EFFICIENT IMAGE PROCESSING ON ANDROID

Nicolas Roard

EFFICIENT IMAGE PROCESSING

• Works well on all hardware

• Fast, ideally realtime interaction

• Handles complex and flexible processing

• Handles large images

• Minimize memory usage

WE WANT TO HAVE OUR CAKE AND EAT IT TOO

ANDROID KITKATPHOTO EDITOR

• Non-destructive edits

• Full-size images processing

• Combine effects freely

• Easy to use, yet powerful: grow with the user

NON-DESTRUCTIVE EDITS

• Effects are modifiable or reversible without quality loss

• Allow re-edits of processed images

RENDERSCRIPT (RS)

• Cool thingy that let you do fast image processing

TIMELINE3 VERSIONS, 10 MONTHS

4.2 - NOVEMBER 2012

• Color FX (9 looks)

• 11 Borders

• Geometry: Straighten, Rotate, Crop, Mirror

• Filters & Tools

• Autocolor, Exposure, Vignette, Contrast, Shadows, Vibrance, Sharpness (RS-based), Curves, Hue, Saturation, BW Filter

• Non-destructive edits (in the editor -- save create a copy)

• Exposed history

G+ EDITOR - MAY 2013

• RenderScript implementations of Snapseed filters

• Frames, Film, Drama, Retrolux

• Non-destructive

• Cloud-based (local processing only used for caching and UI interactions)

4.3 - JULY 2013

• Move to RenderScript

• New 16 image-based borders (ported from Snapseed, RS-based)

• Filters & Tools

• Highlights, Improved Vignette

• Local adjustment (ported from Snapseed, RS-based)

• New Tablet UI, refined UI, introduction of the state panel instead of the history panel

4.4 - SEPTEMBER 2013

• Filters & Tools

• Custom borders, Drawing tool, negative, posterize

• RS filters: Graduated filter, Vignette, per channel saturation, sharpness/structure

• Refined UI (animations, etc.)

• Pinch to zoom enabled (full-res zoom)

• Re-edits enabled

• Background save service, export, print support

DEMO

SOME ADDITIONAL INFOS

• Phone and Tablet UI

• Filters in C & RenderScript

• Works on Full Size images -- largest tried was a 278MP image on a Nexus 7 2nd gen. Limited by available RAM.

• Nearly all of the editor is in AOSP!

IMAGE PROCESSING

PIPELINE

OriginalImage

PIPELINE

OriginalImage Filter

PIPELINE

OriginalImage Filter Processed

Image

IMAGE PROCESSING

• In Java

• In native code (JNI calls to C/C++)

• In OpenGLES2

• RenderScript

JAVA

• Use getPixel()

• Use getPixels()

• Use copyPixelsToBuffer() [premultiplied]

• GC calls. GC calls everywhere.

NATIVE CODE

• Pass a Bitmap through JNI to C/C++

• Quite fast & pretty easy to work with (pointer to the bitmap -- and no GC!)

• JNI / Native can be fastidious

• Handling different CPU architectures can be an issue

• Optimizations can be complicated

• JNI management

OPENGL ES 2.0

• Fast -- can write interactive processing

• Hard to ensure the shaders will perform well on all devices

• Limited in size (max texture size...)

• Needs adhoc shaders, i.e. fixed pipelines.

• Expensive to retrieve processed image

RENDERSCRIPT

“RENDERSCRIPT IS A FRAMEWORK FOR RUNNING COMPUTATIONALLY INTENSIVE TASKS AT HIGH PERFORMANCE ON ANDROID. RENDERSCRIPT IS PRIMARILY ORIENTED FOR USE WITH

DATA-PARALLEL COMPUTATION, ALTHOUGH SERIAL COMPUTATIONALLY INTENSIVE WORKLOADS CAN BENEFIT AS WELL.”

• Write “kernels” in a C99-like language with vector extensions and useful intrinsics

• RenderScript executes them in parallel, on the GPU or CPU

• Java used to manage lifetime of objects/allocations and control of execution

• Portability

RENDERSCRIPT

• Fast -- through LLVM optimizations and Parallelization

• Supports CPU / GPU

• Compatibility Library

• Easy to offload to the background

• Pretty easy to write

RENDERSCRIPT

• Cannot allocate memory from kernels, need to do it from outside

• RenderScript can be called from Java or from Native

• Compatibility library!

HOW?

