Question

I’m trying to process some imagedata which comes directly from the device camera. In order to understand the CGImage structure, I’m using a buffer to create an image which doesn’t work right for me (I know that I shouldn’t use C code within Obj-C Code, it’s just for understanding). The code is as follows:

int *outBuf = malloc(sizeof(int) * width * height);
for (int i = 0; i < width * height;i ++)
{
     outBuf[i] = (((float)i) / ((float) width * height)) * 255.f;
}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

CGContextRef ctx = CGBitmapContextCreate(outBuf, width, height, 8, width * 4, colorSpace, kCGImageAlphaNone);

CGImageRef img = CGBitmapContextCreateImage(ctx);
CFRelease(ref);
CGContextRelease(ctx);
free(outBuf);

CGColorSpaceRelease(colorSpace);

[view.imgView setImage: [UIImage imageWithCGImage:img]];

CGImageRelease(img);

This should create a gradient from the very first to the very last pixel, but it results in a weird graphic:

Where do the horizontal spacings come from? (I want to solve this issue, I’m aware that there are other possibilities to draw the gradient) Thanks in advance.

Answer 1

I’ve found the solution:

I was initialising the buffer with int*. Every int is 4 bytes long, but a grayscale picture just needs 1 byte per pixel. Changing the buffer to char* and modifying the CGBitmapContextCreate parameters fixed the issue:

CGBitmapContextCreate(outBuf, width, height, 8, width, colorSpace, kCGImageAlphaNone);