Anthony Thyssen wrote:
Patrick Husson on wrote...
| Hi,
|
| I am writing a simple c++ program that hides data in a PNG image by
| replacing insignificant bits with bits from a message on a linux box
| using the most recent release of ImageMagick.
|
See IM examples, Stengo
http://imagemagick.org/Usage/transform/#stegano
| However, using the
| functions outlined in the Magick++ tutorial doesn't seem to modify the
| image.
|
| Let's say I want to hide the number of bits I am going d to use to hide
| data in the first red pixel byte in the image.
|
| Bits per byte used: 1
| Red1 = 0 //read from the image
| Red2 = 1 //modifed value that should replace the original red value
|
| To do this, I read the color of the first pixel and then get the red value
| //x=0,y=0
| Color firstPix = original.pixelColor(x,y); //original is the image
| unsigned char redVal = firstPix.redQuantum(); //MaxRGB = 255
|
| After doing operations, redVal becomes the value I want (1) and then it
| is written
| firstPix.redQuantum(modRedVal);
|
| Then the rest of the image is read row by row (y staying the same)
| x++;
|
| However, a program that reads the value from the modifed image shows
| that the
| values haven't changed:
|
| Color firstPix = image.pixelColor(x,y); //(0,0);
| unsigned char redVal = firstPix.redQuantum();
|
| output with cout << (int) redVal
| Red 1 = 0
|
| which gives the wrong number of bits to use:
| BitsUsed = 0
| .
At some point you should have a syncImage, to place the modified pixels
back into the image.
Best idea is to first look at the IM Web sites, Archeture page which has
the basic methods that IM uses.
http://imagemagick.org/script/architecture.php
All methods involve extracting pixels, modifying then placing the paixel
basic into the image structure.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
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Thanks for your help. I fixed the program last week and now it works
correctly.
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