Resize a an image (its actual kb/mb size) in c#`

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This is the code I am using to resize an image (the actual kb/mb size)

C#

public static System.Drawing.Image ScaleImage(System.Drawing.Image image, int maxHeight)
    {
        var ratio = (double)maxHeight / image.Height;
        var newWidth = (int)(image.Width * ratio);
        var newHeight = (int)(image.Height * ratio);
        var newImage = new Bitmap(newWidth, newHeight);

        using (var g = Graphics.FromImage(newImage))
        {
            g.DrawImage(image, 0, 0, newWidth, newHeight);
        }
        return newImage;
    }

But when I use this code, it actually makes the image size(kb size) bigger than what it was. Although the physical size (width x height) is smaller.
Where am I going wrong?

Posted 13-Dec-13 0:10am

Member 10395722

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Mitchell J. 13-Dec-13 6:16am

What example sizes are in play here? What file types are causing the issue?

Member 10395722 17-Dec-13 7:21am

For example a file of 90Kb after resize is 171Kb and the file type I am using is JPEG

BillWoodruff 13-Dec-13 6:46am

You are creating a new image with a format of 32 bits-per-pixel ARGB: your source image probably has less bit-depth. So, file size is larger.

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OriginalGriff · Answer 1 · 2013-12-13T00:22:00

Solution 1

The first thing to do is look at your numbers: put a breakpoint on the line:

C#

var newImage = new Bitmap(newWidth, newHeight);

and use the debugger to examine newHeight, newWidth, and ratio
I suspect that they will not be what you expect.

Have you considered what happens in your current image has a lower height than maxHeight?

BTW: How do you know the kb / mb size is bigger? Are you saving the new image and comparing file sizes? If so, are they the same type of file, and an uncompressed format?

Posted 13-Dec-13 0:22am

OriginalGriff

Comments

Member 10395722 17-Dec-13 7:15am

I was saving the files in folders and then comparing the file sizes. They are the same file type and very sure they are uncompressed since I don't compress it anywhere.

OriginalGriff 17-Dec-13 7:23am

Doesn't matter if you don't compress them: some file types always contain compressed data.
JPG for example uses a "lossy" compression technique to reduce file size - depending on what application a JPG file is written with the amount of compression can be very different.
When you resize an image (even if you reduce the size) you can end up with a bigger file because the data being compressed is different!

Similarly, even if your file type is BMP which isn;t compressed, if the original image is 8 bits per pixel and the new images is 32 bits (normally for .NET) then the new, smaller resolution file can easily be bigger than the original!

CPallini · Answer 2 · 2013-12-13T00:24:00

Solution 2

You should check that the PixelFormat of the original image and of the resized one are the same (see, for instance: Bitmap Constructor (Int32, Int32, PixelFormat)[^]).

Posted 13-Dec-13 0:24am

CPallini

Member 10395722 · Answer 3 · 2013-12-17T01:20:00

I decided to use the current code that I have. What I observed is that bigger images for example 2MB gets resized to a smaller KB Size and smaller images of 80KB get bigger.

What BillWoodruff said in a comment is probably what is happening here. I don't know if there is a fix for this but for now i'll use it as is because it makes very big files atleast a little bit smaller

agent_kruger · Answer 4 · 2013-12-18T04:03:00

Solution 4

try saving in png extension because that compacts some image automatically.

Posted 18-Dec-13 4:03am

agent_kruger