ESC POS print image issue - objective-c

Question

I am working on ESC POS printer. Using below code I am able to print the image, but the issue is an image not printing properly. You can see in the below image. Please review my code and let me know where exactly the issue.
- (void) btnPrintPicture{
UIImage * img = [UIImage imageNamed:#"download.png"];
int width = img.size.width;
int height = img.size.height;
unsigned char * binaryImageData = malloc(width * height);
unsigned char * data = malloc(height * (8 + width / 8));
unsigned char * grayData = [self convertImageToGray:img];
format_K_threshold(grayData, width, height, binaryImageData);
eachLinePixToCmd(binaryImageData, width, height, 0, data);
NSMutableArray *dataArray = [NSMutableArray new];
int splitBytes = 100;
NSData *comData = [[NSData alloc] initWithBytes:(const void *)data length:(height * (8+width/8))];
for(int i = 0; i < comData.length ; i=i+splitBytes){
NSData *subData = nil;
if((i+splitBytes)>comData.length){
subData = [comData subdataWithRange:NSMakeRange(i, (comData.length-i))];
}else{
subData = [comData subdataWithRange:NSMakeRange(i, splitBytes)];
}
[dataArray addObject:subData];
}
[dataArray enumerateObjectsUsingBlock:^(NSData *obj, NSUInteger idx, BOOL * _Nonnull stop) {
[self.discoveredPeripheral writeValue:obj forCharacteristic:self.discoveredCharacteristic type:CBCharacteristicWriteWithResponse];
}];
free(grayData);
free(binaryImageData);
free(data);
}
This method is used for converting image to grayscale.
-(unsigned char *)convertImageToGray:(UIImage *)i
{
int kRed = 1;
int kGreen = 2;
int kBlue = 4;
int colors = kGreen | kBlue | kRed;
int m_width = i.size.width;
int m_height = i.size.height;
uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(rgbImage, m_width, m_height, 8, m_width * 4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextSetShouldAntialias(context, NO);
CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [i CGImage]);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
// now convert to grayscale
uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height);
for(int y = 0; y < m_height; y++) {
for(int x = 0; x < m_width; x++) {
uint32_t rgbPixel=rgbImage[y*m_width+x];
uint32_t sum=0,count=0;
if (colors & kRed) {sum += (rgbPixel>>24)&255; count++;}
if (colors & kGreen) {sum += (rgbPixel>>16)&255; count++;}
if (colors & kBlue) {sum += (rgbPixel>>8)&255; count++;}
m_imageData[y*m_width+x]=sum/count;
}
}
free(rgbImage);
return m_imageData;}
void format_K_threshold(unsigned char * orgpixels, int xsize, int ysize, unsigned char * despixels) {
int graytotal = 0;
int k = 0;
int i;
int j;
int gray;
for(i = 0; i < ysize; ++i) {
for(j = 0; j < xsize; ++j) {
gray = orgpixels[k] & 255;
graytotal += gray;
++k;
}
}
int grayave = graytotal / ysize / xsize;
k = 0;
for(i = 0; i < ysize; ++i) {
for(j = 0; j < xsize; ++j) {
gray = orgpixels[k] & 255;
if(gray > grayave) {
despixels[k] = 0;
} else {
despixels[k] = 1;
}
++k;
}
}
}
This method is using ESC commands to print the image.
void eachLinePixToCmd(unsigned char * src, int nWidth, int nHeight, int nMode, unsigned char * data) {
int p0[] = { 0, 0x80 };
int p1[] = { 0, 0x40 };
int p2[] = { 0, 0x20 };
int p3[] = { 0, 0x10 };
int p4[] = { 0, 0x08 };
int p5[] = { 0, 0x04 };
int p6[] = { 0, 0x02 };
int nBytesPerLine = nWidth / 8;
int offset = 0;
int k = 0;
for (int i = 0; i < nHeight; i++) {
offset = i * (8 + nBytesPerLine);
data[offset + 0] = 0x1d;
data[offset + 1] = 0x76;
data[offset + 2] = 0x30;
data[offset + 3] = (unsigned char) (nMode & 0x01);
data[offset + 4] = (unsigned char) (nBytesPerLine % 0xff);
data[offset + 5] = (unsigned char) (nBytesPerLine / 0xff);
data[offset + 6] = 0x01;
data[offset + 7] = 0x00;
for (int j = 0; j < nBytesPerLine; j++) {
data[offset + 8 + j] = (unsigned char) (p0[src[k]] + p1[src[k + 1]] + p2[src[k + 2]] + p3[src[k + 3]] + p4[src[k + 4]] + p5[src[k + 5]] + p6[src[k + 6]] + src[k + 7]);
k = k + 8;
}
}
}
Thanks in advance.

Answer 1

Based on having fixed a very similar bug in a different project with this change, I am guessing that your image width is not divisible by 8.
This line will drop nWidth % 8 pixels on each row, causing a rightward slant if the image width is not divisible by 8.
int nBytesPerLine = nWidth / 8;
Instead, you should be padding with zeroes:
int nBytesPerLine = (nWidth + 7) / 8;
Your data variable needs to grow to match as well, it has the same issue.
Lastly, you are issuing the GS v 0 command for each row, which is not very efficient. You can issue this once for the entire image, and specify the height. From the same project, a C example is here.