Images of smaller page size PDF are not autoresized to full screen in iOS6

Question

I am trying to capture images from PDF and display them in my iPad application in a UIScrollView. App render the images to fullscreen (full size) when pdf page size is 1024 x 768 (standard 4:3 aspect ratio). But when the pdf page is of size 720 x 540 (same 4:3 aspect ratio but with less dimensions) I am seeing white border around the image. Below is the code snippet that i tried to capture the images.

CGPDFPageRef thePDFPageRef = CGPDFDocumentGetPage(pdfDocRef, pdfIterator);
CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB(); // RGB color space

        CGBitmapInfo bmi = (kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
        thumbnailWidth = 1024;
        thumbnailHeight = 768;
        CGContextRef context = CGBitmapContextCreate(NULL, thumbnailWidth, thumbnailHeight, 8, 0, rgb, bmi);


        if (context != NULL) // Must have a valid custom CGBitmap context to draw into
        {
            CGRect thumbRect = CGRectMake(0.0f, 0.0f, thumbnailWidth, thumbnailHeight); // Target thumb rect

            CGContextSetRGBFillColor(context, 1.0f, 1.0f, 1.0f, 1.0f);

            CGContextFillRect(context, thumbRect); // White fill

            CGContextConcatCTM(context, CGPDFPageGetDrawingTransform(thePDFPageRef, kCGPDFCropBox, thumbRect, 0, true)); // Fit rect

            CGContextSetRenderingIntent(context, kCGRenderingIntentDefault);
            CGContextSetInterpolationQuality(context, kCGInterpolationHigh);

            CGContextDrawPDFPage(context, thePDFPageRef); // Render the PDF page into the custom CGBitmap context

            imageRef = CGBitmapContextCreateImage(context); // Create CGImage from custom CGBitmap context

            CGContextRelease(context); // Release custom CGBitmap context reference
        }

        CGColorSpaceRelease(rgb); // Release device RGB color space reference

        CGPDFPageRelease(thePDFPageRef);
    }


    UIImage *image = [UIImage imageWithCGImage:imageRef scale:scale orientation:0];

How can I auto scale to full screen even when pdf page size is smaller?

Answer 1

I found the solution as below with scaling to rectangle.

(1) Get PDF page rectangle using

CGRect pageRect = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);

(2) Do scale the rectangle and apply transform to Identity Matrix

CGAffineTransform trans = CGAffineTransformIdentity;
trans = CGAffineTransformTranslate(trans, 0, pageRect.size.height);
trans = CGAffineTransformScale(trans, 1.0, -1.0);
rect = CGRectApplyAffineTransform(rect, trans);

(3) Use kCGPDFMediaBox instead of kCGPDFCropBox to avoid cropping of pdfs when size is different than standard.