I'm trying to create an UIImage test pattern for an iOS 5.1 device. The target UIImageView is 320x240 in size, but I was trying to create a 160x120 UIImage test pattern (future, non-test pattern images will be this size). I wanted the top half of the box to be blue and the bottom half to be red, but I get what looks like uninitialized memory corrupting the bottom of the image. The code is as follows:
int width = 160;
int height = 120;
unsigned int testData[width * height];
for(int k = 0; k < (width * height) / 2; k++)
testData[k] = 0xFF0000FF; // BGRA (Blue)
for(int k = (width * height) / 2; k < width * height; k++)
testData[k] = 0x0000FFFF; // BGRA (Red)
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, &testData, (width * height * 4), NULL);
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGImageAlphaNoneSkipFirst;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow,
colorSpaceRef, bitmapInfo, provider, NULL, NO,renderingIntent);
UIImage *myTestImage = [UIImage imageWithCGImage:imageRef];
This should look like another example on Stack Overflow. Anyway, I found that as I decrease the size of the test pattern the "corrupt" portion of the image increases. What is also strange is that I see lines of red in the "corrupt" portion, so it doesn't appear that I'm just messing up the sizes of components. What am I missing? It feels like something in the provider, but I don't see it.
Thanks!
Added screenshots. Here is what it looks like with kCGImageAlphaNoneSkipFirst set:
And here is what it looks like with kCGImageAlphaFirst:
Your pixel data is in an automatic variable, so it's stored on the stack:
unsigned int testData[width * height];
You must be returning from the function where this data is declared. That makes the function's stack frame get popped and reused by other functions, which overwrites the data.
Your image, however, still refers to that pixel data at the same address on the stack. (CGDataProviderCreateWithData doesn't copy the data, it just refers to it.)
To fix: use malloc or CFMutableData or NSMutableData to allocate space for your pixel data on the heap.
Your image includes alpha which you then tell the system to ignore by skipping the most significant bits (i.e. the "B" portion of your image). Try setting it to kCGImageAlphaPremultipliedLast instead.
EDIT:
Now that I remember endianness, I realize that the program is probably reading your values in backwards, so what you might actually want is kCGImageAlphaPremultipliedFirst
Related
I'm trying to generate a pixel buffer using a bitmap context on iOS (in ObjC). The abridged code (to remove null checks etc) is below.
CGFloat width = 1;
CGFloat height = 1;
CVPixelBufferRef buffer;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
width,
height,
kCVPixelFormatType_OneComponent8,
nil,
&buffer);
CVPixelBufferLockBaseAddress(buffer, 0);
void *data = CVPixelBufferGetBaseAddress(buffer);
CGColorSpaceRef space = CGColorSpaceCreateDeviceGray();
CGContextRef ctx = CGBitmapContextCreate(data,
width,
height,
8,
0,
space,
(CGBitmapInfo) kCGImageAlphaNoneSkipLast);
// ... draw into context
CVPixelBufferUnlockBaseAddress(buffer, 0);
This is trying to create a bitmap context for a single pixel, where both the input and the output pixels are 8-bit grayscale.
I get the following output (I added the bold):
CGBitmapContextCreate: invalid data bytes/row: should be at least 2 for 8 integer bits/component, 1 components, kCGImageAlphaNoneSkipLast.
Why does it double the expected bytes per row? This is consistent for the width / height combinations I've tried, and 'works' if I halve the width parameter in CGBitmapContextCreate. Note also that if I pass in a value for bytesPerRow then it still fails this check and gives the same output.
Am I missing something obvious?
Edit: formatting.
kCGImageAlphaNoneSkipLast was wrong. I needed to use kCGImageAlphaNone.
The bitmap create call now looks like:
CGContextRef ctx = CGBitmapContextCreate(data,
width,
height,
8,
CVPixelBufferGetBytesPerRow(buffer),
space,
kCGImageAlphaNone);
Android:
import android.graphics.Bitmap;
public void getPixels (int[] pixels, int offset, int stride, int x, int y, int width, int height);
Bitmap bmap = source.renderCroppedGreyscaleBitmap();
int w=bmap.getWidth(),h=bmap.getHeight();
int[] pix = new int[w * h];
bmap.getPixels(pix, 0, w, 0, 0, w, h);
Returns in pixels[] a copy of the data in the bitmap.
