C# – Graphics on indexed image

cgraphicsimageindexed-image

I am getting error:

"A Graphics object cannot be created from an image that has an indexed
pixel format."

in function:

public static void AdjustImage(ImageAttributes imageAttributes, Image image)
{
        Rectangle rect = new Rectangle(0, 0, image.Width, image.Height);

        Graphics g = Graphics.FromImage(image);       
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
        g.DrawImage(image, rect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, imageAttributes);
        g.Dispose();
}

I would like to ask you, how can I fix it?

Best Answer

Refering to this, it can be solved by creating a blank bitmap with the same dimensions and the correct PixelFormat and the draw on that bitmap.

// The original bitmap with the wrong pixel format. 
// You can check the pixel format with originalBmp.PixelFormat
Bitmap originalBmp = new (Bitmap)Image.FromFile("YourFileName.gif");

// Create a blank bitmap with the same dimensions
Bitmap tempBitmap = new Bitmap(originalBmp.Width, originalBmp.Height);

// From this bitmap, the graphics can be obtained, because it has the right PixelFormat
using(Graphics g = Graphics.FromImage(tempBitmap))
{
    // Draw the original bitmap onto the graphics of the new bitmap
    g.DrawImage(originalBmp, 0, 0);
    // Use g to do whatever you like
    g.DrawLine(...);
}

// Use tempBitmap as you would have used originalBmp
return tempBitmap;

Related Solutions

Android – Strange OutOfMemory issue while loading an image to a Bitmap object

To fix the OutOfMemory error, you should do something like this:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 8;
Bitmap preview_bitmap = BitmapFactory.decodeStream(is, null, options);

This inSampleSize option reduces memory consumption.

Here's a complete method. First it reads image size without decoding the content itself. Then it finds the best inSampleSize value, it should be a power of 2, and finally the image is decoded.

// Decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
    try {
        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f), null, o);

        // The new size we want to scale to
        final int REQUIRED_SIZE=70;

        // Find the correct scale value. It should be the power of 2.
        int scale = 1;
        while(o.outWidth / scale / 2 >= REQUIRED_SIZE && 
              o.outHeight / scale / 2 >= REQUIRED_SIZE) {
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {}
    return null;
}

C# – How to convert an Indexed pixel format image to a 32-bit image

One easy way is to create a new image of the same size (with a 32-bit pixel format). Then create a graphics object for that image and draw the original on top of it.

Best Answer

Related Solutions

Android – Strange OutOfMemory issue while loading an image to a Bitmap object

C# – How to convert an Indexed pixel format image to a 32-bit image

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