How to convert approximate white to transparent background

Question

I am trying to convert the image into png transparent image, but it is not convert exactly, because I can see as white but it is not exact white(255), the value is like (#FBFBFF,#F7FFFF,etc...) how can I handle this?

The Image is coming like https://i.stack.imgur.com/CbSwe.png

I am trying like below

    public static Bitmap MakeTransparent(Image image)
    {
        Bitmap b = new Bitmap(image);            
        Color redColor = Color.FromArgb(255, 255, 255);
        Color redColor1 = Color.FromArgb(254, 254, 254);
        Color redColor2 = Color.FromArgb(253, 253, 253);
        Color redColor3 = Color.FromArgb(252, 252, 252);
        Color redColor4 = Color.FromArgb(251, 251, 251);
        Color redColor5 = Color.FromArgb(250, 250, 250);
        Color redColor6 = Color.FromArgb(249, 249, 249);
        Color redColor7 = Color.FromArgb(249, 249, 248);


        b.MakeTransparent(redColor);
        b.MakeTransparent(redColor1);
        b.MakeTransparent(redColor2);
        b.MakeTransparent(redColor3);
        b.MakeTransparent(redColor4);
        b.MakeTransparent(redColor5);
        b.MakeTransparent(redColor6);
        b.MakeTransparent(redColor7);


        return b;
    }

but no use.

score 4 · Accepted Answer · answered Mar 06 '15 at 08:58

If you replace all near-white colours with white, you can then make just the white itself transparent:

    public static Bitmap MakeTransparent(Image image)
    {
        Bitmap b = new Bitmap(image);

        var replacementColour = Color.FromArgb(255, 255, 255);
        var tolerance = 10;

        for (int i = b.Size.Width - 1; i >= 0; i--)
        {
            for (int j = b.Size.Height - 1; j >= 0; j--)
            {
                var col = b.GetPixel(i, j);

                if (255 - col.R < tolerance && 
                    255 - col.G < tolerance && 
                    255 - col.B < tolerance)
                {
                    b.SetPixel(i, j, replacementColour);
                }
            }
        }

        b.MakeTransparent(replacementColour);

        return b;
    }

aush · Answer 2 · 2015-03-06T08:58:32.437

0

foreach (var color in GetColors(10))
{
    b.MakeTransparent(color);
}

IEnumerable<Color> GetColors(int interval)
{
    for (var r = 255; r > 255 - interval; --r)
    {
        for (var g = 255; g > 255 - interval; --g)
        {
            for (var b = 255; b > 255 - interval; --b)
            {
                yield return Color.FromArgb(r, g, b);
            }
        }
    }

    // Or
    //return from r in Enumerable.Range(255 - interval, interval)
    //       from g in Enumerable.Range(255 - interval, interval)
    //       from b in Enumerable.Range(255 - interval, interval)
    //       select Color.FromArgb(r, g, b);
}

edited Mar 06 '15 at 08:58

answered Mar 06 '15 at 08:47

aush

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Very hoot Thank you, but it is very slow execution – Mar 06 '15 at 08:57
Speed up hints can be found [here](http://stackoverflow.com/questions/15297320/change-a-bitmaps-pixel-colour) – Mikael Mar 06 '15 at 09:12
The above one is very high speed. – Mar 06 '15 at 09:13

How to convert approximate white to transparent background

2 Answers2