bitmappixels

To perform any image processing operations on an image, we must have an image object in native part like we have a Bitmap object in Java. We cannot just pass the image bitmap object directly as an argument to native function because ‘Bitmap’ is a java object and C/C++ cannot interpret it directly as an image. So, here I’ll discuss a method to send java Bitmap object to Native part for performing image processing operations on it, which we implemented in the image editor of Phimpme Android Image Application. C/C++ cannot interpret java bitmap object. So, we have to find the pixels of the java bitmap object and send them to native part to create a native bitmap over there. In Phimpme, we used a “struct” data structure in C to represent native bitmap. An image has three color channels red, green, blue. We consider alpha channel(transparency) for an argb8888 type image. But in Phimpme, we considered only three channels as it is enough to manipulate these channels to implement the edit functions, which we used in the Editor of Phimpme. We defined a struct, type-defined as NativeBitmap with attributes corresponding to all the three channels. We defined this in the nativebitmap.h header file in the jni/ folder of Phimpme so that we can include this header file in c files in which we needed to use a NativeBitmap struct. #ifndef NATIVEBITMAP #define NATIVEBITMAP #endif typedef struct { unsigned int width; unsigned int height; unsigned int redWidth; unsigned int redHeight; unsigned int greenWidth; unsigned int greenHeight; unsigned int blueWidth; unsigned int blueHeight; unsigned char* red; unsigned char* green; unsigned char* blue; } NativeBitmap; void deleteBitmap(NativeBitmap* bitmap); int initBitmapMemory(NativeBitmap* bitmap, int width, int height); As I explained in my previous post here on introduction to flow of native functions in Phimpme-Android, we defined the native functions with necessary arguments in Java part of Phimpme. We needed the image bitmap to be sent to the native part of the Phimpme application. So the argument in the function should have been java Bitmap object. But as mentioned earlier, the C code cannot interpret this java bitmap object directly as an image. So we created a function for getting pixels from a bitmap object in the Java class of Phimpme application. This function returns an array of unsigned integers which correspond to the pixels of a particular row of the image bitmap. The array of integers can be interpreted by C, so we can send this array of integers to native part and create a receiving native function to create NativeBitmap. We performed image processing operations like enhancing and applying filters on this NativeBitmap and after the processing is done, we sent the array of integers corresponding to a row of the image bitmap and constructed the Java Bitmap Object using those received arrays in java. The integers present in the array correspond to the color value of a particular pixel of the image bitmap. We used this color value to get red, green…