Why do Image Size Dimensions Change
in [Matlab]
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From: Rise on 8 Jul 2010 11:42 Hi, all, Am a newbie to Matlab and image processing. Have been reading the book, Digital Image Processing by Gonzales et al. But I have a question....if someone could explain in more detail to me... Why do the dimensions of the image change? Is it due to the conversion? e.g., I = imread('new-001.tif'); % dimensions for I: width: 1246, height: 912, uint8 I = im2double(rgb2gray(I)); % Now width = 1249, height = 914, double I am inquiring, because I would like to map the grayscale image, I, to another color image, J, of the same dimensions of I -- when 'I' was originally read in. But I would like to know why the dimensions of I changed in the first place. I am assuming it has something to do with the conversion. If you know of a link that I could read, please let me know. Thanks in advance. Sincerely, Rise
From: Steve Eddins on 8 Jul 2010 13:50 On 7/8/2010 11:42 AM, Rise wrote: > Hi, all, > Am a newbie to Matlab and image processing. Have been reading the book, > Digital Image Processing by Gonzales et al. But I have a question....if > someone could explain in more detail to me... > > Why do the dimensions of the image change? Is it due to the conversion? > e.g., > I = imread('new-001.tif'); % dimensions for I: width: 1246, height: 912, > uint8 > I = im2double(rgb2gray(I)); % Now width = 1249, height = 914, double > > I am inquiring, because I would like to map the grayscale image, I, to > another color image, J, of the same dimensions of I -- when 'I' was > originally read in. But I would like to know why the dimensions of I > changed in the first place. I am assuming it has something to do with > the conversion. > > If you know of a link that I could read, please let me know. > Thanks in advance. Sincerely, Rise Neither rgb2gray nor im2double should change the image size in this way. Possible explanations: * The image in the TIFF file is really 1249x914 instead of 1246x912. What is the output for: imfinfo('new-001.tif') size(imread('new-001.tif')) * You have modified versions of the functions im2double or rgb2gray on your path. What is the output for: which -all im2double which -all rgb2gray --- Steve Eddins http://blogs.mathworks.com/steve/
From: Rise on 8 Jul 2010 15:29 Hi, Steve, Here is the information that I get. Thnx for your assistance. - Rise >> imfinfo('new-002.tif') ans = Filename: 'new-002.tif' FileModDate: '03-May-2010 14:05:46' FileSize: 2898754 Format: 'tif' FormatVersion: [] Width: 1247 Height: 912 BitDepth: 24 ColorType: 'truecolor' FormatSignature: [73 73 42 0] ByteOrder: 'little-endian' NewSubFileType: 0 BitsPerSample: [8 8 8] Compression: 'PackBits' PhotometricInterpretation: 'RGB' StripOffsets: [456x1 double] SamplesPerPixel: 3 RowsPerStrip: 2 StripByteCounts: [456x1 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 Offset: 2894910 >> size(imread('new-002.tif')) ans = 912 1247 3 >> which -all im2double C:\Program Files\MATLAB\R2010a\toolbox\images\images\im2double.m >> which -all rgb2gray C:\Program Files\MATLAB\R2010a\toolbox\images\images\rgb2gray.m >>
From: Rise on 8 Jul 2010 15:44 Hi, Steve, I am looking at my code, and see where the dimensions are changing. I have the following: [I, map] = imread('new-002.tif'); I = im2double(rgb2gray(I)); gx = conv2(I,h); % extract horizontal edges of I gy = conv2(I,v); % extract vertical edges of I gm = sqrt(gx.*gx + gy.*gy); % magnitude It is here that my image apparently changes from >> size(imread('new-002.tif')) ans = 912 1247 3 to this: >> size(gm) ans = 914 1249 >> Hm. But I still don't understand why the dimensions are changing if I am using the gradient. Thnx in advance for your explanation. Sincerely, Rise
From: Rise on 8 Jul 2010 15:56
Hi, Steve, Here is more information re. conv2 and sqrt: >> which -all sqrt built-in (C:\Program Files\MATLAB\R2010a\toolbox\matlab\elfun\@double\sqrt) % double method built-in (C:\Program Files\MATLAB\R2010a\toolbox\matlab\elfun\@single\sqrt) % single method C:\Program Files\MATLAB\R2010a\toolbox\distcomp\parallel\@codistributed\sqrt.m % codistributed method >> which -all conv2 built-in (C:\Program Files\MATLAB\R2010a\toolbox\matlab\datafun\@single\conv2) % single method built-in (C:\Program Files\MATLAB\R2010a\toolbox\matlab\datafun\@double\conv2) % double method C:\Program Files\MATLAB\R2010a\toolbox\matlab\datafun\@uint8\conv2.m % uint8 method C:\Program Files\MATLAB\R2010a\toolbox\matlab\datafun\@uint16\conv2.m % uint16 method >> |