>Astronomy,FITS,Image</PackageTags>
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<RepositoryUrl>https://github.com/SharpAstro/FITS.Lib</RepositoryUrl>
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<PackageProjectUrl>https://github.com/SharpAstro/FITS.Lib</PackageProjectUrl>
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<Description>Supports reading and writing FITS files</Description>
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<Version>4.1.0</Version>
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<Version>4.2.0</Version>
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<Authors>Virtual Observatory - India</Authors>
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<PackageId>FITS.Lib</PackageId>
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<RootNamespace>nom.tam</RootNamespace>

‎CSharpFITS/fits/ImageData.cs‎

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/// </summary>
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public virtual ImageTiler Tiler => tiler;
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/// <summary>The number of channels (planes) in the image.
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/// For 2D images this is 1. For 3D images this is the size of the first axis (NAXIS3).</summary>
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public int ChannelCount
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{
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get
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{
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var data = DataArray;
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if (data == null) return 0;
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int[] dims = ArrayFuncs.GetDimensions(data);
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return dims.Length <= 2 ? 1 : dims[0];
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}
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}
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/// <summary>Get a single channel (plane) of image data as a rectangular array.
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/// For 2D images, index must be 0 and returns the full image.
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/// For 3D images, returns the Nth channel as a rectangular 2D array.
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/// </summary>
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/// <param name="index">The zero-based channel index.</param>
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/// <returns>A rectangular array (e.g. float[,]) for the requested channel.</returns>
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/// <exception cref="IndexOutOfRangeException">If the index is out of range.</exception>
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/// <exception cref="InvalidOperationException">If image data is not available.</exception>
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public Array GetChannel(int index)
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{
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var data = DataArray;
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if (data == null)
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throw new InvalidOperationException("Image data is not available.");
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if (data is Array outerArray && ArrayFuncs.IsArrayOfArrays(data))
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{
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// 3D+ hybrid: jagged outer array of rectangular inner arrays
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if (index < 0 || index >= outerArray.Length)
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throw new IndexOutOfRangeException(
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$"Channel index {index} is out of range [0, {outerArray.Length}).");
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return (Array)outerArray.GetValue(index);
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}
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// 2D rectangular or 1D array
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if (index != 0)
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throw new IndexOutOfRangeException(
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$"Channel index {index} is out of range for a {ArrayFuncs.CountDimensions(data)}D image.");
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return (Array)data;
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}
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/// <summary>The size of the data
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/// </summary>
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internal long byteSize;