• Optimized Math library

• Optimizations on the device

• Easier to read & maintain (vector math library helps)

ALLOCATIONS

• Bound to Scripts

• Can be bound to SurfaceTexture (producer & consumer)

• Can share memory between Allocation and Bitmap

HOW TO USE IT

#pragma version(1)#pragma rs java_package_name(com.example.rsdemo)

uchar4 __attribute__((kernel)) color(uchar4 in) { return in;}

1. SCRIPT

RenderScript mRS = RenderScript.create(mContext);

ScriptC_filter filter = new ScriptC_filter(mRS,mResources, R.raw.filter);

2. CREATE CONTEXT

Bitmap bitmapIn = BitmapFactory.decodeResource(getResources(), R.drawable.monumentvalley);

Bitmap bitmapOut = bitmapIn.copy(bitmapIn.getConfig(), true);

3. LOAD BITMAP

Allocation in = Allocation.createFromBitmap(mRS, bitmapIn, Allocation.MipmapControl.MIPMAP_NONE, Allocation.USAGE_SCRIPT

| Allocation.USAGE_SHARED);

Allocation out = Allocation.createTyped(mRS, in.getType());

4. CREATE ALLOCATIONS

filter.forEach_color(in, out); out.copyTo(bitmapOut);

5. APPLY THE SCRIPT

ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(mRS, Element.U8_4(mRS));

blur.setRadius(25.f);blur.setInput(in);blur.forEach(in);

SCRIPT INTRINSICS

READY TO USE• ScriptIntrinsic3DLUT

• ScriptIntrinsicBlend

• ScriptIntrinsicBlur

• ScriptIntrinsicColorMatrix

• ScriptIntrinsicConvolve3x3

• ScriptIntrinsicConvolve5x5

• ScriptIntrinsicLUT

• ScriptIntrinsicYuvToRGB

• ScriptGroup

PAINT IT BLACK (OR GRAY)

uchar4 __attribute__((kernel)) color(uchar4 in) { return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey(uchar4 in) { in.g = in.r; in.b = in.r; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey(uchar4 in) { in.gb = in.r; return in;}

SCRIPT

void Java_com_example_rsdemo_ProcessImage_processBitmap(JNIEnv* env, jobject this, jobject bitmap, jint width, jint height) {

unsigned char* rgb = 0; AndroidBitmap_lockPixels(env, bitmap, (void**) &rgb); int len = width * height * 4; int i; for (i = 0; i < len; i+=4) { int red = rgb[i]; rgb[i+1] = red; rgb[i+2] = red; } AndroidBitmap_unlockPixels(env, bitmap);}

NDK

LOCAL EFFECT

uchar4 __attribute__((kernel)) grey(uchar4 in) { in.g = in.r; in.b = in.r; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey1(uchar4 in, uint32_t x, uint32_t y) {

in.g = in.r; in.b = in.r; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey1(uchar4 in, uint32_t x, uint32_t y) {

float range = (float) x / width; uint32_t grey = (1 - range) * in.r; in.r = grey; in.g = grey; in.b = grey; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey1(uchar4 in, uint32_t x, uint32_t y) {

float range = (float) x / width; uint32_t grey = (1 - range) * in.r; in.r = grey; in.g = grey; in.b = grey; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey2(uchar4 in, uint32_t x, uint32_t y) {

float range = (float) x / width; uint32_t grey = (1 - range) * in.r; in.r = (in.r * range) + grey; in.g = (in.g * range) + grey; in.b = (in.b * range) + grey; return in;}

SCRIPT

uchar4 __attribute__((kernel)) grey3(uchar4 in, uint32_t x, uint32_t y) {

float range = (float) x / width; float4 pixel = rsUnpackColor8888(in); float grey = (1 - range) * pixel.r; pixel.r = pixel.r * range + grey; pixel.g = pixel.g * range + grey; pixel.b = pixel.b * range + grey; return rsPackColorTo8888(

clamp(pixel, 0.f, 1.0f));}

SCRIPT

uchar4 __attribute__((kernel)) grey4(uchar4 in, uint32_t x, uint32_t y) {

float range = (float) x / width; float4 pixel = rsUnpackColor8888(in); float grey = (1 - range) * pixel.r; pixel.rgb = pixel.rgb * range + grey; return rsPackColorTo8888(

clamp(pixel, 0.f, 1.0f));}

SCRIPT

EXAMPLE: BLOOM

• Select the bright pixels

• Blur the result

• Add the blurred bright pixels back to the image

private void brightPass(int[] pixels, int width, int height) { int threshold = (int) (brightnessThreshold * 255); int r; int g; int b;

int luminance; int[] luminanceData = new int[3 * 256]; // pre-computations for conversion from RGB to YCC for (int i = 0; i < luminanceData.length; i += 3) { luminanceData[i ] = (int) (i * 0.2125f); luminanceData[i + 1] = (int) (i * 0.7154f); luminanceData[i + 2] = (int) (i * 0.0721f); }

