I am downloading multiple images from below code and saving to the DB. But for some images I am getting below error.
Error: ImageIO: PNG invalid distance too far back
Error: ImageIO: PNG incorrect data check
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
NSString *imgStr = [dict objectForKey:#"image"];
imgStr = [imgStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSData *imgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:imgStr]];
UIImage *image = [UIImage imageWithData:imgData];
dispatch_sync(dispatch_get_main_queue(), ^{
mYImageView.image = image;
});
});
How to check stored image is valid or not, so I can download image again?
For PNG images, check their first two bytes and last two bytes. Below is the method, hope it helps.
Thanks. :)
- (BOOL)isImageValid:(NSData *)data
{
BOOL val = YES;
if ([data length] < 4)
val = NO;
const char * bytes = (const char *)[data bytes];
if (bytes[0] != 0x89 || bytes[1] != 0x50)
val = NO;
if (bytes[[data length] - 2] != 0x60 ||
bytes[[data length] - 1] != 0x82)
val = NO;
return val;
}
The accepted answer by swati sharma works great. Here’s a Swift extension for anyone looking to do the same in Swift:
extension Data
{
/// Returns whether or not the data is for a valid PNG file.
var isValidPNG: Bool
{
guard self.count > 4 else { return false }
return self[0] == 0x89 &&
self[1] == 0x50 &&
self[self.count - 2] == 0x60 &&
self[self.count - 1] == 0x82
}
}
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In server, the image is stored in binary format. I have to retrieve the image in iphone using json. How can I do that? Is it possible to do this using NSData also?
Yes, you need to covert binary data to NSData like this:
NSData *imgData = [NSData dataWithBase64EncodedString:yourelement];
UIImage *theImg = [UIImage imageWithData:imgData];
You would need MBBase64 class which is available here: https://github.com/jerrykrinock/CategoriesObjC
You have to get the binary value from the server using json parsing and then convert that string to NSData.
This is the standard code used for converting the base64 string to NSData.
//MBBase64.h
#interface NSData (MBBase64)
+ (id)dataWithBase64EncodedString:(NSString *)string; // Padding '=' characters are optional. Whitespace is ignored.
#end
//MBBase64.m
static const char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
#implementation NSData (MBBase64)
+ (id)dataWithBase64EncodedString:(NSString *)string;
{
if (string == nil)
[NSException raise:NSInvalidArgumentException format:nil];
if ([string length] == 0)
return [NSData data];
static char *decodingTable = NULL;
if (decodingTable == NULL)
{
decodingTable = malloc(256);
if (decodingTable == NULL)
return nil;
memset(decodingTable, CHAR_MAX, 256);
NSUInteger i;
for (i = 0; i < 64; i++)
decodingTable[(short)encodingTable[i]] = i;
}
const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
if (characters == NULL) // Not an ASCII string!
return nil;
char *bytes = malloc((([string length] + 3) / 4) * 3);
if (bytes == NULL)
return nil;
NSUInteger length = 0;
NSUInteger i = 0;
while (YES)
{
char buffer[4];
short bufferLength;
for (bufferLength = 0; bufferLength < 4; i++)
{
if (characters[i] == '\0')
break;
if (isspace(characters[i]) || characters[i] == '=')
continue;
buffer[bufferLength] = decodingTable[(short)characters[i]];
if (buffer[bufferLength++] == CHAR_MAX) // Illegal character!
{
free(bytes);
return nil;
}
}
if (bufferLength == 0)
break;
if (bufferLength == 1) // At least two characters are needed to produce one byte!
{
free(bytes);
return nil;
}
// Decode the characters in the buffer to bytes.
bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
if (bufferLength > 2)
bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
if (bufferLength > 3)
bytes[length++] = (buffer[2] << 6) | buffer[3];
}
realloc(bytes, length);
return [NSData dataWithBytesNoCopy:bytes length:length];
}
#end
Then load that resulted NSdata in UIimageview
yourimageview.image = [[UIImage alloc] initWithData:resultdata];
I am trying to receive a jpeg image from my c# server. The weird thing is when I run it with the debugger and have a break point anywhere in the method it works perfectly fine. Without a breakpoint then I get this error
Corrupt JPEG data: premature end of data segment
Here is my code
(void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode {
NSMutableData *data;
data = [NSMutableData new];
switch(eventCode) {
case NSStreamEventHasBytesAvailable:
{
uint8_t buffer[1024];
int len;
while([inputStream hasBytesAvailable]) {
len = [inputStream read:buffer maxLength:sizeof(buffer)];
if (len > 0)
{
[data appendBytes:(const void*)buffer length:sizeof(buffer)];
}
}
UIImage *images = [[UIImage alloc]initWithData:data];
[dvdCover setImage:images];
} break;
case NSStreamEventEndEncountered:
{
//UIImage *images = [[UIImage alloc]initWithData:data];
//[dvdCover setImage:images];
} break;
}
}
hi you can check this code hop it will help you...
case NSStreamEventHasBytesAvailable:
{
uint32_t max_size = 1000000; // Max size of the received imaged you can modify it as your reqirement.
