#include <SkGainmapInfo.h>

Public Types
enum class	BaseImageType { kSDR , kHDR }

enum class	Type { kDefault , kApple }

Public Member Functions
bool	isUltraHDRv1Compatible () const

sk_sp< SkData >	serialize () const

bool	operator== (const SkGainmapInfo &other) const

bool	operator!= (const SkGainmapInfo &other) const

Static Public Member Functions
static bool	ParseVersion (const SkData *data)

static bool	Parse (const SkData *data, SkGainmapInfo &info)

static sk_sp< SkData >	SerializeVersion ()

Public Attributes
SkColor4f	fGainmapRatioMin = {1.f, 1.f, 1.f, 1.0}

SkColor4f	fGainmapRatioMax = {2.f, 2.f, 2.f, 1.0}

SkColor4f	fGainmapGamma = {1.f, 1.f, 1.f, 1.f}

SkColor4f	fEpsilonSdr = {0.f, 0.f, 0.f, 1.0}

SkColor4f	fEpsilonHdr = {0.f, 0.f, 0.f, 1.0}

float	fDisplayRatioSdr = 1.f

float	fDisplayRatioHdr = 2.f

BaseImageType	fBaseImageType = BaseImageType::kSDR

Type	fType = Type::kDefault

sk_sp< SkColorSpace >	fGainmapMathColorSpace = nullptr

Detailed Description

Gainmap rendering parameters. Suppose our display has HDR to SDR ratio of H and we wish to display an image with gainmap on this display. Let B be the pixel value from the base image in a color space that has the primaries of the base image and a linear transfer function. Let G be the pixel value from the gainmap. Let D be the output pixel in the same color space as B. The value of D is computed as follows:

First, let W be a weight parameter determing how much the gainmap will be applied. W = clamp((log(H) - log(fDisplayRatioSdr)) / (log(fDisplayRatioHdr) - log(fDisplayRatioSdr), 0, 1)

Next, let L be the gainmap value in log space. We compute this from the value G that was sampled from the texture as follows: L = mix(log(fGainmapRatioMin), log(fGainmapRatioMax), pow(G, fGainmapGamma))

Finally, apply the gainmap to compute D, the displayed pixel. If the base image is SDR then compute: D = (B + fEpsilonSdr) * exp(L * W) - fEpsilonHdr If the base image is HDR then compute: D = (B + fEpsilonHdr) * exp(L * (W - 1)) - fEpsilonSdr

In the above math, log() is a natural logarithm and exp() is natural exponentiation. Note, however, that the base used for the log() and exp() functions does not affect the results of the computation (it cancels out, as long as the same base is used throughout).

This product includes Gain Map technology under license by Adobe.

Definition at line 43 of file SkGainmapInfo.h.

Member Enumeration Documentation

◆ BaseImageType

enum class SkGainmapInfo::BaseImageType

strong

Whether the base image is the SDR image or the HDR image.

Enumerator
kSDR
kHDR

Definition at line 71 of file SkGainmapInfo.h.

◆ Type

enum class SkGainmapInfo::Type

strong

The type of the gainmap image. If the type is kApple, then the gainmap image was originally encoded according to the specification at [0], and can be converted to the kDefault type by applying the transformation described at [1]. [0] https://developer.apple.com/documentation/appkit/images_and_pdf/ applying_apple_hdr_effect_to_your_photos [1] https://docs.google.com/document/d/1iUpYAThVV_FuDdeiO3t0vnlfoA1ryq0WfGS9FuydwKc

Enumerator
kDefault
kApple

Definition at line 85 of file SkGainmapInfo.h.

                    {
        kDefault,
        kApple,
    };

Member Function Documentation

◆ isUltraHDRv1Compatible()

bool SkGainmapInfo::isUltraHDRv1Compatible ( ) const

Return true if this can be encoded as an UltraHDR v1 image.

Definition at line 208 of file SkGainmapInfo.cpp.