‎CSharpFITS/fits/ImageHDU.cs‎

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namespace nom.tam.fits
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namespace nom.tam.fits
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{
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/*
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* Copyright: Thomas McGlynn 1997-2007.
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* Many thanks to David Glowacki (U. Wisconsin) for substantial
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* improvements, enhancements and bug fixes.
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* The CSharpFITS package is a C# port of Tom McGlynn's
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* nom.tam.fits Java package, initially ported by Samuel Carliles
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*
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* Copyright: 2007 Virtual Observatory - India.
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*
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* Use is subject to license terms
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/*
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* Copyright: Thomas McGlynn 1997-2007.
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* Many thanks to David Glowacki (U. Wisconsin) for substantial
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* improvements, enhancements and bug fixes.
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* The CSharpFITS package is a C# port of Tom McGlynn's
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* nom.tam.fits Java package, initially ported by Samuel Carliles
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*
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* Copyright: 2007 Virtual Observatory - India.
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*
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* Use is subject to license terms
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*/
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using System;
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using util;
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using image;
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/// <summary>FITS image header/data unit.The ImageTiler class allows
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/// users to extract subimages from a FITS primary image or image extension.</summary>
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using image;
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/// <summary>FITS image header/data unit.The ImageTiler class allows
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/// users to extract subimages from a FITS primary image or image extension.</summary>
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public class ImageHDU : BasicHDU
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{
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{
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/// <summary>Indicate that Images can appear at the beginning of a FITS dataset</summary>
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internal override bool CanBePrimary => true;
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/// <summary>Change the Image from/to primary</summary>
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/// <summary>Change the Image from/to primary</summary>
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internal override bool PrimaryHDU
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{
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set
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myHeader.Xtension = "IMAGE";
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}
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}
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}
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}
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/// <summary>
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/// returns ImageTiler instance
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/// </summary>
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public virtual ImageTiler Tiler => ((ImageData)myData).Tiler;
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/// <summary>Build an image HDU using the supplied data.</summary>
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/// <param name="obj">the data used to build the image.</param>
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/// <exception cref="FitsException">If there was a problem with the data.</exception>
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/// <summary>The number of channels (planes) in the image.
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/// For 2D images this is 1. For 3D images this is the size of the first axis.</summary>
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public int ChannelCount => ((ImageData)myData).ChannelCount;
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/// <summary>Get a single channel (plane) of image data as a rectangular array.
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/// For 2D images, index must be 0 and returns the full image.
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/// For 3D images, returns the Nth channel as a rectangular 2D array (e.g. float[,]).
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/// </summary>
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/// <param name="index">The zero-based channel index.</param>
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public Array GetChannel(int index) => ((ImageData)myData).GetChannel(index);
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/// <summary>Build an image HDU using the supplied data.</summary>
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/// <param name="obj">the data used to build the image.</param>
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/// <exception cref="FitsException">If there was a problem with the data.</exception>
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public ImageHDU(Header h, Data d)
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{
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myData = d;
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myHeader = h;
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}
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/// <summary>Check that this HDU has a valid header for this type.</summary>
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/// <returns> <CODE>true</CODE> if this HDU has a valid header.</returns>
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/// <summary>Check that this HDU has a valid header for this type.</summary>
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/// <returns> <CODE>true</CODE> if this HDU has a valid header.</returns>
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public new static bool IsHeader(Header hdr)
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{
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bool found = false;
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return !hdr.GetBooleanValue("GROUPS");
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}
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/// <summary>Check if this object can be described as a FITS image.</summary>
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/// <param name="o">The Object being tested.</param>
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/// <summary>Check if this object can be described as a FITS image.</summary>
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/// <param name="o">The Object being tested.</param>
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public static bool IsData(Object o)
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{
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// Removed multidimension Array check logic: "(typeof(Array).Equals(o.GetType()) || o.GetType().FullName.IndexOf("[")!=-1)"
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// return (o != null) && o.GetType().IsArray && (!ArrayFuncs.GetBaseClass(o).Equals(typeof(bool)));
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return (o != null) && o.GetType().IsArray && (ArrayFuncs.GetBaseClass(o).IsPrimitive && !(ArrayFuncs.GetBaseClass(o).Equals(typeof(bool))));
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}
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/// <summary>Create a Data object to correspond to the header description.</summary>
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/// <returns> An unfilled Data object which can be used to read in the data for this HDU.</returns>
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/// <exception cref=""> FitsException if the image extension could not be created.</exception>
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return (o != null) && o.GetType().IsArray && (ArrayFuncs.GetBaseClass(o).IsPrimitive && !(ArrayFuncs.GetBaseClass(o).Equals(typeof(bool))));
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}
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/// <summary>Create a Data object to correspond to the header description.</summary>
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/// <returns> An unfilled Data object which can be used to read in the data for this HDU.</returns>
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/// <exception cref=""> FitsException if the image extension could not be created.</exception>
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internal override Data ManufactureData()
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{
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return ManufactureData(myHeader);
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return new ImageData(hdr);
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}
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/// <summary>Create a header that describes the given image data.</summary>
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/// <param name="o">The image to be described.</param>
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/// <exception cref=""> FitsException if the object does not contain valid image data.</exception>
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/// <summary>Create a header that describes the given image data.</summary>
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/// <param name="o">The image to be described.</param>
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/// <exception cref=""> FitsException if the object does not contain valid image data.</exception>
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public static Header ManufactureHeader(Data d)
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{
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if (d == null)
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return h;
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}
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/// <summary>Encapsulate an object as an ImageHDU.</summary>
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/// <summary>Encapsulate an object as an ImageHDU.</summary>
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public static Data Encapsulate(Object o)
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{
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return new ImageData(o);
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}
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/// <summary>Print out some information about this HDU.</summary>
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}
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/// <summary>Print out some information about this HDU.</summary>
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public override void Info()
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{
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if (IsHeader(myHeader))
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Console.Out.WriteLine(" Unable to get data");
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}
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}
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}
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}
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}
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}

‎IMPROVEMENTS.md‎

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Changes since forking from [rwg0/csharpfits](https://github.com/rwg0/csharpfits).
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## v4.2.0
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### Hybrid arrays for 3D+ images and channel access API
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For images with 3 or more dimensions (e.g. multi-channel), `DataArray` now returns a
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hybrid structure: a jagged outer `Array[]` of rectangular inner arrays. For example,
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a 3-channel 4176x6248 float image returns `Array[3]` of `float[4176, 6248]` instead of
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a single `float[3, 4176, 6248]`. This reduces the maximum single allocation from 299MB
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to ~100MB, which is much friendlier to the GC and Large Object Heap.
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1D and 2D images are unchanged (return `float[]` or `float[,]` respectively).
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New API for convenient channel access:
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```csharp
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ImageHDU hdu = ...;
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int n = hdu.ChannelCount; // 1 for 2D, N for 3D+
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float[,] red = (float[,])hdu.GetChannel(0); // first channel
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float[,] green = (float[,])hdu.GetChannel(1); // second channel
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```
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Also available on `ImageData` directly: `ChannelCount` and `GetChannel(int index)`.
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## v4.1.0
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### SIMD write path and buffered stream bypass

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