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POAndroid: Converting a Bitmap to a Monochrome Bitmap (1 Bit per Pixel)
 

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  1. POAndroid: Converting a Bitmap to a Monochrome Bitmap (1 Bit per Pixel)
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    <p>I want to print a Bitmap to a mobile Bluetooth Printer (Bixolon SPP-R200) - the SDK doesn't offer direkt methods to print an in-memory image. So I thought about converting a Bitmap like this:</p> <pre><code>Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); </code></pre> <p>To a Monochrome Bitmap. I am drawing black text on above given Bitmap using a Canvas, which works well. However, when I convert the above Bitmap to a ByteArray, the printer seems to be unable to handle those bytes. I suspect I need an Array with one Bit per Pixel (a Pixel would be either white = 1 or black = 0).</p> <p>As there seems to be no convenient, out of the box way to do that, one idea I had was to use: </p> <pre><code>bitmap.getPixels(pixels, offset, stride, x, y, width, height) </code></pre> <p>to Obtain the pixels. I assume, I'd have to use it as follows:</p> <pre><code>int width = bitmap.getWidth(); int height = bitmap.getHeight(); int [] pixels = new int [width * height]; bitmap.getPixels(pixels, 0, width, 0, 0, width, height); </code></pre> <p>However - I am not sure about a few things:</p> <ul> <li>In getPixels - does it make sense to simply pass the width as the "Stride" argument?</li> <li>I guess I'd have to evaluate the color information of each pixel and either switch it to black or white (And I'd write this value in a new target byte array which I would ultimately pass to the printer)?</li> <li>How to best evaluate each pixel color information in order to decide that it should be black or white? (The rendered Bitmap is black pain on a white background)</li> </ul> <p>Does this approach make sense at all? Is there an easier way? It's not enough to just make the bitmap black &amp; white, the main issue is to reduce the color information for each pixel into one bit.</p> <p><strong>UPDATE</strong></p> <p>As suggested by Reuben I'll first convert the Bitmap to a monochrome Bitmap. and then I'll iterate over each pixel:</p> <pre><code> int width = bitmap.getWidth(); int height = bitmap.getHeight(); int[] pixels = new int[width * height]; bitmap.getPixels(pixels, 0, width, 0, 0, width, height); // Iterate over height for (int y = 0; y &lt; height; y++) { int offset = y * height; // Iterate over width for (int x = 0; x &lt; width; x++) { int pixel = bitmap.getPixel(x, y); } } </code></pre> <p>Now Reuben suggested to "read the lowest byte of each 32-bit pixel" - that would relate to my question about how to evaluate the pixel color. My last question in this regard: Do I get the lowest byte by simply doing this:</p> <pre><code>// Using the pixel from bitmap.getPixel(x,y) int lowestByte = pixel &amp; 0xff; </code></pre>
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    1. COI have this QA starred because I was working on a similar concept with regards to programmatically manipulating arrays to become monochrome bitmaps. I have a question & its eventual answer here: http://stackoverflow.com/questions/17918978/plot-an-array-into-bitmap-in-c-c-for-thermal-printer If this helps people, please email me and I'll come up with a suitable answer to this question.
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