PDFPage initWithImage: strange behavior

I can't understand the difference. It seams to be the same but is not!

Does enybody know why?

// Working:
PDFPage *imagePDFPage = [[PDFPage alloc] initWithImage:
[[NSImage alloc]initWithContentsOfFile:imagePath]];


// NOT W开发者_JAVA百科orking:
NSImage *image = [[NSImage alloc]initWithContentsOfFile:imagePath];                           
PDFPage *imagePDFPage = [[PDFPage alloc] initWithImage:image];

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Here's the solution:

NSImage *image = [[NSImage alloc]initWithContentsOfFile:imagePath]; 
PDFPage *imagePDFPage = [[PDFPage alloc] initWithImage:(CIImage *) image];