Image Filtering Advanced

Image Filtering Advanced

Image filtering with GDI and DX HW accelerations

Image Filtering Advanced

An introduction : domain terms

♦ Bitmap (let’s assume Bitmap == GDI+ Bitmap)System memory portion containing Pixel as color’s byte

♦ DX SurfaceSystem or Video memory portion representing a bitmap

♦ TextureMainly Video memory portion containing a bitmap that

will be mapped onto a polygon

Image Filtering Advanced

Enhanced Image Filter Library

♦ What does a filter do?♦ What is a filter?♦ What is a filter chain?

A filter is a function from image to image,A filter chain is a functional composition so,

it’s a function again.

Image Filtering Advanced

The speed part 1 : unsafeprotected override void filter(Bitmap b, Bitmap[] temp) {

BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); int stride = bmData.Stride; System.IntPtr Scan0 = bmData.Scan0;

unsafe {byte * p = (byte *)(void *)Scan0;

int nOffset = stride - b.Width*3;int nWidth = b.Width * 3;

for(int y=0;y<b.Height;++y) { for(int x=0; x < nWidth; ++x ) {

p[0] = (byte)(255-p[0]);++p;

} p += nOffset;}

} b.UnlockBits(bmData);}

}

This way is faster than accessing pixels through the GetPixel GDI function

Image Filtering Advanced

Filter

Brightness

ColorCorrector

Contrast

Conv3x3

EdgeDetectConvolution EdgeDetectDifference

EdgeDetectHomogenity

EdgeDetectHorizontal

EdgeDetectQuick

EdgeDetectVertical

EdgeEnhance EmbossLaplacian

Gamma

GaussianBlur

GrayScale

Invert

MeanRemoval

Sharpen

Smooth

Library structure

Image Filtering Advanced

The key for success : the filter base class design

[Serializable] public abstract class Filter {

private Filter next;protected Filter(Filter f) { next = f;}protected Filter() { next = null;}protected abstract void filter(Bitmap b, Bitmap[] temp);

protected abstract int NumCopies { get; }

public BaseConf GetConfig(){ return new BaseConf();}

public void Apply(Bitmap b) { int n = this.NumCopies; Filter p = next; while (p != null) {

n = Math.Max(n, p.NumCopies);p = p.next;

} Bitmap[] tmp = new Bitmap[n]; for (int i = 0; i < n; i++)

tmp[i] = new Bitmap(b.Width, b.Height); p = this; do {

p.filter(b, tmp);p = p.next;

} while (p != null); foreach (Bitmap bm in tmp) {

bm.Dispose(); }}

}

Create all the temporaryImages before your filterchain goes with its work!

Image Filtering Advanced

The speed part 2 : ngen♦ Let’s get native!Run the ngen tool on the filter library

assembly to get it compiled once for all.

Image Filtering Advanced

♦ A little trick to achieve the real magic♦ Let’s pretend :

♦ Remember you gain speed but you get also limitations!

Image => plane => polygon

The speed part 3 : Get HW!

Image Filtering Advanced

DX Structure♦ We can use the HW

3D acceleration to boost 2D image filtering using the Programmable Pixel Shader

Image Filtering Advanced

HSL with DX 9♦ Cross Hardware language!♦ Can contains multiple techniques and

passes!♦ Exposes a large number of common

function as lerp and so on

Image Filtering Advanced

HSL Stupid Examplefloat4 Light(float3 LightDir : TEXCOORD1, uniform

float4 LightColor, float2 texcrd : TEXCOORD0, uniform sampler samp) : COLOR

{ float3 Normal = tex2D(samp,texcrd); return dot((Normal*2 - 1), LightDir)*LightColor;

}

Image Filtering Advanced

The Idea1. Create a DX device on a control2. Create a 3D plane3. Put the image you want to process on

the plane as a texture4. Use the Pixel Shader Program to make

the GPU works for you5. Use the Control Graphics class to save

your processed image.

Image Filtering Advanced

A simple but real FX example

Image Filtering Advanced

And the cons?Here we are . . .♦ You can use only power of 2 sized bitmap♦ The display size is the maximum size for

the output image. . . But you get a common PC running as it’s

got a real expensive (and dedicated) DSP!

Image Filtering Advanced

The Direct Show way♦ DShow use a graph from sources to

renderes (audio and video)♦ Along the graph you can have filters♦ 2 approaches

– In place transformations– Not in place transformations

♦ Only C++ (the unmanaged one!)

Image Filtering Advanced

CTransformFilter::Transform

♦ This filter uses the CTransformInputPin class for its input pin, and the CTransformOutputPin class for its output pin.

♦ Use this base class if you want to try filter and then pass it through the graph

♦ Beware of memory leak!

Image Filtering Advanced

Example of transformHRESULT CRleFilter::Transform(IMediaSample *pSource, IMediaSample *pDest) {

// Get pointers to the underlying buffers. BYTE *pBufferIn, *pBufferOut; hr = pSource->GetPointer(&pBufferIn); if (FAILED(hr)) {

return hr; } hr = pDest->GetPointer(&pBufferOut); if (FAILED(hr)) {

return hr; } // Process the data. DWORD cbDest = EncodeFrame(pBufferIn, pBufferOut); KASSERT((long)cbDest <= pDest->GetSize()); pDest->SetActualDataLength(cbDest); pDest->SetSyncPoint(TRUE); return S_OK;

}

Image Filtering Advanced

CTransInPlaceFilter::Transform

♦ Transform the input sample in place♦ Use it for real real-time processing♦ What do you want more?

Image Filtering Advanced

The Frame Dispatcer ClassIf you want to apply filter to a real time

camera or to an avi file in C# there’s an utility from the Medialab (university of Pisa) that can help you to get your frames inside a managed application!

Image Filtering Advanced

References♦ Enhanced Filter Library and Frame

Dispatcer– http://dotnet.di.unipi.it