Bitmap color change while compressing to png

Question

I\'m currently working on a steganogrpahy android app as a class project. I\'ve created an object that will encode an image with in another image and return an encoded bitma

Answer 1

For anyone who stumbles upon it, like me, wondering why bitnap colors change once you write it out in PNG. I have found out that using bitmap.setPreMultiplied(false) before calling bitmap.compress(PNG, 100, fileout) preserves the color of your image if it has alpha channel values. Setpremultiplied prevents the pixels written onto disk from being multiplied by alpha channel, thus generating different pixel color values.

Answer 2

Ok, after many long wasted hours worrying about the thread and the algorithm I was using to encode the the bitmap the problem was a little simpler. While decoding the image file that was to be encoded with a message I was using options.inPreferredConfig = Config.ARGB_8888; During debugging I was checking to make sure this didn't change to RGB_565. Although the bitmap object was loaded as ARBG_8888 the image file did not contain an alpha channel and thus even though the bitmap had a byte for the alpha level and would allow me to edit the alpha byte of a pixel through Bitmap.setPixel( x, y, color) the bitmap object never recognized that it had alpha values set. When compressing the bitmap compressed to RGB_565 since the object thought that there was no alpha channel. Somehow this problem was resolved by passing the bitmap to a sub activity and parsing it. I'm guessing when object was being recreated the alpha values I had set were recognized. To solve the problem with out passing the bitmap to a subactivity one must add an alpha channel after decoding a bitmap from a file. I found a function to do so here.

private Bitmap adjustOpacity( Bitmap bitmap )
{
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();
    Bitmap dest = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    int[] pixels = new int[width * height];
    bitmap.getPixels(pixels, 0, width, 0, 0, width, height);
    dest.setPixels(pixels, 0, width, 0, 0, width, height);
    return dest;
} 

I'm not sure if there is a more efficient method