C# GDI+ Image Resize Function

Question

So my logic is flawed and I need a better and correct way to resize an image in my c# app

I need a function similar to this setup

public void ResizeI         


        

Answer 1

I would certainly not use GetThumbnailImage as it would be shocking - for good resolution without resorting to DX or OpenL etc, I'd use something like the following (from my own graphics library I use in many windows apps - I have shared this a few times before so there may be variants float around the net). There are 3 methods here - the GetNonIndexedPixelFormat method is used to stop GDI crashing when passed pixel formats it can't handle (comments explain it). The first allows scaling by a factor (Zoom) and the last allows fixed size rescaling whilst keeping the aspect ratio (but can easily be modified if you want to skew it instead). Enjoy:

    /// 

    /// Scale Image By A Percentage - Scale Factor between 0 and 1.
    /// 
    /// Image: Image to scale
    /// Float: Sclae Value - 0 to 1 are the usual values
    /// Image: Scaled Image
    public static Image ScaleByPercent(Image originalImg, float ZoomFactor)
    {    
        int destWidth = (int)((float)originalImg.Width * ZoomFactor);
        int destHeight = (int)((float)originalImg.Height * ZoomFactor);

        Bitmap bmPhoto = new Bitmap(destWidth, destHeight, GetNonIndexedPixelFormat(originalImg)); // PixelFormat.Format24bppRgb);

        bmPhoto.SetResolution(originalImg.HorizontalResolution,  originalImg.VerticalResolution);

        Graphics grPhoto = Graphics.FromImage(bmPhoto);
        grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic;

        grPhoto.DrawImage(originalImg,
            new Rectangle(0, 0, destWidth, destHeight),
            new Rectangle(0, 0, originalImg.Width, originalImg.Height),
            GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }

    /// 

    /// Gets the closest non-indexed pixel format
    /// 
    /// Image: Original image
    /// PixelFormat: Closest non-pixel image format
    public static PixelFormat GetNonIndexedPixelFormat(Image originalImage)
    {
        /*
         * These formats cause an error when creating a GDI Graphics Oblect, so must be converted to non Indexed
         * Error is "A graphics object cannot be created from an image that has an indexed pixel format"
         * 
            PixelFormat.Undefined 
            PixelFormat.DontCare 
            PixelFormat.1bppIndexed
            PixelFormat.4bppIndexed
            PixelFormat.8bppIndexed
            PixelFormat.16bppGrayScale
            PixelFormat.16bppARGB1555
         * 
         * An attempt is made to use the closest (i.e. smallest fitting) format that will hold the palette.
         */

        switch (originalImage.PixelFormat)
        {
            case PixelFormat.Undefined: 
                //This is also the same Enumation as PixelFormat.DontCare:
                return PixelFormat.Format24bppRgb;
            case PixelFormat.Format1bppIndexed:
                return PixelFormat.Format16bppRgb555;
            case PixelFormat.Format4bppIndexed:
                return PixelFormat.Format16bppRgb555;
            case PixelFormat.Format8bppIndexed:
                return PixelFormat.Format16bppRgb555;
            case PixelFormat.Format16bppGrayScale:
                return PixelFormat.Format16bppArgb1555;
            case PixelFormat.Format32bppArgb:
                return PixelFormat.Format24bppRgb;                
            default:
                return originalImage.PixelFormat;
        }
    }

    /// 

    /// Resize image keeping aspect ratio.
    /// 
    /// Image: Image to scale
    /// Int: Required width in pixels
    /// Int: Required height in pixels
    /// Color: Background colour
    /// Image: Scaled Image
    public static Image Resize(Image originalImg, int Width, int Height, Color BackgroundColour)
    {
        int destX = 0;
        int destY = 0;

        float nPercent = 0f;

        float nPercentW = ((float)Width / (float)originalImg.Width);
        float nPercentH = ((float)Height / (float)originalImg.Height);

        if (nPercentH < nPercentW)
        {
            nPercent = nPercentH;
            destX = System.Convert.ToInt16(((float)Width - ((float)originalImg.Width * nPercent)) / 2f);
        }
        else
        {
            nPercent = nPercentW;
            destY = System.Convert.ToInt16(((float)Height - ((float)originalImg.Height * nPercent)) / 2f);
        }

        int destWidth = (int)(originalImg.Width * nPercent);
        int destHeight = (int)(originalImg.Height * nPercent);

        Bitmap bmPhoto = new Bitmap(Width, Height, GetNonIndexedPixelFormat(originalImg)); // PixelFormat.Format24bppRgb);

        bmPhoto.SetResolution(originalImg.HorizontalResolution, originalImg.VerticalResolution);

        Graphics grPhoto = Graphics.FromImage(bmPhoto);
        grPhoto.Clear(BackgroundColour);
        grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic;

        grPhoto.DrawImage(originalImg,
            new Rectangle(destX, destY, destWidth, destHeight),
            new Rectangle(0, 0, originalImg.Width, originalImg.Height), GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }