some issues with downsized images and their increased file sizes in c#

Question

Hi ,

I have a class which helps me out to re-size my images to a specified image size but the problem is with the file sizes of the output images—actually it's kinda funny but here is the thing:

the original image is : 800x600 24bit 96dpi file-size : 82kb

the re-size image is : 466x340 24bit 96dpi file-size : 366kb

what should I do? is there any 3rd party component or open source project according to this issue?

here is my mentioned class :

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;


public class imageClass
{
    public enum Dimensions
    {
        Width,
        Height
    }
    public enum AnchorPosition
    {
        Top,
        Center,
        Bottom,
        Left,
        Right
    }

    public static Image ScaleByPercent(Image imgPhoto, int Percent)
    {
        float nPercent = ((float)Percent / 100);

        int sourceWidth = imgPhoto.Width;
        int sourceHeight = imgPhoto.Height;
        int sourceX = 0;
        int sourceY = 0;

        int destX = 0;
        int destY = 0;
        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap bmPhoto = new Bitmap(destWidth, destHeight, PixelFormat.Format24bppRgb);
        bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

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

        grPhoto.DrawImage(imgPhoto,
            new Rectangle(destX, destY, destWidth, destHeight),
            new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight),
            GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }
    public static Image ConstrainProportions(Image imgPhoto, int Size, Dimensions Dimension)
    {
        int sourceWidth = imgPhoto.Width;
        int sourceHeight = imgPhoto.Height;
        int sourceX = 0;
        int sourceY = 0;
        int destX = 0;
        int destY = 0;
        float nPercent = 0;

        switch (Dimension)
        {
            case Dimensions.Width:
                nPercent = ((float)Size / (float)sourceWidth);
                break;
            default:
                nPercent = ((float)Size / (float)sourceHeight);
                break;
        }

        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap bmPhoto = new Bitmap(destWidth, destHeight, PixelFormat.Format24bppRgb);
        bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

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

        grPhoto.DrawImage(imgPhoto,
        new Rectangle(destX, destY, destWidth, destHeight),
        new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight),
        GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }

    public static Image FixedSize(Image imgPhoto, int Width, int Height)
    {
        int sourceWidth = imgPhoto.Width;
        int sourceHeight = imgPhoto.Height;
        int sourceX = 0;
        int sourceY = 0;
        int destX = 0;
        int destY = 0;

        float nPercent = 0;
        float nPercentW = 0;
        float nPercentH = 0;

        nPercentW = ((float)Width / (float)sourceWidth);
        nPercentH = ((float)Height / (float)sourceHeight);

        //if we have to pad the height pad both the top and the bottom
        //with the difference between the scaled height and the desired height
        if (nPercentH < nPercentW)
        {
            nPercent = nPercentH;
            destX = (int)((Width - (sourceWidth * nPercent)) / 2);
        }
        else
        {
            nPercent = nPercentW;
            destY = (int)((Height - (sourceHeight * nPercent)) / 2);
        }

        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap bmPhoto = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
        bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

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

        grPhoto.DrawImage(imgPhoto,
            new Rectangle(destX, destY, destWidth, destHeight),
            new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight),
            GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }

    public static Image Crop(Image imgPhoto, int Width, int Height, AnchorPosition Anchor)
    {
        int sourceWidth = imgPhoto.Width;
        int sourceHeight = imgPhoto.Height;
        int sourceX = 0;
        int sourceY = 0;
        int destX = 0;
        int destY = 0;

        float nPercent = 0;
        float nPercentW = 0;
        float nPercentH = 0;

        nPercentW = ((float)Width / (float)sourceWidth);
        nPercentH = ((float)Height / (float)sourceHeight);

        if (nPercentH < nPercentW)
        {
            nPercent = nPercentW;
            switch (Anchor)
            {
                case AnchorPosition.Top:
                    destY = 0;
                    break;
                case AnchorPosition.Bottom:
                    destY = (int)(Height - (sourceHeight * nPercent));
                    break;
                default:
                    destY = (int)((Height - (sourceHeight * nPercent)) / 2);
                    break;
            }
        }
        else
        {
            nPercent = nPercentH;
            switch (Anchor)
            {
                case AnchorPosition.Left:
                    destX = 0;
                    break;
                case AnchorPosition.Right:
                    destX = (int)(Width - (sourceWidth * nPercent));
                    break;
                default:
                    destX = (int)((Width - (sourceWidth * nPercent)) / 2);
                    break;
            }
        }

        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap bmPhoto = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
        bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

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

        grPhoto.DrawImage(imgPhoto,
            new Rectangle(destX, destY, destWidth, destHeight),
            new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight),
            GraphicsUnit.Pixel);

        grPhoto.Dispose();
        return bmPhoto;
    }

}

regards.

the file format I'm using is : JPEG

Answer 1

This is a normal side-effect of resampling the image with the InterpolationMode set to a high quality value, like Bicubic. This subtly alters the pixel values of just about every pixel, especially since jpeg decompression produces subtle noise in the image. Barely visible to the human eye, quite visible to the resampling filter. Giving the jpeg encoder a much harder time compressing the image. Only starting out with a non-compressed image format, like PNG, can improve the outcome.