                                                 {
    // UltraHDR v1 supports having the base image be HDR in theory, but it is largely
    // untested.
    if (fBaseImageType == BaseImageType::kHDR) {
        return false;
    }
    // UltraHDR v1 doesn't support a non-base gainmap math color space.
    if (fGainmapMathColorSpace) {
        return false;
    }
    return true;
}

◆ operator!=()

bool SkGainmapInfo::operator!= ( const SkGainmapInfo & other ) const

inline

Definition at line 137 of file SkGainmapInfo.h.

137{ return !(*this == other); }

◆ operator==()

bool SkGainmapInfo::operator== ( const SkGainmapInfo & other ) const

inline

Definition at line 127 of file SkGainmapInfo.h.

                                                             {
        return fGainmapRatioMin == other.fGainmapRatioMin &&
               fGainmapRatioMax == other.fGainmapRatioMax && fGainmapGamma == other.fGainmapGamma &&
               fEpsilonSdr == other.fEpsilonSdr && fEpsilonHdr == other.fEpsilonHdr &&
               fDisplayRatioSdr == other.fDisplayRatioSdr &&
               fDisplayRatioHdr == other.fDisplayRatioHdr &&
               fBaseImageType == other.fBaseImageType && fType == other.fType &&
               SkColorSpace::Equals(fGainmapMathColorSpace.get(),
                                    other.fGainmapMathColorSpace.get());
    }

◆ Parse()

bool SkGainmapInfo::Parse	(	const SkData *	data,
		SkGainmapInfo &	info
	)

static

Definition at line 229 of file SkGainmapInfo.cpp.

                                                                 {
    if (!data) {
        return false;
    }
    auto s = SkMemoryStream::MakeDirect(data->data(), data->size());
    return read_iso_gainmap_info(s.get(), info);
}

◆ ParseVersion()

bool SkGainmapInfo::ParseVersion ( const SkData * data )

static

If |data| contains an ISO 21496-1 version that is supported, return true. Otherwise return false.

Definition at line 221 of file SkGainmapInfo.cpp.

                                                   {
    if (!data) {
        return false;
    }
    auto s = SkMemoryStream::MakeDirect(data->data(), data->size());
    return read_iso_gainmap_version(s.get());
}

◆ serialize()

sk_sp< SkData > SkGainmapInfo::serialize ( ) const

Serialize an ISO 21496-1 version 0 blob containing this' gainmap parameters.

Definition at line 246 of file SkGainmapInfo.cpp.

                                             {
    SkDynamicMemoryWStream s;
    // Version.
    SkWStreamWriteU16BE(&s, 0);  // Minimum reader version
    SkWStreamWriteU16BE(&s, 0);  // Writer version
 
    // Flags.
    bool all_single_channel = is_single_channel(fGainmapRatioMin) &&
                              is_single_channel(fGainmapRatioMax) &&
                              is_single_channel(fGainmapGamma) && is_single_channel(fEpsilonSdr) &&
                              is_single_channel(fEpsilonHdr);
    uint8_t flags = 0;
    if (!fGainmapMathColorSpace) {
        flags |= kUseBaseColourSpaceMask;
    }
    if (!all_single_channel) {
        flags |= kIsMultiChannelMask;
    }
    s.write8(flags);
 
    // Base and altr headroom.
    switch (fBaseImageType) {
        case SkGainmapInfo::BaseImageType::kSDR:
            write_positive_rational_be(s, std::log2(fDisplayRatioSdr));
            write_positive_rational_be(s, std::log2(fDisplayRatioHdr));
            break;
        case SkGainmapInfo::BaseImageType::kHDR:
            write_positive_rational_be(s, std::log2(fDisplayRatioHdr));
            write_positive_rational_be(s, std::log2(fDisplayRatioSdr));
            break;
    }
 
    // Per-channel information.
    for (int i = 0; i < (all_single_channel ? 1 : 3); ++i) {
        write_rational_be(s, std::log2(fGainmapRatioMin[i]));
        write_rational_be(s, std::log2(fGainmapRatioMax[i]));
        write_positive_rational_be(s, 1.f / fGainmapGamma[i]);
        switch (fBaseImageType) {
            case SkGainmapInfo::BaseImageType::kSDR:
                write_rational_be(s, fEpsilonSdr[i]);
                write_rational_be(s, fEpsilonHdr[i]);
                break;
            case SkGainmapInfo::BaseImageType::kHDR:
                write_rational_be(s, fEpsilonHdr[i]);
                write_rational_be(s, fEpsilonSdr[i]);
                break;
        }
    }
    return s.detachAsData();
}

◆ SerializeVersion()

sk_sp< SkData > SkGainmapInfo::SerializeVersion ( )

static

Serialize an ISO 21496-1 version 0 blob containing only the version structure.