Each value is a packed int representing a Color.
The stride parameter allows the caller to allow for gaps in the returned pixels array between rows.
For normal packed results, just pass width for the stride value.
The returned colors are non-premultiplied ARGB values.
iOS:
#implementation UIImage (Pixels)
-(unsigned char*) rgbaPixels
{
// The amount of bits per pixel, in this case we are doing RGBA so 4 byte = 32 bits
#define BITS_PER_PIXEL 32
// The amount of bits per component, in this it is the same as the bitsPerPixel divided by 4 because each component (such as Red) is only 8 bits
#define BITS_PER_COMPONENT (BITS_PER_PIXEL/4)
// The amount of bytes per pixel, in this case a pixel is made up of Red, Green, Blue and Alpha so it will be 4
#define BYTES_PER_PIXEL (BITS_PER_PIXEL/BITS_PER_COMPONENT)
// Define the colour space (in this case it's gray)
CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
// Find out the number of bytes per row (it's just the width times the number of bytes per pixel)
size_t bytesPerRow = self.size.width * BYTES_PER_PIXEL;
// Allocate the appropriate amount of memory to hold the bitmap context
unsigned char* bitmapData = (unsigned char*) malloc(bytesPerRow*self.size.height);
// Create the bitmap context, we set the alpha to none here to tell the bitmap we don't care about alpha values
CGContextRef context = CGBitmapContextCreate(bitmapData,self.size.width,self.size.height,BITS_PER_COMPONENT,bytesPerRow,colourSpace,kCGImageAlphaFirst);//It returns null
/* We are done with the colour space now so no point in keeping it around*/
CGColorSpaceRelease(colourSpace);
// Create a CGRect to define the amount of pixels we want
CGRect rect = CGRectMake(0.0,0.0,self.size.width,self.size.height);
// Draw the bitmap context using the rectangle we just created as a bounds and the Core Graphics Image as the image source
CGContextDrawImage(context,rect,self.CGImage);
// Obtain the pixel data from the bitmap context
unsigned char* pixelData = (unsigned char*)CGBitmapContextGetData(context);
// Release the bitmap context because we are done using it
CGContextRelease(context);
//CGColorSpaceRelease(colourSpace);
return pixelData;
#undef BITS_PER_PIXEL
#undef BITS_PER_COMPONENT
}
But it can't work.
CGBitmapContextCreate(bitmapData,self.size.width,self.size.height,BITS_PER_COMPONENT,bytesPerRow,colourSpace,kCGImageAlphaFirst);
It returns NULL.
I need the same array as pix[ ] above,how can I make it?
I have some
CGImageRef cgImage = "something"
Is there a way to manipulate the pixel values of this cgImage? For example if this image contains values between 0.0001 and 3000 thus when I try to view or release the image this way in an NSImageView (How can I show an image in a NSView using an CGImageRef image)
I get a black image, all pixels are black, I think it has to do with setting the pixel range values in a different color map (I don't know).
I want to be able to manipulate or change the pixel values or just be able to see the image by manipulating the color map range.
I have tried this but obviously it doesn't work:
CGContextDrawImage(ctx, CGRectMake(0,0, CGBitmapContextGetWidth(ctx),CGBitmapContextGetHeight(ctx)),cgImage);
UInt8 *data = CGBitmapContextGetData(ctx);
for (**all pixel values and i++ **) {
data[i] = **change to another value I want depending on the value in data[i]**;
}
Thank you,
In order to manipulate individual pixels in an image
allocate a buffer to hold the pixels
create a memory bitmap context using that buffer
draw the image into the context, which puts the pixels into the
buffer
change the pixels as desired
create a new image from the context
free up resources (note be sure to check for leaks using instruments)
Here's some sample code to get you started. This code will swap the blue and red components of each pixel.
