Added in API level 34

Summary: Inherited Constants | Fields | Ctors | Methods | Inherited Methods

Gainmap

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Kotlin |Java

public final class Gainmap
extends Object implements Parcelable

java.lang.Object
↳	android.graphics.Gainmap

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Gainmap represents a mechanism for augmenting an SDR image to produce an HDR one with variable display adjustment capability. It is a combination of a set of metadata describing how to apply the gainmap, as well as either a 1 (such as Bitmap.Config.ALPHA_8 or 3 (such as Bitmap.Config.ARGB_8888 with the alpha channel ignored) channel Bitmap that represents the gainmap data itself.

When rendering to an ActivityInfo.COLOR_MODE_HDR activity, the hardware accelerated Canvas will automatically apply the gainmap when sufficient HDR headroom is available.

Gainmap Structure

The logical whole of a gainmap'd image consists of a base Bitmap that represents the original image as would be displayed without gainmap support in addition to a gainmap with a second enhancement image. In the case of a JPEG, the base image would be the typical 8-bit SDR image that the format is commonly associated with. The gainmap image is embedded alongside the base image, often at a lower resolution (such as 1/4th), along with some metadata to describe how to apply the gainmap. The gainmap image itself is then a greyscale image representing the transformation to apply onto the base image to reconstruct an HDR rendition of it.

As such these "gainmap images" consist of 3 parts - a base Bitmap with a Bitmap.getGainmap() that returns an instance of this class which in turn contains the enhancement layer represented as another Bitmap, accessible via getGainmapContents()

Applying a gainmap manually

When doing custom rendering such as to an OpenGL ES or Vulkan context, the gainmap is not automatically applied. In such situations, the following steps are appropriate to render the gainmap in combination with the base image.

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 determining how much the gainmap will be applied.

   W = clamp((log(H)                      - log(minDisplayRatioForHdrTransition)) /
             (log(displayRatioForFullHdr) - log(minDisplayRatioForHdrTransition), 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(ratioMin), log(ratioMax), pow(G, gamma))

Finally, apply the gainmap to compute D, the displayed pixel. If the base image is SDR then compute:

   D = (B + epsilonSdr) * exp(L * W) - epsilonHdr

In the above math, log() is a natural logarithm and exp() is natural exponentiation. The base for these functions cancels out and does not affect the result, so other bases may be used if preferred.

Summary

Inherited constants

From interface android.os.Parcelable int CONTENTS_FILE_DESCRIPTOR Descriptor bit used with describeContents(): indicates that the Parcelable object's flattened representation includes a file descriptor. int PARCELABLE_WRITE_RETURN_VALUE Flag for use with writeToParcel(Parcel, int): the object being written is a return value, that is the result of a function such as "Parcelable someFunction()", "void someFunction(out Parcelable)", or "void someFunction(inout Parcelable)".

Fields
public static final Creator<Gainmap>	CREATOR

Public constructors
Gainmap(Bitmap gainmapContents) Creates a gainmap from a given Bitmap.
Gainmap(Gainmap gainmap, Bitmap gainmapContents) Creates a new gainmap using the provided gainmap as the metadata source and the provided bitmap as the replacement for the gainmapContents

Public methods
int	describeContents() No special parcel contents.
float	getDisplayRatioForFullHdr() Gets the hdr/sdr ratio at which point applying the gainmap results in an HDR rendition
float[]	getEpsilonHdr() Gets the hdr epsilon.
float[]	getEpsilonSdr() Gets the sdr epsilon.
Bitmap	getGainmapContents()
float[]	getGamma() Gets the gainmap gamma.
float	getMinDisplayRatioForHdrTransition() Gets the hdr/sdr ratio below which applying the gainmap results in an SDR rendition.
float[]	getRatioMax() Gets the gainmap ratio max.
float[]	getRatioMin() Gets the gainmap ratio max.
void	setDisplayRatioForFullHdr(float max) Sets the hdr/sdr ratio at which point applying the gainmap results in an HDR rendition.
void	setEpsilonHdr(float r, float g, float b) Sets the hdr epsilon which is used to avoid numerical instability.
void	setEpsilonSdr(float r, float g, float b) Sets the sdr epsilon which is used to avoid numerical instability.
void	setGainmapContents(Bitmap bitmap) Sets the image data of the gainmap.
void	setGamma(float r, float g, float b) Sets the gainmap gamma.
void	setMinDisplayRatioForHdrTransition(float min) Sets the hdr/sdr ratio below which applying the gainmap results in an SDR rendition.
void	setRatioMax(float r, float g, float b) Sets the gainmap ratio max.
void	setRatioMin(float r, float g, float b) Sets the gainmap ratio min.
void	writeToParcel(Parcel dest, int flags) Write the gainmap to the parcel.

Inherited methods
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
From interface android.os.Parcelable abstract int describeContents() Describe the kinds of special objects contained in this Parcelable instance's marshaled representation. abstract void writeToParcel(Parcel dest, int flags) Flatten this object in to a Parcel.

Fields

CREATOR

Added in API level 34

public static final Creator<Gainmap> CREATOR

Public constructors

Gainmap

Added in API level 34

public Gainmap (Bitmap gainmapContents)

Creates a gainmap from a given Bitmap. The caller is responsible for setting the various fields to the desired values. The defaults are as follows:

• Ratio min is 1f, 1f, 1f
• Ratio max is 2f, 2f, 2f
• Gamma is 1f, 1f, 1f
• Epsilon SDR is 0f, 0f, 0f
• Epsilon HDR is 0f, 0f, 0f
• Display ratio SDR is 1f
• Display ratio HDR is 2f

It is strongly recommended that at least the ratio max and display ratio HDR are adjusted to better suit the given gainmap contents.

