What is the use of "maxidx = max(A(:))+1" in the below code ? How does it work? Any alternate syntax for the below function?

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Samson David Puthenpeedika
评论： Samson David Puthenpeedika 2021-11-9
Ran in:
The question and code is given below :-
input: spine.tif from MATLAB
Read the indexed image with the associated colormap, show the colormap functions of all color channels with the corresponding color;
[A,map]=imread("spine.tif");
maxidx = max(A(:))+1;
figure()
hold on;
plot(map(1:maxidx,1),'r')
plot(map(1:maxidx,2),'g')
plot(map(1:maxidx,3),'b')
hold off
Can someone explain the use of "maxidx = max(A(:))+1;" in this code .
Like what did the above code do?
Is there any syntax to do the above function?

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Stephen23
Stephen23 2021-11-8
编辑：Stephen23 2021-11-8
Ran in:
"Can someone explain the use of "maxidx = max(A(:))+1;" in this code"
The answer can be derived from https://www.mathworks.com/help/matlab/creating_plots/image-types.html
The image file contains an indexed image, stored using integer indices:
class(imread("spine.tif"))
ans = 'uint8'
imfinfo("spine.tif")
ans = struct with fields:
Filename: '/MATLAB/toolbox/images/imdata/spine.tif' FileModDate: '14-Apr-2015 15:06:00' FileSize: 73166 Format: 'tif' FormatVersion: [] Width: 490 Height: 367 BitDepth: 8 ColorType: 'indexed' FormatSignature: [73 73 42 0] ByteOrder: 'little-endian' NewSubFileType: 0 BitsPerSample: 8 Compression: 'PackBits' PhotometricInterpretation: 'RGB Palette' StripOffsets: [8 289 4019 8116 12408 16005 19646 23350 26632 29577 31936 34376 36508 38024 39717 41397 43125 46361 50216 54920 60170 65751 67261] SamplesPerPixel: 1 RowsPerStrip: 16 StripByteCounts: [281 3730 4097 4292 3597 3641 3704 3282 2945 2359 2440 2132 1516 1693 1680 1728 3236 3855 4704 5250 5581 1510 120] XResolution: 72 YResolution: 72 ResolutionUnit: 'Inch' Colormap: [256×3 double] PlanarConfiguration: 'Chunky' TileWidth: [] TileLength: [] TileOffsets: [] TileByteCounts: [] Orientation: 1 FillOrder: 1 GrayResponseUnit: 0.0100 MaxSampleValue: 255 MinSampleValue: 0 Thresholding: 1 Offset: 71244 ImageDescription: ''
"Like what did the above code do?"
Converts the maximum index of a integer indexed image (i.e. zero-based) into a MATLAB index (i.e. one-based).
"Is there any syntax to do the above function?"
What function?
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Stephen23
Stephen23 2021-11-9
Ran in:
" Is there any other way or alternate solution to show the colormap functions of all color channels with the corresponding color"
[A,map] = imread("spine.tif");
mx = 1+max(A(:));
rgbplot(map(1:mx,:))
Compared against the original approach:
figure()
hold on;
plot(map(1:mx,1),'r')
plot(map(1:mx,2),'g')
plot(map(1:mx,3),'b')

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