Finder 'Get Info' Command shows Color Profiles

It is possible to show the color profile for a media file using the Finder Get Info command. Simply select a file in the Finder, then choose File -> Get Info. In the "More Info:" section you will see the color profile information.

Add Color Profile Automator Action Makes it Easy to Tag Video Content

There is an Add Color Profile Automator Action that can add an ‘nclc’ color tag to existing QuickTime movies.

You can use the Add Color Profile Automator Action to create an Automator Workflow to add an ‘nclc’ color tag to existing QuickTime movies.

It is very easy to setup an Automator Workflow using Automator. That is especially important for old content that is untagged, content that is coming from an external source, or anything else that is incorrectly tagged.

For information on using the Automator application to create an Automator Workflow, choose Help in Automator or Help > Mac Help in the Finder and search for “Automator”. For information on creating Automator actions, see Automator Programming Guide and Automator Framework Reference.

Media Creation & Editing

When working with AV Foundation, the AVAssetWriter object is used to write or transcode media data to a new file of a specified audiovisual container type. You should always explicitly specify the desired output colorspace using the AVVideoColorPropertiesKey dictionary. AV Foundation will automatically provide a color-match converting every pixel from the source color space to the destination color space.

Here's code to specify the video color space when writing media with AVAssetWriter:

Listing 1  Specifying the video color space when writing media with AVAssetWriter.

#import <Foundation/Foundation.h>

#import <AVFoundation/AVFoundation.h>

NSMutableDictionary *compressionSettings = NULL;

compressionSettings = [NSMutableDictionary dictionary];

/*

Specify the HD output color space for the video color properties

key (AVVideoColorPropertiesKey). During export, AV Foundation

will perform a color match from the input color space to the HD

output color space.

(If you require SD colorimetry, use AVVideoColorPrimaries_SMPTE_C,

AVVideoTransferFunction_ITU_R_709_2, and AVVideoYCbCrMatrix_ITU_R_601_4.)

 */

[compressionSettings setObject:AVVideoColorPrimaries_ITU_R_709_2

          forKey:AVVideoColorPrimariesKey];

[compressionSettings setObject:AVVideoTransferFunction_ITU_R_709_2

          forKey:AVVideoTransferFunctionKey];

[compressionSettings setObject:AVVideoYCbCrMatrix_ITU_R_709_2

          forKey:AVVideoYCbCrMatrixKey];

/* Create settings for encoding the media. */

NSDictionary* videoOutputSettings = [NSDictionary dictionaryWithObjectsAndKeys:AVVideoCodecH264, AVVideoCodecKey,

                                     AVVideoScalingModeResize, AVVideoScalingModeKey,

                                     [NSNumber numberWithInt:1280], AVVideoWidthKey,

                                     [NSNumber numberWithInt:720], AVVideoHeightKey,

                                     compressionSettings, AVVideoColorPropertiesKey,

                                     nil];

/* Create new input to receive sample buffers for writing to the output file. */

AVAssetWriterInput* videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoOutputSettings];

AVAssetWriter *assetWriter = <#Your AVAssetWriter object#>;

[assetWriter addInput:videoInput];

/* ...begin writing your media */

BOOL success = [assetWriter startWriting];

...

An AVAssetExportSession object can also be used to write or transcode media data to create a new file of the type described by one of the exporter presets. For example, you can create a movie for use on the iPod, iPhone or Apple TV. To create a movie for use on one of these devices, specify the desired device exporter using the available export presets (AVAssetExportPresetAppleM4VAppleTV, AVAssetExportPresetAppleM4ViPod, and so on). See the AVAssetExportSession Class Reference for more information. See also the Sample Code 'avexporter' and Sample Code 'avmetadataeditor' for an example of how to use the AVAssetExportSession class.

These exporters all perform a colorimetrically correct export when converting between different color spaces. This means if there's a color space conversion, the video is properly tagged with the 'nclc' tag.

When working with QTKit, you can use the QTKit writeToFile: withAttributes: method to export a QTMovie object for use on iPod, iPhone or Apple TV. The QTKit exporters for iPod, iPhone or Apple TV all perform a colorimetrically correct export when converting between HD and SD (in either direction). This means if there's a color space conversion not only is the appropriate transformation used, but the video is properly tagged as well.

For example, if you have Rec. 709 HD source content that you would like to export to Apple TV, the Apple TV exporter's color management will preserve your source correctly -- no conversion is necessary. Similarly, if you export that same source content to iPod or iPhone, a conversion from HD to SD is performed and the color values are adjusted accordingly.

See Technical Note TN2188 Exporting Movies for iPod, Apple TV and iPhone Listing 4 for a code snippet showing how to use QTKit to export to iPhone.

Working With Core Image

When using Core Image along with QuickTime and Visual Contexts you can also set the output color space for the CIContext using the kCIContextOutputColorSpace key. Core Image will then perform any required color-matching between the colorspace specified by the pixel buffer's CGColorspace and the kCIContextOutputColorSpace key (and working colorspace, too).

Capture from Camera

Currently, when you capture from the screen with AV Foundation there is an automatic color conversion to the HD color space. If you capture from the camera, the camera driver assigns a color tag to the captured frames that describes the color space of the camera.

If you use the AVCaptureMovieFileOutput method to save frames captured from the screen to a file, these will be automatically tagged with a HD color profile, and frames captured from the camera will be tagged by the camera driver with a color profile that describes the color space of the camera.

The QTKit Capture architecture will query the camera to determine what color space it is using, and make sure that the 'nclc' information is used all the way through the capture pipeline. This ensures that previews to the display are correct, as well as any compression and export operations using the device exporters, with the resulting movie tagged appropriately.