NSMutableData* buffer = [[NSMutableData alloc] initWithLength: max_size];
NSInteger totalBytesRead = 0;
NSInteger bytesRead = [(NSInputStream *)stream read: [buffer mutableBytes] maxLength: max_size];
if (bytesRead != 0) {
while (bytesRead > 0 && totalBytesRead + bytesRead < max_size) {
totalBytesRead+= bytesRead;
bytesRead = [(NSInputStream *)stream read: [buffer mutableBytes] + totalBytesRead maxLength: max_size - totalBytesRead];
}
if (bytesRead >= 0) {
totalBytesRead += bytesRead;
}
else {
// read failure, report error and bail (not forgetting to release buffer)
}
[buffer setLength: totalBytesRead];
yourImageName.image = [UIImage imageWithData: buffer];
[buffer release];
} break;
It seems you are assuming the whole JPEG image will be transferred in one chunk, and you can just read it with one occurence of 'HasBytesAvailable' event. However you should also consider the case where the JPEG image is transferred to you in multiple chunks.
It might work for you if you set breakpoint, because your code execution might be halted somewhere, and your network buffer had plenty time to receive all bytes of the image. But without breakpoints it might not have time to do so.
Try refactoring your code to accumulate the bytes chunk, and only assume it's done when all bytes have been transferred. (Normally you have to know beforehand how many bytes the image is going to be -- or you can just capture the end of stream event)
I have looked everywhere and cannot find a solution to my problem. I have written a program for Android and Windows both that calculates the SHA1 hash of a given image. I confirmed these hashes with HashCalc that I downloaded. However when I try to do the same for iPhone I get a completely different hash. I believe it has something to do with converting the image to a byte array before I compute the hash. Here is my code:
- (void)imagePickerCotroller:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
UIImage *image = [info objectForKey:UIImagePickerControllerOriginalImage];
[imageview setImage:image];
NSData* imageData = UIImageJPEGRepresentation(image, 1);
NSString *hash = makeSHA1(imageData);
[filepath setText: hash];
[self dismissModalViewControllerAnimated:YES];
}
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
[self dismissModalViewControllerAnimated:YES];
}
NSString* makeSHA1(NSData *data) {
uint8_t digest[CC_SHA1_DIGEST_LENGTH];
CC_SHA1(data.bytes, data.length, digest);
NSMutableString* output = [NSMutableString stringWithCapacity:CC_SHA1_DIGEST_LENGTH * 2];
for(int i = 0; i < CC_SHA1_DIGEST_LENGTH; i++)
[output appendFormat:#"%02x", digest[i]];
return output;
}
I suspect the problem here is that you're converting the data using UIImageJPEGRepresentation(). Even if you started with JPEG data, there isn't a promise that this returns exactly the same bytes as you started with.
My (untested) suggestion is that you ask the CGDataProvider for the raw data. Something like this:
CGImageRef cgImage = [image CGImage];
CGDataProviderRef provider = CGImageGetDataProvider(cgImage);
CFDataRef imageData = CGDataProviderCopyData(provider);
if (imageData != NULL) {
...
CFRelease(imageData);
}
So I'm making an iOS app that constantly sends and array of points through NSStreams, but because sometimes the sender writes two arrays before the receiver receives one, I decided to first write the length, then the array data itself, so that the receiver knows how many bytes to process.
sender:
if (_outStream && [_outStream hasSpaceAvailable]){
const uint8_t *buffer = [data bytes];
uint64_t length = CFSwapInt64HostToLittle([data length]);
NSLog(#"Sending bytes with length: %llu", length);
int er1 = [_outStream write:(const uint8_t *)&length maxLength:sizeof(length)];
int er2 = [_outStream write:buffer maxLength:length];
if (er1 < 0 || er2 < 0) {
[self _showAlert:#"Failed sending data to peer"];
}
}
receiver:
case NSStreamEventHasBytesAvailable:
{
if (stream == _inStream) {
uint8_t *b;
int len = 0;
len = [_inStream read:b maxLength:8];
uint64_t dataLength = CFSwapInt64LittleToHost(*b);
NSLog(#"Received bytes with length: %llu", dataLength);
if(len < 0) {
if ([stream streamStatus] != NSStreamStatusAtEnd)
[self _showAlert:#"Failed reading data from peer"];
} else if (len > 0){
uint8_t bytes[dataLength];
int length = [_inStream read:bytes maxLength:dataLength];
[currentDownload appendBytes:bytes length:length];
id pointsArray = [NSKeyedUnarchiver unarchiveObjectWithData:currentDownload];
[currentDownload release];
currentDownload = [[NSMutableData alloc] init];
if ([pointsArray isKindOfClass:[NSArray class]]) {
[drawScene addNewPoint:[[pointsArray objectAtIndex:0] CGPointValue] previousPoint:[[pointsArray objectAtIndex:1] CGPointValue]];
}
}
}
break;
}
The problem is that the receiver receives an incorrect integer, hence it reads an incorrect amount of bytes.