WITH JAVA

int index = 0; for (int y = 0; y < height; y++) { for (int x = 0; x < width; x++) { int pixel = pixels[index];

// unpack the pixel's components r = pixel >> 16 & 0xFF; g = pixel >> 8 & 0xFF; b = pixel & 0xFF; // compute the luminance luminance = luminanceData[r * 3] + luminanceData[g * 3 + 1] + luminanceData[b * 3 + 2]; // apply the treshold to select the brightest pixels luminance = Math.max(0, luminance - threshold); int sign = (int) Math.signum(luminance);

// pack the components in a single pixel pixels[index] = 0xFF000000 | (r * sign) < < 16 | (g * sign) << 8 | (b * sign);

index++; } }}

uniform sampler2D baseImage;uniform float brightPassThreshold;

void main(void) { vec3 luminanceVector = vec3(0.2125, 0.7154, 0.0721); vec4 sample = texture2D(baseImage, gl_TexCoord[0].st);

float luminance = dot(luminanceVector, sample.rgb); luminance = max(0.0, luminance - brightPassThreshold); sample.rgb *= sign(luminance); sample.a = 1.0;

gl_FragColor = sample;}

WITH GL SHADER

float brightPassThreshold;

uchar4 __attribute__((kernel)) brightPass(uchar4 in) { float3 luminanceVector = { 0.2125, 0.7154, 0.0721 }; float4 pixel = rsUnpackColor8888(in); float luminance = dot(luminanceVector, pixel.rgb);

luminance = max(0.0f, luminance - brightPassThreshold); pixel.rgb *= sign(luminance); pixel.a = 1.0; return rsPackColorTo8888(clamp(pixel, 0.f, 1.0f));}

WITH RENDERSCRIPT

ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(mRS, Element.U8_4(mRS));ScriptIntrinsicBlend blend = ScriptIntrinsicBlend.create(mRS, Element.U8_4(mRS));

filter.set_brightPassThreshold(0.15f);filter.forEach_brightPass(in, out); blur.setRadius(25.f);blur.setInput(out);blur.forEach(out);blend.forEachAdd(in, out);

out.copyTo(bitmapOut);

JAVA-SIDE

WORKING WELL EVERYWHERE

WORKING WELL ON ALL HARDWARE

• Architect for the worst

• Scale with the device capabilities

• Screen size / dpi

• Available memory

• Available CPU / GPU

• Think about what is a downgraded experience

LOADING• Load in the background

• AsyncTask, or use a background thread

• Bitmaps loading

• query the size

• inSampleSize

• reuseBitmap

• BitmapRegionDecoder

QUERY THE SIZE

BitmapFactory.Options options =new BitmapFactory.Options();

options.inJustDecodeBounds = true;BitmapFactory.decodeResource(

getResources(), R.id.myimage, options);int imageHeight = options.outHeight;int imageWidth = options.outWidth;String imageType = options.outMimeType;

INSAMPLESIZE

• Only load what you need

• needs to be a power of two, so for a 2048x2048 image,

• insamplesize=2 => 1024x1024 image

• insamplesize=4 => 512x512 image

CALCULATE INSAMPLESIZE

if (bounds.width() > destination.width()) {int sampleSize = 1;int w = bounds.width();while (w > destination.width()) {

sampleSize *= 2;w /= sampleSize;

}options.inSampleSize = sampleSize;

}

REUSE BITMAP

BitmapFactory.Options options;(...)Bitmap inBitmap = ...(...)options.inBitmap = inBitmap;

API level 11 (Android 3.0)Before API level 19 (Android 4.4) only same size

BITMAP REGIONDECODER

InputStream is = ...BitmapRegionDecoder decoder =

BitmapRegionDecoder.newInstance(is, false);Rect imageBounds = ...Bitmap bitmap =

decoder.decodeRegion(imageBounds, options);

API level 11 (Android 3.0)

PIPELINE

PIPELINE

• Run in a background service (used when saving too)

• Mix C, RenderScript, java filtering (canvas draw)

• multiple pipelines in parallel (direct preview, highres, icons, full res, geometry, saving)

FLEXIBLE PROCESSING

• Unbounded pipeline

• No fixed order

• Complex filters

• Geometry-based

• Global

• Local

FILTER TYPES

Color Fx Geometry * Borders

Crop

Straighten

Rotate

Mirror

Contrast

Saturation

Local

Vignette

Image-based

Parametric

Color transforms

COLOR FX - 3D LUTVintage

Instant

Washout

X-Process

CACHING

• Cache RS scripts, allocations

• Cache original bitmaps

• Aggressively destroy/recycle resources in filters to keep memory low

• If possible, filters should process the input bitmap directly

• N-1 cache

MEMORY USAGE

• Bitmap cache heavily reusing bitmaps

• LruCache class (available in support lib too)

• Pick image sizes depending on the device resolution / DPI

• Have a path ready for a downgraded experience

DEVICE CAPABILITIES

• Ask the system

• Runtime.getRuntime().maxMemory()

• New isLowRamDevice() API

• Handles low-memory signals

• Handles java.lang.OutOfMemory exceptions

PIPELINE CACHE

OriginalImage

PIPELINE CACHE

OriginalImage Filter Processed

Image

REALISTICALLY...

