On an iOS 18 phone, I use AVCaptureSession to capture HDR with x420 format. The output CMSampleBuffer is HLG colorspace, the propagated attachments contain kCVImageBufferAmbientViewingEnvironmentKey and kCVImageBufferSceneIlluminationKey. Now I use CAMetalLayer to render the CVPixelBuffer to the screen, but the brightness is brighter than AVSampleBufferDisplayLayer.
Here is my code.
- (void)_updateColorSpaceIfNeed:(CVPixelBufferRef)pixelBuffer {
CAMetalLayer *layer = (CAMetalLayer *)_mtkView.layer;
if (![layer isKindOfClass:CAMetalLayer.class]) return;
layer.wantsExtendedDynamicRangeContent = YES;
CFDataRef ambientViewingEnvironment = (CFDataRef)CVBufferCopyAttachment(pixelBuffer, kCVImageBufferAmbientViewingEnvironmentKey, NULL);
NSData *data = (__bridge NSData *)ambientViewingEnvironment;
if (ambientViewingEnvironment) CFRelease(ambientViewingEnvironment);
CAEDRMetadata *metadata = [CAEDRMetadata HLGMetadataWithAmbientViewingEnvironment:data];
// CAEDRMetadata *metadata = [CAEDRMetadata HLGMetadata];
layer.EDRMetadata = metadata;
layer.pixelFormat = MTLPixelFormatRGBA16Float;
CGColorSpaceRef colorspace = CGColorSpaceCreateWithName(kCGColorSpaceITUR_2100_HLG);
layer.colorspace = colorspace;
if (colorspace) CGColorSpaceRelease(colorspace);
}
Why does the CAEDRMetadata class have "HLGMetadataWithAmbientViewingEnvironment:" and "HLGMetadata" methods, but does not provide the "HLGMetadataWithAmbientViewingEnvironment:sceneIllumination" method?
I want to know how kCVImageBufferAmbientViewingEnvironmentKey and kCVImageBufferSceneIlluminationKey affect tone mapping. Is there any documentation I can refer to?
mengkeer
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