Can anyone help me with this?
Could it be that when you read the data, you're starting with the introductory bits intended to convey length, rather than starting with the actual data?
For:
[currentDownload appendBytes:bytes length:length];
try substituting something like this:
NSRange rangeLeftover = NSMakeRange(sizeof(uint8_t), [currentDownload length] - sizeof(uint8_t));
NSData *dataLeftover = [currentDownload subdataWithRange:rangeLeftover];
uint8_t bytesLeftover[[dataLeftover length]];
[dataLeftover getBytes:&bytesLeftover length:[dataLeftover length]];
currentDownload = [NSMutableData data]; // clear
[currentDownload appendBytes:bytesLeftover length:[dataLeftover length]];
I'm consuming a web service in my iPhone app. The web service method returns a response which has several fields (eg. ID, Description, etc..). One of these fields contains binary image data which I need to convert to UIImage in my iPhone application.
I'm using a NSXMLParser successfully to extract data from the XML response. In the parser:foundCharacters: selector of the XMLParser, it gives a NSString* pointing to the string within each field. Since this is a string, this is what I do to read image data when i encounter the image field:
UIImage *img = [[UIImage alloc] initWithData:[string dataUsingEncoding:NSUTF8StringEncoding]];
But img variable is still "nil" after this line. Seems like the data from XML string is not compatible with conversion. What am I doing wrong here? (I'm capable of reading other fields into my variables but not this image data field)
Thanks in advance..
Following fbrereto's answer, I managed to convert the string into NSData using a code sample at this link: http://www.cocoadev.com/index.pl?BaseSixtyFour (scroll to the code sample by MiloBird user). Now I can construct the image successfully.
It uses objective-c categories to add the selector + (id)dataWithBase64EncodedString:(NSString *)string; to the NSData class. Here's the necessary code sample I extracted from the above link:
//MBBase64.h
#interface NSData (MBBase64)
+ (id)dataWithBase64EncodedString:(NSString *)string; // Padding '=' characters are optional. Whitespace is ignored.
#end
//MBBase64.m
static const char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
#implementation NSData (MBBase64)
+ (id)dataWithBase64EncodedString:(NSString *)string;
{
if (string == nil)
[NSException raise:NSInvalidArgumentException format:nil];
if ([string length] == 0)
return [NSData data];
static char *decodingTable = NULL;
if (decodingTable == NULL)
{
decodingTable = malloc(256);
if (decodingTable == NULL)
return nil;
memset(decodingTable, CHAR_MAX, 256);
NSUInteger i;
for (i = 0; i < 64; i++)
decodingTable[(short)encodingTable[i]] = i;
}
const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
if (characters == NULL) // Not an ASCII string!
return nil;
char *bytes = malloc((([string length] + 3) / 4) * 3);
if (bytes == NULL)
return nil;
NSUInteger length = 0;
NSUInteger i = 0;
while (YES)
{
char buffer[4];
short bufferLength;
for (bufferLength = 0; bufferLength < 4; i++)
{
if (characters[i] == '\0')
break;
if (isspace(characters[i]) || characters[i] == '=')
continue;
buffer[bufferLength] = decodingTable[(short)characters[i]];
if (buffer[bufferLength++] == CHAR_MAX) // Illegal character!
{
free(bytes);
return nil;
}
}
if (bufferLength == 0)
break;
if (bufferLength == 1) // At least two characters are needed to produce one byte!
{
free(bytes);
return nil;
}
// Decode the characters in the buffer to bytes.
bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
if (bufferLength > 2)
bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
if (bufferLength > 3)
bytes[length++] = (buffer[2] << 6) | buffer[3];
}
realloc(bytes, length);
return [NSData dataWithBytesNoCopy:bytes length:length];
}
#end
Thank you all!
The trick with NSString is that there is an implicit encoding associated with the data it contains. The image you are receiving, however, is likely in a format that will not convert properly, as it is either binary data or some lossless encoding of binary data (e.g., base64). The trick, then, is to make sure you don't let NSString perform any encoding conversions at all, otherwise your image data will be corrupted. Instead of using dataUsingEncoding: I would try an API more like getBytes:maxLength:usedLength:encoding:options:range:remainingRange. While more complex than dataUsingEncoding: I think it'll give you the flexibility you need to get just the data from the NSString and nothing more.