CGBitmapContextCreate returns NULL for some pixels of width and height

Question

I have the following code to create a new bitmap graphics context.

NSLog(@"newRect Width %f",newRect.size.width);
NSLog(@"newRect Height %f",newRect.size.height);
NSLog(@"imageRef %@",imageRef);

CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                            newRect.size.width,
                                            newRect.size.height,
                                            CGImageGetBitsPerComponent(imageRef),
                                            0,
                                            CGImageGetColorSpace(imageRef),
                                            CGImageGetBitmapInfo(imageRef));

The newRect.size.width is the result of dividing the original width of UIImage by 2. The newRect.size.height is the result of dividing the original height of UIImage by 2.

But for some UIImages with sizes {3000, 2002},{3024, 4032},{4032, 3024} are okay and returning bitmap context.

But for some UIImages with sizes {1242, 2208}. Normally these are screenshots from my devices and returning NULL value.

. .

Is anyone can help on my issue. Thanks.

try to change your width, height with CGImageGetWidth(imageRef) and CGImageGetHeight(imageRef) — Quoc Nguyen, Mar 26 '18 at 07:52
@QuocNguyen Could you please explain more in details? I don't get what you want me to do. Thanks for your ans. — Nyein Ei Ei Tun, Mar 26 '18 at 08:10
try this CGContextRef bitmap = CGBitmapContextCreate(NULL, CGImageGetWidth(imageRef) , CGImageGetHeight(imageRef), CGImageGetBitsPerComponent(imageRef), 0, CGImageGetColorSpace(imageRef), CGImageGetBitmapInfo(imageRef)); — Quoc Nguyen, Mar 26 '18 at 08:12
@QuocNguyen still got the same issue "[Unknown process name] CGBitmapContextCreate: unsupported parameter combination: set CGBITMAP_CONTEXT_LOG_ERRORS environmental variable to see the details" — Nyein Ei Ei Tun, Mar 26 '18 at 08:21

Dmytro Trofymenko · Accepted Answer · 2018-03-26T09:12:14.150

I was not able to reproduce the problem. I would suggest to log all incoming parameters and append log to your question. Also look into console log, CGBitmapContextCreate may write something there that may give the insight about the problem.

UPDATED:

The problem you are facing has nothing to do with image size, but with combination of bitmap info/colorspace and bits per component. Here what I got in system log trying to create bitmap context with info you provided:

CGBitmapContextCreate: unsupported parameter combination:
    16 bits/component; integer;
    64 bits/pixel;
    RGB color space model; kCGImageAlphaLast;
    kCGImageByteOrder16Little byte order;
    4992 bytes/row.
Valid parameters for RGB color space model are:
    16  bits per pixel,      5  bits per component,      kCGImageAlphaNoneSkipFirst
    32  bits per pixel,      8  bits per component,      kCGImageAlphaNoneSkipFirst
    32  bits per pixel,      8  bits per component,      kCGImageAlphaNoneSkipLast
    32  bits per pixel,      8  bits per component,      kCGImageAlphaPremultipliedFirst
    32  bits per pixel,      8  bits per component,      kCGImageAlphaPremultipliedLast
    64  bits per pixel,      16 bits per component,      kCGImageAlphaPremultipliedLast
    64  bits per pixel,      16 bits per component,      kCGImageAlphaNoneSkipLast
    64  bits per pixel,      16 bits per component,      kCGImageAlphaPremultipliedLast|kCGBitmapFloatComponents
    64  bits per pixel,      16 bits per component,      kCGImageAlphaNoneSkipLast|kCGBitmapFloatComponents
    128 bits per pixel,      32 bits per component,      kCGImageAlphaPremultipliedLast|kCGBitmapFloatComponents
    128 bits per pixel,      32 bits per component,      kCGImageAlphaNoneSkipLast|kCGBitmapFloatComponents
See Quartz 2D Programming Guide (available online) for more information.

You can try to use something standard always or in case of failure, e.g.

CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                            newRect.size.width,
                                            newRect.size.height,
                                            8,
                                            0,
                                            CGColorSpaceCreateDeviceRGB(),
                                            kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host));

Or let system choose appropriate context for you:

   UIGraphicsBeginImageContextWithOptions(newRect.size, false, 1.0);
   CGContextRef bitmap = UIGraphicsGetCurrentContext();

   // Do your drawing here

   UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

Thanks for your ans and please check the edited question for more information. — Nyein Ei Ei Tun, Mar 26 '18 at 08:40
You are awesome. Both of your answer works for me. Thanks. If you don't mind, can you please share a way to print out the logs for CGBitmapContextCreate. Thanks again for your answer. — Nyein Ei Ei Tun, Mar 27 '18 at 06:33
@NyeinEiEiTun To enable logs you can try this way https://stackoverflow.com/questions/39496435/how-to-set-cgbitmap-context-log-errors-environmental-variable — Dmytro Trofymenko, Mar 27 '18 at 07:25

CGBitmapContextCreate returns NULL for some pixels of width and height

1 Answers1