How can i save an image and read it again without change its value ?

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budi agung 2017-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/333229-how-can-i-save-an-image-and-read-it-again-without-change-its-value

评论： Walter Roberson 2019-1-21

im doing watermarking image using DWT and got problem about the value change when i try to read the watermarked image

imwrite(Watermarkedimage_final ,'iwater.bmp');
   x=imread('iwater.bmp');
x=im2double(x);
[F11,F22]= wfilters('haar', 'd');
[a b c d]=dwt2(x,'haar','d');
[aa bb cc dd]=dwt2(a,'haar','d');
[aaa bbb ccc ddd]=dwt2(aa,'haar','d');
recovered_image=imadjust(recovered_image);
imshow(uint8(recovered_image),[]);
imwrite(recovered_image ,'bmp.bmp');

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回答（3 个）

Image Analyst 2017-4-2

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Watermarkedimage_final and the badly-named "x" will have the same values because BMP is a lossless format.

Likewise, if you use imread to read in the badly-named 'bmp.bmp' then the recalled image will have the same values as uint8(recovered_image).

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budi agung 2017-4-2

ok thanks.

can i imwrite image in double data type ?

Image Analyst 2017-4-2

Use save() to save it to a .mat file.

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Walter Roberson 2017-4-2

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Sorry, No, MATLAB does not support any double precision floating point image formats. It supports single precision TIFF; see https://www.mathworks.com/matlabcentral/answers/7184-how-can-i-write-32-bit-floating-point-tifs-with-nans#comment_15023 .

TIFF 6.0 added support for IEEE double precision but MATLAB is not able to write those out.

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Walter Roberson 2017-4-5

The TIFF class can only handle single precision. The TIFF file format revision 6 and later can handle double precision, but imwrite() and the TIFF class cannot write version 6 TIFF files.

In other words, if you need to be able to write the watermarked data as an image file, you have three choices:

find a way to write TIFF 6 double precision files -- which your display program probably would not be able to display anyhow; or
use an integer-to-integer DWT instead of a double precision DWT; or
modify the values in such as way that after writing to file and reading back in the changed data is reliably distinguishable from the original values and can be processed to extract the watermark.

LSB (Least Significant Bit) modifications of the double precision wavelet transform are not enough to be able make recoverable changes.

I suggest you look at https://www.mathworks.com/matlabcentral/answers/?term=tag%3A%22iwt%22

Walter Roberson 2019-1-21

There is a File Exchange contribution that claims to be able to write double precision TIFF.

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budi agung 2017-4-5

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在 MATLAB Online 中打开

this is my code

 clc
close all
%host
cover=imresize(imread('host.jpg'),[256 256]);
%rgbimage=rgb2gray(rgbimage);
cover=im2double(cover);
[F1,F2]= wfilters('haar', 'd');
figure;imshow(cover);title('original color image');
[h_LL,h_LH,h_HL,h_HH]=dwt2(cover,'haar', 'd');
[h_LL2,h_LH2,h_HL2,h_HH2]=dwt2(h_LL,'haar', 'd');
 [nRow nCol noDim] = size(h_LL2);
water=imresize(imread('watermark.jpg'),[nRow nCol]);
%water=rgb2gray(water);
water=im2double(water);
%watermarking
 newhost_LL = h_LL2 +0.1*water;
 %output
 hasil1=idwt2(newhost_LL,h_LH2,h_HL2,h_HH2,'haar', 'd');
hasil1=idwt2(hasil1,h_LH,h_HL,h_HH,'haar', 'd');
 figure;imshow(hasil1);title('Watermarked image');
imwrite(hasil1,'Watermarked.bmp','bmp');
 %extracted
watermarked=imread('watermarked.bmp');
watermarked=im2double(watermarked);
[wm_LL,wm_LH,wm_HL,wm_HH]=dwt2(watermarked,'haar', 'd');
[wm_LL2,wm_LH2,wm_HL2,wm_HH2]=dwt2(wm_LL,'haar', 'd');
 newwatermark_LL= (wm_LL2-h_LL2)/0.1;
 figure;imshow(newwatermark_LL);title('Extracted watermark');
 %imwrite(newwatermark_LL,'EeweWatermark.bmp');