How to get access to image pixels?

[TOMSOFT]

Just an update - for some reason the afastrunner's code works fine on the simulator but not on the actual device (the image is still coming through blue). Anyone had a similar experience when messing around with pixel data?

[ng93]

how would i get the image RGB values into a NSString?

i've tried:

for (int index = 0; index < length; index += 4) {
    NSString *string = [[NSString alloc] initWithString:[NSString stringWithFormat:@"RGB: %d, %d, %d",m_PixelBuf[index+1],m_PixelBuf[index+2],m_PixelBuf[index+3]]];
    m_PixelBuf[index + 1] = 255 - m_PixelBuf[index + 1];
    m_PixelBuf[index + 2] = 255 - m_PixelBuf[index + 2];
    m_PixelBuf[index + 3] = 255 - m_PixelBuf[index + 3];   
}

but it just says 255 for every value

cheers for any help
ng93

[rocotilos]

ng93, your code only will get the RGB values of last pixel of the image.
And I dont recommend putting the Alloc inside a loop. That just gonna eat up your memory.

[LaMarmotte]

Originally Posted by TOMSOFT

Just an update - for some reason the afastrunner's code works fine on the simulator but not on the actual device (the image is still coming through blue). Anyone had a similar experience when messing around with pixel data?

I am encountering the same issue, Did you manage to fix it?

Thanks

[markyD]

Originally Posted by LaMarmotte

I am encountering the same issue, Did you manage to fix it?

Thanks

Sorry for bring up an old issue but there are probably others that search these forums also.

The error is in the call to CGBitmapContextCreate(), the last argument should be the bitmap-info and not the alpha-info.
Just replace that line with:

	ctx = CGBitmapContextCreate(m_PixelBuf,  
				CGImageGetWidth( inImage ),  
				CGImageGetHeight( inImage ),  
				CGImageGetBitsPerComponent(inImage),
				CGImageGetBytesPerRow( inImage ),  
				CGImageGetColorSpace( inImage ),  
				CGImageGetBitmapInfo(inImage) );

--Mark

[rocotilos]

SPAMBOT DETECTED.

ADMIN, BRING THE RAIN!

(i always wanted to say that lol)

[abolfoooud2]

Hi

this is my first post here

have looked at this code and tried and it all works fine. But there is something that i dont understand and i hope you can explain it:

Why do i need to create a new bitmap context with CGBitmapContextCreate? Shouldn't creating a new UIImage with imageWithCGImage and the CGImageRef already created and manipulated at the beginning be sufficient? Why to duplicate the image and memory?


if i try the following i get a crash

        UIImage* img = [UIImage imageNamed:@"img.jpg"];	
        CGImageRef image = [img CGImage];
	CFDataRef dat = CGDataProviderCopyData(CGImageGetDataProvider(image));
	UInt8* data = (UInt8*)CFDataGetBytePtr(dat);
	
	for(int i=0; i<img.size.width*img.size.height*4; i+=4 )
	{
		data[i] = 255;
		data[i+1] = 255;
		data[i+2] = 0;
		data[i+3] = 0;
	}

        // removed the CGBitmapContextCreate code

	UIImage* rawImage = [UIImage imageWithCGImage:image]; 
	UIImageView *imgv = [[UIImageView alloc] initWithImage:rawImage];

Hope you can enlighten me
regs
AF

[wensi]

Originally Posted by TOMSOFT

Thanks afastrunner for providing the code. Its been really helpful.

If I comment out all your filter effects within your code and run the app the image comes out blue. Why is that? How do I recreate the original image without applying any effect (just so I know how the code works before I apply custom effects).

Thanks in advance.

you need something like this (last argument is kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big):

ctx = CGBitmapContextCreate(m_PixelBuf,  
                                CGImageGetWidth( inImage ),  
                                CGImageGetHeight( inImage ),  
                                8,  
                                CGImageGetBytesPerRow( inImage ),  
                                CGImageGetColorSpace( inImage ),  
                                kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );

[7twenty7]

Originally Posted by wensi

you need something like this (last argument is kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big):

Way to reply to a post that was almost 2.5 years old. I'm sure he appreciates your input.

[RoryHarvey]

Originally Posted by 7twenty7

Way to reply to a post that was almost 2.5 years old. I'm sure he appreciates your input.

Well I appreciated his input, seeing as this thread is indexed by something called 'Google'...

Anyway, the way to stop it coming out as blue is like so:

ctx = CGBitmapContextCreate(m_PixelBuf, 
                                CGImageGetWidth( inImage ), 
                                CGImageGetHeight( inImage ), 
                                8, 
                                CGImageGetBytesPerRow( inImage ), 
                                CGImageGetColorSpace( inImage ), 
                                kCGImageAlphaPremultipliedLast );

[RoryHarvey]

Originally Posted by yvmkpqzl43

Thanks for the quick answer. I've tried, but CoreGraphics is not present in my system?! I can see CoreAudio, Data, Foundation, Midi, Services, Video, but not Graphics?! How can that be???

You need to include

#include <ApplicationServices/ApplicationServices.h>