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POInvert pixels - zxing
 

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    <p>I'm using a zxing library in my iOS project. It's a library for reading and creating QR Codes.</p> <p>From my researching and browsing around the web the process of decoding the image is made of this steps:</p> <ul> <li>takes an image from source, </li> <li>converts all the pixels to 255 grayscale</li> <li>decodes the data</li> </ul> <p>One thing which is not supported by this specific library is reading/decoding (and I'm pretty sure that this is missing in creating also) of inverted QRCodes. </p> <p>Inverted QR Codes are basicly the same as normal codes -> but with inverted colors (white is black and black is white). But because the QRCodes standard doesn't describe the inverted QRCodes implementation and on zxing project website there is a few requests and issues, I must implement this by myself.</p> <p>The method below is a good place to insert some logic to invert the pixels (<code>unsigned char*</code>), but because of my non-experience with C++ the result is this writing.</p> <p>The <code>grayData_</code> is a <code>unsigned char*</code> data type. And inside this variable there are grayScaled pixels from source. </p> <p>What I want to do is invert these pixels.</p> <p>If I'm correct this is done by <code>unsigned char cz = (255 - val);</code>?</p> <pre><code>unsigned char* GreyscaleLuminanceSource::getMatrix() { int size = width_ * height_; unsigned char* result = new unsigned char[size]; if (left_ == 0 &amp;&amp; top_ == 0 &amp;&amp; dataWidth_ == width_ &amp;&amp; dataHeight_ == height_) { memcpy(result, greyData_, size); } else { for (int row = 0; row &lt; height_; row++) { memcpy(result + row * width_, greyData_ + (top_ + row) * dataWidth_ + left_, width_); } } //return result; //from this point down is my implementation printf(" %c", result[200]); printf(" %c", result[600]); printf(" %c", result[6000]); printf(" %c", result[7000]); for (int i = 0; i &lt; size; i++) { int val = static_cast&lt;int&gt;(result[i]); unsigned char cz = (255 - val); result[i] = cz; } printf("******\n"); printf(" %c", result[200]); //prints a " " char to console/terminal printf(" %c", result[600]); //prints a " " char to console/terminal printf(" %c", result[6000]); //prints a " " char to console/terminal printf(" %c", result[7000]); //prints a " " char to console/terminal return result; } </code></pre> <p>Is this the right way to invert the pixels? And I'm not so happy with changing the data in the <code>result</code> variable.</p>
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