Image Filtering Advanced Image filtering with GDI and DX HW accelerations

An introduction : domain terms Bitmap (let’s assume Bitmap == GDI+ Bitmap) System memory portion containing Pixel as color’s byte DX Surface System or Video memory portion representing a bitmap Texture Mainly 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

Image Filtering Advanced The speed part 1 : unsafe protected 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

Image Filtering Advanced Library structure Image Filtering Advanced

The key for success : the filter base class design Create all the temporary Images before your filter chain goes with its work! [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); } while (p != null); foreach (Bitmap bm in tmp) { bm.Dispose(); Image Filtering Advanced

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

Image => plane => polygon The speed part 3 : Get HW! A little trick to achieve the real magic Let’s pretend : Remember you gain speed but you get also limitations! Image => plane => polygon Image Filtering Advanced

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

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

Image Filtering Advanced HSL Stupid Example float4 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

Image Filtering Advanced The Idea Create a DX device on a control Create a 3D plane Put the image you want to process on the plane as a texture Use the Pixel Shader Program to make the GPU works for you Use the Control Graphics class to save your processed image. Image Filtering Advanced

A simple but real FX example Image Filtering Advanced

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

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

Image Filtering Advanced Example of transform HRESULT 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); // 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 Class If 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

Image Filtering Advanced References Enhanced Filter Library and Frame Dispatcer http://dotnet.di.unipi.it Image Filtering Advanced