将互操作颜色转换为System.Drawing.Color

Question

I am looking how to convert Microsoft.Office.Interop.Word/Excel/PowerPoint.Color to System.Drawing.Color in C#.

I have found the contrary in this forum here or here but I don't find how to convert from Interop Color to System.Drawing.Color.

I have understood that Interop color is expressed in RGB considering:

RGBvalue = Red + 256*Green + 256*256*Blue

but it is not very easy from a RGBvalue to find the value of Red Green Blue (for example if the value is 5652 I don't know how to find Red is 20 and Green is 22).

Do you know a function to convert Microsoft.Office.Interop.Word/Excel/PowerPoint.Color to System.Drawing.Color (or to OLE and then, I know how to convert) ?

Answer 1

This is all much simpler if you look at the data in hexadecimal format. 5652 becomes 0x1614, which is clearly bytes 0x16 and 0x14. Or, 0x16 * 0x100 + 0x14 .

The opposite of multiplying with 0x100 should simply be dividing it by 0x100, but to actually cut off the excess, I advise using the AND bit operation.

AND will keep only the bits that are common in both values, so, in binary representation, to keep only the lowest 8 bits, you need to AND it with a value with all 8 bits enabled, which would be 0xFF. The AND between 0x1614 (your "5652" example) and 0xFF, viewed in binary format, would go like this:

00010110 00010100
00000000 11111111
v------AND------v
00000000 00010100

As you see, it effectively cuts off everything higher than the lowest byte, resulting in 00010100b, or 0x14, or 20.

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For dividing by multiples of 2, there is another bit operation that is very handy and really efficient: bit shifting. 0x100 is actually '1', shifted up by 8 bits. So to get the original value back, it just needs to be shifted down by 8 bits.

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if your colour is B * 0x10000 + G * 0x100 + R , then to reverse it:

public static Color GetColorFromInterop(Int32 val)
{
    // Limit to a value containing only the bits in 0xFF
    Int32 r = val & 0xFF;
    // Shift down by 8 bits (meaning, divide by 0x100), then limit to 0xFF
    Int32 g = (val >> 8) & 0xFF;
    // Shift down by 16 bits (meaning, divide by 0x10000), then limit to 0xFF
    Int32 b = (val >> 16) & 0xFF;
    return Color.FromArgb(r, g, b);
}