And what I wrote is here: https://github.com/SheffieldKevin/attributesforpreset/blob/master/attributesforpreset/output.txt
Sent from my iPad > On 20 Jan 2015, at 01:39, Kevin Meaney <k...@yvs.eu.com> wrote: > > Forgot to mention. I wrote a little something a few days ago that iterates > through the export presets and prints out the audio and video settings. > > It uses a private Apple API so it's not for production code but the output is > useful to look at. It was the output from this command line tool that led me > to the Wikipedia pages. > > Kevin > > Sent from my iPad > >> On 19 Jan 2015, at 17:53, Quincey Morris >> <quinceymor...@rivergatesoftware.com> wrote: >> >>> On Jan 19, 2015, at 04:02 , Kevin Meaney <k...@yvs.eu.com> wrote: >>> >>> 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. >> >> Yes, this sucks, but it’s not quite Apple’s fault. This area (colorspaces) >> is a morass of disconnected information, and you have no real alternative to >> putting it together yourself. Each information source has different >> assumptions about your prior knowledge, your intentions and your workflow, >> and so doesn’t bother to connect its information to anything else. In many >> cases, you can’t even tell for sure which *direction* data is moving, let >> alone what’s happening to it. >> >> Wikipedia is a good place to start. “ITU_R_709_2” refers to ITU Rec. BT-709: >> >> http://en.wikipedia.org/wiki/Rec._709 >> >> “ITU_R_601” is ITU Rec. BT-601: >> >> http://en.wikipedia.org/wiki/Rec._601 >> >> These are broadcast TV standards, and therefore (of course) integral to >> movie-making, because … kittens. 709 is HD, 601 is SD. Color primaries are a >> way of describing a color space, so (in combination with information from >> another color space) can be used to derive a method of converting from one >> color space to another. Transfer functions and matrixes are each an entire >> method of converting HD or SD colors to RGB. (RGB in what colorspace? Beats >> me. Just RGB, because … fluffy kittens.) >> >>> 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. >> >> Because different color space names may imply different underlying color >> space conversion technologies, about all a mere mortal can do is compare >> names. However, I’m not sure what “keep” means in that last sentence. If you >> have an input image file, it already has a color space (explicit or >> implied). Your output movie has a color space that you specified when you >> started. If they don’t match, there’s nothing you can do to “keep” them the >> same, you simply have to do a conversion. >> >> It’s the AVAssetWriter’s job to make the conversion for you. The point is >> you don’t *want* to deal with anything beyond that. >> >> “It’s kittens all the way down.” >> _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
