Creating an image from an array of data is an easy task, but to create a byte-array of data from an image is a little more complicated. But it's required if you want to send a modified image to a server.

To create a byte-array of data from an image, we can use the getRGB(..) method in the image class in MIDP 2.0. From the getRGB method we get an int-array of data containing all the ARGB values of each pixel in the image. Integers in java are four bytes, so we need to split each int value into four byte values.

To mask out each of the bytes in the int we can use the 'AND &' operator and the 'shift-right >>' operator. Here's an example:

int ARGB = 0xFFFFFFFF;  // AARRGGBB 

int a = (ARGB & 0xFF000000); 

int r = (ARGB & 0x00FF0000); 

int g = (ARGB & 0x0000FF00); 

int b = (ARGB & 0x000000FF);

// Here we move each bit to the right.

a = (a >> 24); // a = 0x000000FF 

r = (r >> 16); // r = 0x000000FF 

g = (g >> 8); // g = 0x000000FF

b = b;        // b = 0x000000FF

When we convert the integer to a byte, there are some problems since there are only signed bytes in Java. A byte may contain values between –128 and 127 and from our integer we'll have a value between 0 and 255.

Here are some conversion examples:

Integer val 127 = byte val 127. 

Integer val 128 = byte val –128. 

Integer val 255 = byte val –1.

byte ba = (byte)(a);  // if a=0x000000FF (255), then ba = -1

byte br = (byte)(r); 

byte bg = (byte)(g); 

byte bb = (byte)(b);

We have to loop though each pixel in the image and get each pixel value to our byte-array. When that's done, we can send the image to a server where we can convert the byte-array back to a integer-array and then show our picture.

So, when we convert the byte back to an integer we have to check if the byte value is less than zero.

Int a, r, g, b;

If(ba<0)

     a = 256 – a;

Now our new integer value will be between 0 and 255 and we just have to use the 'shift-left <<' operator and add the values together to get our new int-array.

a = (a << 24);

r = (r << 16);

g = (g << 8);

b = (b);

  0xFF000000 (a)

+ 0x00FF0000 (r)

+ 0x0000FF00 (g)

+ 0x000000FF (b)

= 0xFFFFFFFF (argb)

int ARGB = a+r+g+b;

After the integer-array is recreated we can use the createRGBImage(..) method in the Image class to create our image.

Be aware that the byte-array is quite large as it contains all of the ARGB values for each pixel. If an image is 100*60 px, where each pixel is four bytes, the byte array will be 24kb.

ImageBytearryConvert.rar

在这里，当v添加第11个Integer的时候，v就会自动创建一个长度为20的数组（当前容量+增量），以后每次装满数组，都会重新按增量追加数组长度。
所以，设置一个合适的初始容量和增量，将会提高Vector的效率。千万别像我一样，把它当做链表。因为链表在增长空间时是不会影响到以前使用的空间和数据的。

我想指出一点，因为Vector中存储的，实际上都是Object变量，大家可以把它理解为指针。重新初始化Vector内置的数组并且拷贝，相当于对一个指针数组进行操作，并不等同于对输入类型的重新分配内存。
就是说Vector的重新分配，不论进行多少次都不涉及到Integer对象的创建，拷贝等工作。它只是重新创建并拷贝“指针”数组，也就是Object数组。
此外，java中有一个容易被忽视的基本概念。当某个对象再没有指向该对象的引用时，垃圾回收器才会自动将其自动释放。不小心使用，很容易给程序造成内存问题。
例如：

如下图 2 所示，您可以下拉所有功能组的许可设置，如“ Network Access ”就有 4 个选项可以修改： Ask first time 、 Ask every time 、 Always allowed 和 Not allowed ：

example code

• Use the getRGB(...) method in the image class to get all the ARGB values from the image to a int array.
• Use the blend function below to change the alpha value for each value in the array.
• Use the createRGBImage(...) method in the image class to create a new image from the edited int array.