- (CGImageRef)swapBlueAndRedInImage:(CGImageRef)image
{
int x, y;
uint8_t red, green, blue, alpha;
uint8_t *bufptr;
int width = CGImageGetWidth( image );
int height = CGImageGetHeight( image );
// allocate memory for pixels
uint32_t *pixels = calloc( width * height, sizeof(uint32_t) );
// create a context with RGBA pixels
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate( pixels, width, height, 8, width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast );
// draw the image into the context
CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image );
// manipulate the pixels
bufptr = (uint8_t *)pixels;
for ( y = 0; y < height; y++)
for ( x = 0; x < width; x++ )
{
red = bufptr[3];
green = bufptr[2];
blue = bufptr[1];
alpha = bufptr[0];
bufptr[1] = red; // swaps the red and blue
bufptr[3] = blue; // components of each pixel
bufptr += 4;
}
// create a new CGImage from the context with modified pixels
CGImageRef resultImage = CGBitmapContextCreateImage( context );
// release resources to free up memory
CGContextRelease( context );
CGColorSpaceRelease( colorSpace );
free( pixels );
return( resultImage );
}
I just started to get my hands dirty with the Tesseract library, but the results are really really bad.
I followed the instructions in the Git repository ( https://github.com/gali8/Tesseract-OCR-iOS ). My ViewController uses the following method to start recognizing:
Tesseract *t = [[Tesseract alloc] initWithLanguage:#"deu"];
t.delegate = self;
[t setVariableValue:#"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" forKey:#"tessedit_char_whitelist"];
[t setImage:img];
[t recognize];
NSLog( #"Recognized text: %#", [t recognizedText] );
labelRecognizedText.text = [t recognizedText];
t = nil;
The sample image from the project tempalte
works well (which tells me that the project itself is setup correctly), but whenever I try to use other images, the recognized text is a complete mess. For example, I tried to take a picture of my finder displaying the sample image:
https://dl.dropboxusercontent.com/u/607872/tesseract.jpg (1,5 MB)
But Tesseract recognizes:
Recognized text: s f l TO if v Ysssifss f
ssqxizg ss sfzzlj z
s N T IYIOGY Z I l EY s s
k Es ETL ZHE s UEY
z xhks Fsjs Es z VIII c
s I XFTZT c s h V Ijzs
L s sk sisijk J
s f s ssj Jss sssHss H VI
s s H
i s H st xzs
s s k 4 is x2 IV
Illlsiqss sssnsiisfjlisszxiij s
K
Even when the character whitelist only contains numbers, I don't get a result even close to what the image looks like:
Recognized text: 3 74 211
1
1 1 1
3 53 379 1
3 1 33 5 3 2
3 9 73
1 61 2 2
3 1 6 5 212 7
1
4 9 4
1 17
111 11 1 1 11 1 1 1 1
I assume there's something wrong with the way fotos are taken from the iPad mini's camera I currently use, but I can't figure out what and why.
Any hints?
Update #1
In response to Tomas:
I followed the tutorial in your post but encountered several errors along the way...
the UIImage+OpenCV category cannot be used in my ARC project
I cannot import <opencv2/...> in my controllers, auto-completion does not offer it (and therefore [UIImage CVMat] is not defined)
I think there's something wrong with my integration of OpenCV, even though I followed the Hello-tutorial and added the framework. Am I required to build OpenCV on my Mac as well or is it sufficient to just include the framework in my Xcode project?
Since I don't really know what you might consider as "important" at this point (I've already read several posts and tutorials and tried different steps), feel free to ask :)
Update #2
#Tomas: thanks, the ARC-part was essential. My ViewController already has been renamed to .mm. Forget the part about "cannot import opencv2/" since I already included it in my TestApp-Prefix.pch (as stated in the Hello-tutorial).
On to the next challenge ;)
I noticed that when I use images taken with the camera, the bounds for the roi object aren't calculated successfully. I played around with the device orientation and put a UIImage in my view to see the image processing steps, but sometimes (even when the image is correctly aligned) the values are negative because the if-condition in the bounds.size()-for-loop isn't met. The worst case I had: minX/Y and maxX/Y were never touched. Long story short: the line starting with Mat roi = inranged(cv::Rect( throws an exception (assertion failed because the values were < 0 ). I don't know if the number of contours matter, but I assume so because the bigger the images, the more likely the assertion exception is.
To be perfectly honest: I haven't had the time to read OpenCV's documentation and understand what your code does, but as of now, I don't think there's a way around. Seems like, unfortunately for me, my initial task (scan receipt, run OCR, show items in a table) requires more resources (=time) than I thought.
There's nothing wrong in the way your taking the pictures from your iPad per se. But you just can't throw in such a complex image and expect Tesseract to magically determine which text to extract. Take a closer look to the image and you'll notice it has no uniform lightning, it's extremely noisy so it may not be the best sample to start playing with.
