Java buffered greyscale image byte and int -
please, please can explain below me. driving me nuts. playing creating 8-bit grayscale images arrays in java.
the code below should produce black > white horiz gradients. parts 1 , 2 produce desired image, in int[] passed getimagefromarray in 1 goes -128 127, , in 2 goes 0 255, yet produce same image. 3 produces (undesired) image expected 1 produce, going on max , min values alone.
why this? how can be?
import java.awt.image.bufferedimage; import java.awt.image.writableraster; import java.io.fileoutputstream; import java.io.ioexception; import javax.imageio.imageio; public class test { final static int width = 320; final static int height = 256; // black , white int final static int black = 0; final static int white = 255; //...same, not final static int black_wrong = 127; final static int white_wrong = -128; // black , white byte val final static byte black_byte = -0x80; //i.e -128 final static byte white_byte = 0x7f; // i.e. 127 public static void main(string[] args) throws ioexception { int[] pixels = new int[width*height]; int[] m; // generates gradient1.bmp // produces expected - black @ top, white @ bottom int numb=0,c=0; byte grey1 = black; while (numb<pixels.length){ // inc through greyscales down image if (c>width){ grey1++; c=0; } // cast byte int pixels[numb] = grey1; // inc column , count c++; numb++; } m = getmaxmin(pixels); // max 127 , min -128 system.out.printf("maxmin %s; %s;\n",m[0], m[1]); getimagefromarray("gradient1.bmp", pixels,width, height); //************************************************************************* // generates gradient3.bmp // produces expected - black @ top, white @ bottom numb=0; c=0; int grey2 = black; //i.e 0 while (numb<pixels.length){ // inc through greyscales down image if (c>width){ grey2++; c=0; } // no cast pixels[numb] = grey2; // inc column , count c++; numb++; } m = getmaxmin(pixels); // max 255, min 0 system.out.printf("maxmin %s; %s;\n",m[0], m[1]); getimagefromarray("gradient2.bmp", pixels,width, height); //************************************************************************* // generates gradient3.bmp // produces unexpected - midgrey > white. black > midgrey numb=0; c=0; byte grey3 = black_byte; //i.e 0 while (numb<pixels.length){ // inc through greyscales down image if (c>width){ grey3++; c=0; } // no cast pixels[numb] = grey3; // inc column , count c++; numb++; } m = getmaxmin(pixels); // max 127 , min -128 system.out.printf("maxmin %s; %s;\n",m[0], m[1]); getimagefromarray("gradient3.bmp", pixels,width, height); } //******************************************************************************* static int swidth,sheight = 0; static bufferedimage simage = null; static writableraster sraster=null; public static bufferedimage getimagefromarray(string filename, int pixels[], int width, int height) throws ioexception { if (simage == null){ simage = new bufferedimage(width, height, bufferedimage.type_byte_gray); sraster = simage.getraster(); } sraster.setpixels(0,0,width,height,pixels); try { imageio.write(simage, "bmp", new fileoutputstream(filename)); } catch (ioexception e) { e.printstacktrace(); } return simage; } static int[] getmaxmin(int[] v){ int max=0,min=0; (int i:v){ if (i>max) max = i; if (i<min) min = i; } int[] r = {max,min}; return r; } }
assuming bufferedimage takes rgba (or similarly) encoded colors input, needs construct ints respective rgba components.
to convert signed bytes r = 0, g = 0, b = 0, a = 127 gray, you'd have convert them unsigned ints , combine them 1 int, so:
int color = (((a & 0xff) << 24 | ((b & 0xff) << 16) | ((g << 8) | (r & 0xff)); this same assigning hex values of 7f 7f 7f ff. & 0xff masking necessary convert signed bytes (-128 127) unsigned int (0 255).
the << 'left shifts' bytes around inside int.
you may have change input order of rgba correct result.
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