Compress image with PCM encoder

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Marian-Catalin Pirvulescu 2020-2-24

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https://ww2.mathworks.cn/matlabcentral/answers/507156-compress-image-with-pcm-encoder

回答： Pujitha Narra 2020-2-26

For an equation like x(t) = A*sin(2*pi*f*t) the result is code like this:

% Analog signal
f=2;    % Maximum freq of the input signal
fs=5*f;
t=0:1/fs:1;
a=2;
x=a*sin(2*pi*f*t);
% Amplitude shifting
x_pos=x+a;
% Quantization
quant=round(x_pos);
% Decimal to binary
encoder=de2bi(quant, 'left-msb');
% Receiver
decoder=bi2de(encoder,'left-msb');
% Shifting the amplitude back
x_out=decoder-a;

My question is, for a given .PGM image, how can I compress it with a PCM encoder following these steps (analog signal- sampler-quantizer-encoder-decoder) and change its bits per pixel?

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Walter Roberson 2020-2-24

The numeric values read in by imread() can already be considered to be quantized. However if you wanted, you could quantize further. For example, you might do

quant = round(TheImage, -1);

which would round uint8 or uint16 values to the nearest 10.

encoder=de2bi(quant, 'left-msb');

For consistency you should be passing in N, the minimum number of digits to use.

Marian-Catalin Pirvulescu 2020-2-24

Thank you, Walter!

For exemple, if my image is 8 bits per pixel and I want to change it to 5 bits per pixel and keep the .PGM format, how should I write the code?

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Answer 1

Pujitha Narra 2020-2-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/507156-compress-image-with-pcm-encoder#answer_417423

Hi,

This is one of the several submissions in MATLAB File Exchange. Feel free to contact the author of this submission directly for specific questions about the implementation.

https://www.mathworks.com/matlabcentral/fileexchange/34610-pcm-matlab-code?s_tid=answers_rc2-2_p5_MLT