In such scenarios it is mandatory to pre process the image in order to provide the tesseract library with something simpler to recognise.
Below find a very naive pre processing example that uses OpenCV (http://www.opencv.org), a popular image processing framework. It should give you and idea to get you started.
#import <TesseractOCR/TesseractOCR.h>
#import <opencv2/opencv.hpp>
#import "UIImage+OpenCV.h"
using namespace cv;
...
// load source image
UIImage *img = [UIImage imageNamed:#"tesseract.jpg"];
Mat mat = [img CVMat];
Mat hsv;
// convert to HSV (better than RGB for this task)
cvtColor(mat, hsv, CV_RGB2HSV_FULL);
// blur is slightly to reduce noise impact
const int blurRadius = img.size.width / 250;
blur(hsv, hsv, cv::Size(blurRadius, blurRadius));
// in range = extract pixels within a specified range
// here we work only on the V channel extracting pixels with 0 < V < 120
Mat inranged;
inRange(hsv, cv::Scalar(0, 0, 0), cv::Scalar(255, 255, 120), inranged);
Mat inrangedforcontours;
inranged.copyTo(inrangedforcontours); // findContours alters src mat
// now find contours to find where characters are approximately located
vector<vector<cv::Point> > contours;
vector<Vec4i> hierarchy;
findContours(inrangedforcontours, contours, hierarchy, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cv::Point(0, 0));
int minX = INT_MAX;
int minY = INT_MAX;
int maxX = 0;
int maxY = 0;
// find all contours that match expected character size
for (size_t i = 0; i < contours.size(); i++)
{
cv::Rect brect = cv::boundingRect(contours[i]);
float ratio = (float)brect.height / brect.width;
if (brect.height > 250 && ratio > 1.2 && ratio < 2.0)
{
minX = MIN(minX, brect.x);
minY = MIN(minY, brect.y);
maxX = MAX(maxX, brect.x + brect.width);
maxY = MAX(maxY, brect.y + brect.height);
}
}
// Now we know where our characters are located
// extract relevant part of the image adding a margin that enlarges area
const int margin = img.size.width / 50;
Mat roi = inranged(cv::Rect(minX - margin, minY - margin, maxX - minX + 2 * margin, maxY - minY + 2 * margin));
cvtColor(roi, roi, CV_GRAY2BGRA);
img = [UIImage imageWithCVMat:roi];
Tesseract *t = [[Tesseract alloc] initWithLanguage:#"eng"];
[t setVariableValue:#"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" forKey:#"tessedit_char_whitelist"];
[t setImage:img];
[t recognize];
NSString *recognizedText = [[t recognizedText] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
if ([recognizedText isEqualToString:#"1234567890"])
NSLog(#"Yeah!");
else
NSLog(#"Epic fail...");
Notes
The UIImage+OpenCV category can be found here. If you're under ARC check this.
Take a look at this to get you started with OpenCV in Xcode. Note that OpenCV is a C++ framework which can't be imported in plain C (or Objective-C) source files. The easiest workaround is to rename your view controller from .m to .mm (Objective-C++) and reimport it in your project.
There is different behavior of tesseract result.
It requires good quality of picture means good texture visibility.
Large size picture take much time to process its also good to resize it into small before processing.
It will good to perform some color effect on image before sending it to tesseract. Use effects which could enhance the visibility of image.
There is sometime different behavior of processing photo by using Camera or by Camera Album.
In case of taking photo directly from Camera try below function.
- (UIImage *) getImageForTexture:(UIImage *)src_img{
CGColorSpaceRef d_colorSpace = CGColorSpaceCreateDeviceRGB();
/*
* Note we specify 4 bytes per pixel here even though we ignore the
* alpha value; you can't specify 3 bytes per-pixel.
*/
size_t d_bytesPerRow = src_img.size.width * 4;
unsigned char * imgData = (unsigned char*)malloc(src_img.size.height*d_bytesPerRow);
CGContextRef context = CGBitmapContextCreate(imgData, src_img.size.width,
src_img.size.height,
8, d_bytesPerRow,
d_colorSpace,
kCGImageAlphaNoneSkipFirst);
UIGraphicsPushContext(context);
// These next two lines 'flip' the drawing so it doesn't appear upside-down.
CGContextTranslateCTM(context, 0.0, src_img.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// Use UIImage's drawInRect: instead of the CGContextDrawImage function, otherwise you'll have issues when the source image is in portrait orientation.
