CODEWITHSUNDEEP
ios
SuperString
SuperString

Reputation: 22549

iOS: taking low quality image

I want to take allow the user to take a picture and then show the greyscale version. However, it is very slow because the image file is too big/resolution is too high.

How can I reduce the quality of the image when the user takes the picture?

Heres the code I am using for the transformation:

    - (UIImage *)convertImageToGrayScale:(UIImage *)image
{
    // Create image rectangle with current image width/height
    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);
    // Grayscale color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    // Create bitmap content with current image size and grayscale colorspace
    CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);
    // Draw image into current context, with specified rectangle
    // using previously defined context (with grayscale colorspace)
    CGContextDrawImage(context, imageRect, [image CGImage]);
    /* changes start here */
    // Create bitmap image info from pixel data in current context
    CGImageRef grayImage = CGBitmapContextCreateImage(context);
    // release the colorspace and graphics context
    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);
    // make a new alpha-only graphics context
    context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, nil, kCGImageAlphaOnly);
    // draw image into context with no colorspace
    CGContextDrawImage(context, imageRect, [image CGImage]);
    // create alpha bitmap mask from current context
    CGImageRef mask = CGBitmapContextCreateImage(context);
    // release graphics context
    CGContextRelease(context);
    // make UIImage from grayscale image with alpha mask
    UIImage *grayScaleImage = [UIImage imageWithCGImage:CGImageCreateWithMask(grayImage, mask) scale:image.scale orientation:image.imageOrientation];
    // release the CG images
    CGImageRelease(grayImage);
    CGImageRelease(mask);
    // return the new grayscale image
    return grayScaleImage;
    /* changes end here */
}

Upvotes: 3

Views: 1885

Answers (2)

Stavash
Stavash

Reputation: 14314

How about downsampling the UIImage before passing it on to the grayscale translation? Something like:

NSData *imageAsData = UIImageJPEGRepresentation(imageFromCamera, 0.5);
UIImage *downsampledImaged = [UIImage imageWithData:imageAsData];

You could use other compression qualities other than 0.5 of course.

Upvotes: 2

torrey.lyons
torrey.lyons

Reputation: 5589

If you are using AVFoundation to capture the image you can set the quality of the image to be captured by changing the capture session preset like the following:

AVCaptureSession *session = [[AVCaptureSession alloc] init];
session.sessionPreset = AVCaptureSessionPresetLow;

There is a table of which presents correspond to which resolution in the AVFoundation Programming Guide.

Upvotes: 2

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