[Sorry for the length, but I've tried to include as much detail as
necessary in order to get the best answer.)
My program captures images from a digital camera. Said camera is
*always* oriented in a portrait fashion, and the image is created by
the camera (as a JPEG) with the appropriate EXIF meta-data that
reflects this fact (orientation = 8).
My client has some old hardware that doesn't understand (more
accurately, doesn't even look at) the meta-data of the image, and
chokes on image files that aren't "normalized" (orientation = 1). So
my task is to re-orient the images so this hardware doesn't choke, but
also fixes the meta-data so that all data remain consistent (so that
programs that DO respect the meta-data will still work with the image
correctly).
Why, on a platform known for its graphics-handling capabilities, is
this so frickin' hard?! :)
A pristine JPEG downloaded from the camera has a wealth of information
stored in meta-data; specifically, when viewed in Preview.app, the
"More Info" pane has 5 tabs (GPS, General, Canon, Exif, TIFF), with a
total of 53 properties, NOT including the GPS info.
In order to rotate the image and fix the orientation meta-data, I've
tried several variations and permutations of:
1. Create an NSImage from the file;
2. Create a CGImageSourceRef from the file;
3. Create a CGImageSourceRef from the NSImage's TIFFRepresentation data;
4. Rotate the image;
5. Write out the file with a CGImageDestination thingie
The best I've managed to do in the way of preserving the meta-data was
a sequence of 1, 4, 3, 5. When I look at the resulting image in
Preview.app, a vast majority of the meta-data is gone, gone, gone: a
grand total of 16 properties in categories General, JFIF, Exif, and
TIFF. The greatest loss is nearly all the Exif data, which includes
such important information as date/time captured, exposure, ISO,
shutter speed, gamma, etc. From the original 34 Exif properties, all
I'm left with is Pixel X|Y Dimentions! Even looking at the properties
of the CGImage after completing step (3), that's all there is. AND,
if I omit the rotation step, the resulting CGImage "orientation"
property is still set to 1 (which I know to be an outright lie). WTF?!
I'm about to resort to using a third-part solution (jpegtran and
jpegexiforient) that I've found, but Shirley, I must be missing
something in the Cocoa/Carbon/Foundation/whatever frameworks that
would make my life a lot simpler. Am I right? Or is image
manipulation on the Mac really this difficult for programmers?
(Note: NO PART of this particular process involves actually
*displaying* the image; that comes later, and will involve the already-
processed image file.)
Thanks for sticking with me this far, and thanks in advance for any
help!
randy
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