I have a PNG file which has 8-bit color depth as evidenced by file properties:
Yes, when I open the file
var filePath = "00050-w600.png";
var bitmap = new Bitmap(filePath);
Console.WriteLine(bitmap.PixelFormat);
I get Format32bppArgb. I also looked in the PropertyIdList and PropertyItems properties but didn't see anything obvious.
So how do I extract the Bit Depth from the PNG?
P.S. None of the framework methods seem to work. System.Windows.Media.Imaging.BitmapSource might work but it's only in WPF and .NET Core 3. I need this for .NET 4.x and .NET Core 2.x.
P.P.S. I just needed to know whether the PNG is 8 bit or not, so I wrote a sure fire method to check if anyone needs it - should work in any framework.
public static bool IsPng8BitColorDepth(string filePath)
{
const int COLOR_TYPE_BITS_8 = 3;
const int COLOR_DEPTH_8 = 8;
int startReadPosition = 24;
int colorDepthPositionOffset = 0;
int colorTypePositionOffset = 1;
try
{
using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
{
fs.Position = startReadPosition;
byte[] buffer = new byte[2];
fs.Read(buffer, 0, 2);
int colorDepthValue = buffer[colorDepthPositionOffset];
int colorTypeValue = buffer[colorTypePositionOffset];
return colorDepthValue == COLOR_DEPTH_8 && colorTypeValue == COLOR_TYPE_BITS_8;
}
}
catch (Exception)
{
return false;
}
}
Color Allowed Interpretation
Type Bit Depths
0 1,2,4,8,16 Each pixel value is a grayscale level.
2 8,16 Each pixel value is an R,G,B series.
3 1,2,4,8 Each pixel value is a palette index;
a PLTE chunk must appear.
4 8,16 Each pixel value is a grayscale level,
followed by an alpha channel level.
6 8,16 Each pixel value is an R,G,B series,
followed by an alpha channel level.