[src_img drawInRect:CGRectMake(0.0, 0.0, src_img.size.width, src_img.size.height)];
UIGraphicsPopContext();
/*
* At this point, we have the raw ARGB pixel data in the imgData buffer, so
* we can perform whatever image processing here.
*/
// After we've processed the raw data, turn it back into a UIImage instance.
CGImageRef new_img = CGBitmapContextCreateImage(context);
UIImage * convertedImage = [[UIImage alloc] initWithCGImage:
new_img];
CGImageRelease(new_img);
CGContextRelease(context);
CGColorSpaceRelease(d_colorSpace);
free(imgData);
return convertedImage;
}
I have been struggling with Tesseract character recognition for weeks. Here are two things I learned to get it to work better...
If you know what font you will be reading, clear the training and retrain it for only that font. Multiple fonts slows the OCR processing down and also increases the ambiguity in the Tesseract decision process. This will lead to greater accuracy and speed.
After OCR processing is really needed. You will end up with a matrix of characters that Tesseract recognizes. You will need to further process the characters to narrow down on what you are trying to read. So for instance, if your application is reading food labels, knowing the rules for the words and sentences that make up the food label will help recognize a series of characters that make up that label.
Convert your UIImage from srgb to rgb format .
if you are using IOS 5.0 and above use
use #import <Accelerate/Accelerate.h>
else uncomment //IOS 3.0-5.0
-(UIImage *) createARGBImageFromRGBAImage: (UIImage*)image
{ //CGSize size = CGSizeMake(320, 480);
CGSize dimensions = CGSizeMake(320, 480);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * dimensions.width;
NSUInteger bitsPerComponent = 8;
unsigned char *rgba = malloc(bytesPerPixel * dimensions.width * dimensions.height);
unsigned char *argb = malloc(bytesPerPixel * dimensions.width * dimensions.height);
CGColorSpaceRef colorSpace = NULL;
CGContextRef context = NULL;
colorSpace = CGColorSpaceCreateDeviceRGB();
context = CGBitmapContextCreate(rgba, dimensions.width, dimensions.height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault); // kCGBitmapByteOrder32Big
CGContextDrawImage(context, CGRectMake(0, 0, dimensions.width, dimensions.height), [image CGImage]);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
const vImage_Buffer src = { rgba, dimensions.height, dimensions.width, bytesPerRow };
const vImage_Buffer dis = { rgba, dimensions.height, dimensions.width, bytesPerRow };
const uint8_t map[4] = {3,0,1,2};
vImagePermuteChannels_ARGB8888(&src, &dis, map, kvImageNoFlags);
//IOS 3.0-5.0
/*for (int x = 0; x < dimensions.width; x++) {
for (int y = 0; y < dimensions.height; y++) {
NSUInteger offset = ((dimensions.width * y) + x) * bytesPerPixel;
argb[offset + 0] = rgba[offset + 3];
argb[offset + 1] = rgba[offset + 0];
argb[offset + 2] = rgba[offset + 1];
argb[offset + 3] = rgba[offset + 2];
}
}*/
colorSpace = CGColorSpaceCreateDeviceRGB();
context = CGBitmapContextCreate(dis.data, dimensions.width, dimensions.height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrderDefault); // kCGBitmapByteOrder32Big
CGImageRef imageRef = CGBitmapContextCreateImage(context);
image = [UIImage imageWithCGImage: imageRef];
CGImageRelease(imageRef);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(rgba);
free(argb);
return image;
}
Tesseract *t = [[Tesseract alloc] initWithLanguage:#"eng"];
[t setVariableValue:#"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" forKey:#"tessedit_char_whitelist"];
[t setImage:[self createARGBImageFromRGBAImage:img]];
[t recognize];
The swift equivalent of #FARAZ's answer
func getImageForTexture(srcImage: UIImage) -> UIImage{
let d_colorSpace = CGColorSpaceCreateDeviceRGB()
let d_bytesPerRow: size_t = Int(srcImage.size.width) * 4
/*
* Note we specify 4 bytes per pixel here even though we ignore the
* alpha value; you can't specify 3 bytes per-pixel.