Parameters
gainmapContents	Bitmap: This value cannot be null.

Gainmap

Added in API level 35

public Gainmap (Gainmap gainmap, 
                Bitmap gainmapContents)

Creates a new gainmap using the provided gainmap as the metadata source and the provided bitmap as the replacement for the gainmapContents

Parameters
gainmap	Gainmap: This value cannot be null.
gainmapContents	Bitmap: This value cannot be null.

Public methods

describeContents

Added in API level 34

public int describeContents ()

No special parcel contents.

Returns
int	a bitmask indicating the set of special object types marshaled by this Parcelable object instance. Value is either 0 or CONTENTS_FILE_DESCRIPTOR

getDisplayRatioForFullHdr

Added in API level 34

public float getDisplayRatioForFullHdr ()

Gets the hdr/sdr ratio at which point applying the gainmap results in an HDR rendition

Returns
float	This value cannot be null.

getEpsilonHdr

Added in API level 34

public float[] getEpsilonHdr ()

Gets the hdr epsilon. For single-plane gainmaps, all 3 components should be the same. The components are in r, g, b order.

Returns
float[]	This value cannot be null.

getEpsilonSdr

Added in API level 34

public float[] getEpsilonSdr ()

Gets the sdr epsilon. For single-plane gainmaps, all 3 components should be the same. The components are in r, g, b order.

Returns
float[]	This value cannot be null.

getGainmapContents

Added in API level 34

public Bitmap getGainmapContents ()

Returns
Bitmap	Returns the image data of the gainmap represented as a Bitmap. This is represented as a Bitmap for broad API compatibility, however certain aspects of the Bitmap are ignored such as Bitmap.getColorSpace() or Bitmap.getGainmap() as they are not relevant to the gainmap's enhancement layer. This value cannot be null.

getGamma

Added in API level 34

public float[] getGamma ()

Gets the gainmap gamma. For single-plane gainmaps, all 3 components should be the same. The components are in r, g, b order.

Returns
float[]	This value cannot be null.

getMinDisplayRatioForHdrTransition

Added in API level 34

public float getMinDisplayRatioForHdrTransition ()

Gets the hdr/sdr ratio below which applying the gainmap results in an SDR rendition.

Returns
float	This value cannot be null.

getRatioMax

Added in API level 34

public float[] getRatioMax ()

Gets the gainmap ratio max. For single-plane gainmaps, all 3 components should be the same. The components are in r, g, b order.

Returns
float[]	This value cannot be null.

getRatioMin

Added in API level 34

public float[] getRatioMin ()

Gets the gainmap ratio max. For single-plane gainmaps, all 3 components should be the same. The components are in r, g, b order.

Returns
float[]	This value cannot be null.

setDisplayRatioForFullHdr

Added in API level 34

public void setDisplayRatioForFullHdr (float max)

Sets the hdr/sdr ratio at which point applying the gainmap results in an HDR rendition.

Parameters
max	float: The hdr/sdr ratio at which point applying the gainmap results in an HDR rendition. Must be >= 1.0f Value is 1.0f or greater

setEpsilonHdr

Added in API level 34

public void setEpsilonHdr (float r, 
                float g, 
                float b)

Sets the hdr epsilon which is used to avoid numerical instability. For single-plane gainmaps, r, g, and b should be the same.

Parameters
r	float
g	float
b	float

setEpsilonSdr

Added in API level 34

public void setEpsilonSdr (float r, 
                float g, 
                float b)

Sets the sdr epsilon which is used to avoid numerical instability. For single-plane gainmaps, r, g, and b should be the same.

Parameters
r	float
g	float
b	float

setGainmapContents

Added in API level 34

public void setGainmapContents (Bitmap bitmap)

Sets the image data of the gainmap. This is the 1 or 3 channel enhancement layer to apply to the base image. This is represented as a Bitmap for broad API compatibility, however certain aspects of the Bitmap are ignored such as Bitmap.getColorSpace() or Bitmap.getGainmap() as they are not relevant to the gainmap's enhancement layer.

Parameters
bitmap	Bitmap: The non-null bitmap to set as the gainmap's contents

setGamma

Added in API level 34

public void setGamma (float r, 
                float g, 
                float b)

Sets the gainmap gamma. For single-plane gainmaps, r, g, and b should be the same.

Parameters
r	float
g	float
b	float

setMinDisplayRatioForHdrTransition

Added in API level 34

public void setMinDisplayRatioForHdrTransition (float min)

Sets the hdr/sdr ratio below which applying the gainmap results in an SDR rendition.

Parameters
min	float: The minimum hdr/sdr ratio at which point applying the gainmap results in an SDR rendition. Must be >= 1.0f Value is 1.0f or greater

setRatioMax

Added in API level 34

public void setRatioMax (float r, 
                float g, 
                float b)

Sets the gainmap ratio max. For single-plane gainmaps, r, g, and b should be the same.

Parameters
r	float
g	float
b	float

setRatioMin

Added in API level 34

public void setRatioMin (float r, 
                float g, 
                float b)

Sets the gainmap ratio min. For single-plane gainmaps, r, g, and b should be the same.

Parameters
r	float
g	float
b	float

writeToParcel

Added in API level 34

public void writeToParcel (Parcel dest, 
                int flags)

Write the gainmap to the parcel.

Parameters
dest	Parcel: Parcel object to write the gainmap data into This value cannot be null.
flags	int: Additional flags about how the object should be written.