OriginalImage

REALISTICALLY...

OriginalImage Filter Processed

ImageFilter Filter Filter

PROCESSING

OriginalImage Filter Processed

ImageFilter Filter Filter

PROCESSING

OriginalImage Filter Processed

ImageFilter Filter Filter

PROCESSING

OriginalImage Filter Processed

ImageFilter Filter Filter

N-1 CACHING

OriginalImage Filter Processed

ImageFilter Filter FilterFilter

N-1 CACHING

OriginalImage Filter Processed

ImageFilter Filter FilterFilter

N-1 CACHING

OriginalImage Filter Processed

ImageFilter Filter FilterFilter

N-1 CACHING

OriginalImage Filter Processed

ImageFilter Filter FilterFilter

N-1 CACHING

OriginalImage Filter Processed

ImageFilter Filter Filter

N-1 CACHING

• No silver bullet

• Only really useful when the user manipulates the last filters of the pipeline...

• ...but this is after all the more common scenario!

REALTIME INTERACTION

REALTIME INTERACTION

• Background processing

• Minimize allocations -- Careful with Garbage Collection!

• Optimized filters, RenderScript helps

• Caching in the pipeline

• Low/High resolution preview

PREVIEW SYSTEM

Bitmap

Preset

Bitmap

Preset

Bitmap

Preset

UI Thread Processing Thread

PREVIEW SYSTEM

Bitmap

Preset

Bitmap

Preset

Bitmap

Preset

UI Thread Processing Thread

PREVIEW

Continuous preview

High-res preview

Full resolution

PREVIEW SYSTEM

Low-res preview

High-res preview

Full-res preview

If new request, delay more

Request

HOW TO CHEAT

• The triple-buffer preview can have a low resolution

• The UI elements and controls are animated and manipulated at 60 fps on the UI thread

• The rendering pipeline can (and needs to) be interrupted

INTERRUPTION IN RENDERSCRIPT

LaunchOptions options = new LaunchOptions();options.setX(xStart, xEnd);options.setY(yStart, yEnd);mScript.forEach_vignette(in, out, options);

LaunchOptions options = new LaunchOptions(); boolean even = true; int tile = 128; int height = bitmapIn.getHeight(); int width = bitmapIn.getWidth(); for (int yStart = 0; yStart < height; yStart += tile) { for (int xStart = 0; xStart < width; xStart += tile) { int xEnd = xStart + tile; int yEnd = yStart + tile; options.setX(xStart, xEnd); options.setY(yStart, yEnd); if (even) { filter.forEach_grey(in, out, options); } else { filter.forEach_color(in, out, options); } even = !even; } }

FULL RESOLUTION PREVIEW

FULL RESOLUTIONPREVIEW

• Ideally, we should use a tile-based rendering

• At the moment, we use BitmapFactory region decoder instead

• Filters need to be able to handle partial regions

• future payoff: streaming save

FUTURE

FUTURE -- IN THE PHOTO EDITOR

• Merging filters

• RenderScript

• At the pipeline level (color cubes...)

• Streaming saving

• Some code is there (AOSP), but not used

FUTURE -- IN ANDROID FRAMEWORK

• TileView

• Adding filtering pipeline in android framework

• Image loader improvements

• RAW support? Color correction?

13223x559870MP image

~60 tiles, ~15Mb

13223x559870MP image

~60 tiles, ~15Mb

TILEVIEW

TileView TileViewAdapter

ImageTileViewAdapterTileGrid

TileCache TestTileViewAdapterTile

TILEVIEW ADAPTER

public interface TileViewAdapter { public int getTileSize(); public int getContentWidth(); public int getContentHeight(); public void onPaint(float scale,

float dx, float dy, Bitmap bitmap); public Bitmap getFullImage(int max); void setDebug(boolean debug);}

QUESTIONS, SUGGESTIONS?

• RenderScript documentation:

• http://developer.android.com/guide/topics/renderscript/compute.html

• contact: nicolasroard@google.com