*/
let imgData = malloc(Int(srcImage.size.height) * Int(d_bytesPerRow))
let context = CGBitmapContextCreate(imgData, Int(srcImage.size.width), Int(srcImage.size.height), 8, Int(d_bytesPerRow), d_colorSpace,CGImageAlphaInfo.NoneSkipFirst.rawValue)
UIGraphicsPushContext(context!)
// These next two lines 'flip' the drawing so it doesn't appear upside-down.
CGContextTranslateCTM(context, 0.0, srcImage.size.height)
CGContextScaleCTM(context, 1.0, -1.0)
// Use UIImage's drawInRect: instead of the CGContextDrawImage function, otherwise you'll
srcImage.drawInRect(CGRectMake(0.0, 0.0, srcImage.size.width, srcImage.size.height))
UIGraphicsPopContext()
/*
* At this point, we have the raw ARGB pixel data in the imgData buffer, so
* we can perform whatever image processing here.
*/
// After we've processed the raw data, turn it back into a UIImage instance.
let new_img = CGBitmapContextCreateImage(context)
let convertedImage = UIImage(CGImage: new_img!)
return convertedImage
}
I initialized the array like so
CGImageRef imageRef = CGImageCreateWithImageInRect(image.CGImage, bounds);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
unsigned char *rawData = malloc(height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
However, when I tried checking the count through an NSLog, I always get 4 (4/1, specifically).
int count = sizeof(rawData)/sizeof(rawData[0]);
NSLog(#"%d", count);
Yet when I NSLog the value of individual elements, it returns non zero values.
ex.
CGFloat f1 = rawData[15];
CGFloat f2 = rawData[n], where n is image width*height*4;
//I wasn't expecting this to work since the last element should be n-1
Finally, I tried
int n = lipBorder.size.width *lipBorder.size.height*4*2; //lipBorder holds the image's dimensions, I tried multiplying by 2 because there are 2 pixels for every CGPoint in retina
CGFloat f = rawData[n];
This would return different values each time for the same image, (ex. 0.000, 115.000, 38.000).
How do I determine the count / how are the values being stored into the array?
rawData is a pointer to unsigned char, as such its size is 32 bits (4 bytes)[1]. rawData[0] is an unsigned char, as such its size is 8 bits (1 byte). Hence, 4/1.
You've probably seen this done with arrays before, where it does work as you would expect:
unsigned char temp[10] = {0};
NSLog(#"%d", sizeof(temp)/sizeof(temp[0])); // Prints 10
Note, however, that you are dealing with a pointer to unsigned char, not an array of unsigned char - the semantics are different, hence why this doesn't work in your case.
If you want the size of your buffer, you'll be much better off simply using height * width * 4, since that's what you passed to malloc anyway. If you really must, you could divide that by sizeof(char) or sizeof(rawData[0]) to get the number of elements, but since they're chars you'll get the same number anyway.
Now, rawData is just a chunk of memory somewhere. There's other memory before and after it. So, if you attempt to do something like rawData[height * width * 4], what you're actually doing is attempting to access the next byte of memory after the chunk allocated for rawData. This is undefined behaviour, and can result in random garbage values being returned[2] (as you've observed), some "unassigned memory" marker value being returned, or a segmentation fault occurring.
[1]: iOS is a 32-bit platform
[2]: probably whatever value was put into that memory location last time it was legitimately used.
The pointer returned by malloc is a void* pointer meaning that it returns a pointer to an address in memory. It seems that the width and the height that are being returned are 0. This would explain why you are only being allocated 4 bytes for your array.
You also said that you tried
int n = lipBorder.size.width *lipBorder.size.height*4*2; //lipBorder holds the image's dimensions, I tried multiplying by 2 because there are 2 pixels for every CGPoint in retina
CGFloat f = rawData[n];
and were receiving different values each time. This behavior is to be expected given that your array is only 4 bytes long and you are accessing an area of memory that is much further ahead in memory. The reason that the value was changing was that you were accessing memory that was not in your array, but in a memory location that was
lipBorder.size.width *lipBorder.size.height*4*2 - 4 bytes passed the end of your array. C in no way prevent you from accessing any memory within your program. If you had accessed memory that is off limits to your program you would have received a segmentation fault.
You can therefore access n + 1 or n + 2 or n + whatever element. It only means that you are accessing memory that is passed the end of your array.
Incrementing the pointer rawdata would move the memory address by one byte. Incrementing and int pointer would increment move the memory address by 4 bytes (sizeof(int)).