CODEWITHSUNDEEP
iosobjective-cimage-processingphotosframeworkvimage
Imran
Imran

Reputation: 1715

Issue in computing the histogram of an image using vImageHistogramCalculation

I have used vImageHistogramCalculation in my current application for calculating the histogram of image and I am getting EXC_BAD_ACCESS in some cases.I went through the cases as follows-

- (void)histogramForImage:(UIImage *)image {
    vImage_Buffer inBuffer;
    CGImageRef img = image.CGImage;

    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);

    inBuffer.width = CGImageGetWidth(img);
    inBuffer.height = CGImageGetHeight(img);
    inBuffer.rowBytes = CGImageGetBytesPerRow(img);

    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);

    vImagePixelCount histogram[4][8] = {{0}};
    vImagePixelCount *histogramPointers[4] = { &histogram[0][0], &histogram[1][0], &histogram[2][0], &histogram[3][0] };
    vImage_Error error = vImageHistogramCalculation_ARGBFFFF(&inBuffer, histogramPointers, 8, 0, 255, kvImageNoFlags);

    if (error) {
        NSLog(@"error %ld", error);
    }

    CGDataProviderRelease(inProvider);
}

  1. I used the image from iPhone Camera Roll in PNG form and manually put in bundle in the above code and it works fine.

  2. I used the same code for the image from iPhone Camera Roll in JPG format then I am getting EXC_BAD_ACCESS error.

  3. I tried to get image from Camera Roll using Photos Framework and then passed to the same code then also I am getting EXC_BAD_ACCESS error.

What I actually need is to find the histogram of all the images of iPhone Camera Roll.So I am unable to find out why the above code is working fine for one image format and failing for other.Is there any other reason for the crash?

EDIT 1- what I came to its not about image format its working fine for some JPG images too but still its crashing in some cases.How should I figure that out?

Reference:

https://developer.apple.com/library/mac/documentation/Performance/Reference/vImage_histogram/#//apple_ref/c/func/vImageHistogramCalculation_ARGBFFFF

Compute the histogram of an image using vImageHistogramCalculation

Upvotes: 0

Views: 207

Answers (1)

Ian Ollmann
Ian Ollmann

Reputation: 1592

vImageHistogramCalculation_ARGBFFFF is for four-channel floating-point data. Chances are extremely high that the data you are getting out of the data provider is RGB or RGBA 8-bit integer data. Check with the CGImageRef for the storage format of the image data.

If you want a specific data format out of a CGImageRef, you can call vImageBuffer_InitWithCGImage().

Upvotes: 1

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