Definition at line 237 of file SkGainmapInfo.cpp.

                                              {
    SkDynamicMemoryWStream s;
    SkWStreamWriteU16BE(&s, 0);  // Minimum reader version
    SkWStreamWriteU16BE(&s, 0);  // Writer version
    return s.detachAsData();
}

Member Data Documentation

◆ fBaseImageType

BaseImageType SkGainmapInfo::fBaseImageType = BaseImageType::kSDR

Definition at line 75 of file SkGainmapInfo.h.

◆ fDisplayRatioHdr

float SkGainmapInfo::fDisplayRatioHdr = 2.f

Definition at line 66 of file SkGainmapInfo.h.

◆ fDisplayRatioSdr

float SkGainmapInfo::fDisplayRatioSdr = 1.f

If the output display's HDR to SDR ratio is less or equal than fDisplayRatioSdr then the SDR rendition is displayed. If the output display's HDR to SDR ratio is greater or equal than fDisplayRatioHdr then the HDR rendition is displayed. If the output display's HDR to SDR ratio is between these values then an interpolation between the two is displayed using the math above.

Definition at line 65 of file SkGainmapInfo.h.

◆ fEpsilonHdr

SkColor4f SkGainmapInfo::fEpsilonHdr = {0.f, 0.f, 0.f, 1.0}

Definition at line 56 of file SkGainmapInfo.h.

◆ fEpsilonSdr

SkColor4f SkGainmapInfo::fEpsilonSdr = {0.f, 0.f, 0.f, 1.0}

Parameters sometimes used in gainmap computation to avoid numerical instability.

Definition at line 55 of file SkGainmapInfo.h.

◆ fGainmapGamma

SkColor4f SkGainmapInfo::fGainmapGamma = {1.f, 1.f, 1.f, 1.f}

Definition at line 50 of file SkGainmapInfo.h.

◆ fGainmapMathColorSpace

sk_sp<SkColorSpace> SkGainmapInfo::fGainmapMathColorSpace = nullptr

If specified, color space to apply the gainmap in, otherwise the base image's color space is used. Only the color primaries are used, the transfer function is irrelevant.

Definition at line 95 of file SkGainmapInfo.h.

◆ fGainmapRatioMax

SkColor4f SkGainmapInfo::fGainmapRatioMax = {2.f, 2.f, 2.f, 1.0}

Definition at line 49 of file SkGainmapInfo.h.

◆ fGainmapRatioMin

SkColor4f SkGainmapInfo::fGainmapRatioMin = {1.f, 1.f, 1.f, 1.0}

Parameters for converting the gainmap from its image encoding to log space. These are specified per color channel. The alpha value is unused.

Definition at line 48 of file SkGainmapInfo.h.

◆ fType

Type SkGainmapInfo::fType = Type::kDefault

Definition at line 89 of file SkGainmapInfo.h.

The documentation for this struct was generated from the following files:

third_party/skia/include/private/SkGainmapInfo.h
third_party/skia/src/codec/SkGainmapInfo.cpp

Public Types

Public Member Functions

Static Public Member Functions

Public Attributes

Detailed Description

Member Enumeration Documentation

◆ BaseImageType

◆ Type

Member Function Documentation

◆ isUltraHDRv1Compatible()

◆ operator!=()

◆ operator==()

◆ Parse()

◆ ParseVersion()

◆ serialize()

◆ SerializeVersion()

Member Data Documentation

◆ fBaseImageType

◆ fDisplayRatioHdr

◆ fDisplayRatioSdr

◆ fEpsilonHdr

◆ fEpsilonSdr

◆ fGainmapGamma

◆ fGainmapMathColorSpace

◆ fGainmapRatioMax

◆ fGainmapRatioMin

◆ fType