Fuzzy Top Edge with GDIPlus Resize

Question

I'm using the following code to resize a bitmap using GDI+ in C. I'm getting gray values for the top edge even for images where that area should be white. The problem disappears when the interpolation is nearest neighbor. However, I tried bicubic interpolation with ImageMagick and it seems fine. Any limitations problems I should know of? Is my method of scaling wrong somehow? Thanks!

(inputs: destSize : destination Gdiplus::Size m_pBitmap : source bitmap)

Rect destRect(Point(0,0), destSize);
Bitmap *pBitmap24BPP =  new Bitmap(destSize.Width, destSize.Height, PixelFormat24bppRGB);
pBitmap24BPP->SetResolution(m_pBitmap->GetHorizontalResolution(), m_pBitmap->GetVerticalResolution());  
Graphics *pGraphics = Graphics::FromImage(pBitmap24BPP);
pGraphics->SetInterpolationMode(InterpolationModeHighQualityBilinear);
pGraphics->DrawImage(m_pBitmap, destRect, 0, 0, m_pBitmap->GetWidth(), m_pBitmap->GetHeight()   , UnitPixel, NULL);

//cleanup

Answer 1

i've been seeing similar things. i've not had time to research it, but i have a feeling it is because the GDI+ image resizer is mistakenly using pixels values "off the top edge", which would be all zero - making it black.

Proper image resizing should recognize that you've reached the edge of the image, and handle it appropriately.