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how to get Mod 256 of image using opencv in java

asked 2018-06-24 07:33:54 -0500

vishalsira gravatar image

I am completely new user about opencv can anyone please suggest me how to take mod 256 of image using opencv in java

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what are you trying to achieve ? what do you need it for ?

berak gravatar imageberak ( 2018-06-24 08:32:47 -0500 )edit

i'm trying to encrypt image using some specific algorithm so i need to find out mod 256 of image

vishalsira gravatar imagevishalsira ( 2018-06-24 08:37:19 -0500 )edit

are you sure, that opencv is the right library for you ?

and it's still unclear, what exactly you're trying to do. do you have a formula, or similar ?

berak gravatar imageberak ( 2018-06-24 08:38:53 -0500 )edit

yes, i think opencv is more better for me

vishalsira gravatar imagevishalsira ( 2018-06-24 08:42:14 -0500 )edit

again, please try to explain what your assigment is about in more detail, else we cannot help you.

( mod 256 of image ) on it's own does not make any sense.

berak gravatar imageberak ( 2018-06-24 08:46:17 -0500 )edit

i want to generate shares of image using additive modulo

vishalsira gravatar imagevishalsira ( 2018-06-24 09:21:53 -0500 )edit

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answered 2018-06-24 09:25:28 -0500

berak gravatar image

there is no such builtin operation. (opencv will rather saturate pixels for builtin additions/subtractions and such.)

so (assuming a single channel uchar image) you'll have to:

// 1. get to the pixels:
byte bytes = new bytes[img.total()];
img.get(0,0,bytes); // copy.

// 2. java's byte type is *signed*, [-127,+127]
// so you have to cast every single one to an integer, before you can do maths on it
// ex.
int A = 0x7f + (int)bytes[i]; // to [0..255] range
int B = 200; // some number from your algorithm
int C = (A + B) % 256; // here's the modulo !
byte result = (byte)(C - 0x7f); // convert back
bytes[i] = result;

// 3. write back the pixels:
img.put(0,0,bytes);

as you can see, it's all very clumsy. neither opencv, nor java are a good choice for this.

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why you declare variable B ?

vishalsira gravatar imagevishalsira ( 2018-06-24 13:15:22 -0500 )edit

i'm just guessing that. again,you failed to tell us, where that would be coming from

berak gravatar imageberak ( 2018-06-24 13:17:51 -0500 )edit
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Asked: 2018-06-24 07:33:54 -0500

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Last updated: Jun 24 '18