Thanks Quincey,
I've now pulled a color profile from a CVPixelBuffer obtained from iterating
through video frames of a movie file which I can use when creating my
CGBitmapContext which I hadn't been doing before so I'm sure this will also
work going the other way.
What I'd like to be able to do is to compare profiles obtained this way with
what I think must be AVFoundation's equivalent e.g.:
AVVideoColorPropertiesKey : [
AVVideoColorPrimariesKey : AVVideoColorPrimaries_ITU_R_709_2,
AVVideoTransferFunctionKey :
AVVideoTransferFunction_ITU_R_709_2,
AVVideoYCbCrMatrixKey : AVVideoYCbCrMatrix_ITU_R_601_4
],
But the documentation is so poor, I do not understand what things like
AVVideoColorPrimaries_ITU_R_709_2 mean, Apple docs don't help and my duck duck
go searches haven't helped.
When I get info about a movie file in Finder some will include a color profile
name e.g.: HD (1-1-1)
If I get info for an image file created from a movie using
AVAssetImageGenerator then the profile name is: Composite NTSC. But I have no
idea how to get this information in code. CGColorSpaceCopyName doesn't work as
it is only returns a string from a CGColorSpace created with
CGColorSpaceCreateWithName.
What I'd like to know is, is the color profile of the image generated from an
imported movie the same as the color profile equivalent for the movie (see
AVFoundation color property keys above) I'm creating from individual frames? It
would be ideal if I could keep everything using the same profile color space in
my processing pipeline.
Kevin
On 19 Jan 2015, at 01:56, Quincey Morris <quinceymor...@rivergatesoftware.com>
wrote:
> On Jan 18, 2015, at 17:22 , Kevin Meaney <k...@yvs.eu.com> wrote:
>>
>> How can I make sure that the CGBitmapContext and CVPixelBuffer view the
>> pixel data in the same way from a color matching perspective?
>
> You can attach a color space to the pixel buffer as follows:
>
> CVBufferSetAttachment (pixelBuffer, kCVImageBufferCGColorSpaceKey, …,
> kCVAttachmentMode_ShouldNotPropagate);
>
> Depending on what you do next, I would expect the pixel buffer data to either
> be converted to a destination color space, or to have its color space
> propagated to the destination. (Note that the attachment mode “should not
> propagate” refers to something unrelated, AFAIK. But I’m not an expert on any
> of this.)
>
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