MATLAB: How to write a TIFF image into a 16 bit signed integer file using IMWRITE in MATLAB 7.11 (R2010b)

MATLAB

I am trying to save a TIFF file of a digital elevation model (DEM) with absolute heights in meters above or below sea level. To do this correctly, IMWRITE must write a 16-bit signed integer file (to handle negative integers). But, IMWRITE supports only unsigned integers.

Best Answer

The ability to write a TIFF image into a 16 bit signed integer file using IMWRITE is not available in MATLAB 7.11 (R2010b).

To work around this issue, use TIFF class. For more information on writing TIFF objects, visit:

 <http://www.mathworks.com/access/helpdesk/help/techdoc/ref/tiff.write.html>

Related Solutions

MATLAB: How to convert a 24 bit depth image file to an 8 bit depth image file

To achieve the bit depth conversion, use the RGB2IND function. The following code sample illustrates this:

RGB = imread('myimage.tif')
[X,map] = rgb2ind(RGB, 256);
imwrite(X,map,'myindexedimage.tif');

Now myindexedimage.tif has a bit depth of 8.

Note IM2UINT8 and the IM2UINT16 functions, are also useful when attempting to convert between different bit depths. The following code sample illustrates the conversion from a 8 bit depth image to a 24 bit depth image. 'trees.tif' is an image shipped with the Image processing toolbox that has a bit depth of 8.

[Xtrees,maptrees] = imread('trees.tif');
XtreesRGB = ind2rgb(Xtrees,maptrees);
XtreesRGB = im2uint8(XtreesRGB);
imwrite(Xtreesind,'myindexedtrees.tiff')
imfinfo('myindexedtrees.tiff')
 ans = 
                      Filename: 'myindexedtrees.tiff'
                   FileModDate: '08-May-2008 09:48:27'
                      FileSize: 259354
                        Format: 'tif'
                 FormatVersion: []
                         Width: 350
                        Height: 258
                      BitDepth: 24
                     ColorType: 'truecolor'
               FormatSignature: [73 73 42 0]
                     ByteOrder: 'little-endian'
                NewSubFileType: 0
                 BitsPerSample: [8 8 8]
                   Compression: 'PackBits'
     PhotometricInterpretation: 'RGB'
                  StripOffsets: [37x1 double]
               SamplesPerPixel: 3
                  RowsPerStrip: 7
               StripByteCounts: [37x1 double]
                   XResolution: 72
                   YResolution: 72
                ResolutionUnit: 'Inch'
                      Colormap: []
           PlanarConfiguration: 'Chunky'
                     TileWidth: []
                    TileLength: []
                   TileOffsets: []
                TileByteCounts: []
                   Orientation: 1
                     FillOrder: 1
              GrayResponseUnit: 0.0100
                MaxSampleValue: [255 255 255]
                MinSampleValue: 0
                  Thresholding: 1

MATLAB: How to save a Tiff using signed values with LibTiff library.

You need one extra tag:

intFinalImage = int16(magic(10));
tiffFile = 't.tif';
t = Tiff(tiffFile,'w');
%-----------------------------------------------

tagstruct.SampleFormat = Tiff.SampleFormat.Int;
%-----------------------------------------------
tagstruct.ImageLength = size(intFinalImage,1);
tagstruct.ImageWidth = size(intFinalImage,2);
tagstruct.Photometric = Tiff.Photometric.MinIsBlack;
tagstruct.BitsPerSample = 16;
tagstruct.SamplesPerPixel = 1;
tagstruct.RowsPerStrip = 16;
tagstruct.PlanarConfiguration = Tiff.PlanarConfiguration.Chunky;
tagstruct.Software = 'MATLAB';
t.setTag(tagstruct)
t.write(intFinalImage(:,:,1));
t.close();
d = imread(tiffFile);
class(d)
ans =
int16

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Related Solutions

MATLAB: How to convert a 24 bit depth image file to an 8 bit depth image file

MATLAB: How to save a Tiff using signed values with LibTiff library.

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