生成低位深度的图像文件？

Question

生成低位深度的图像文件？

c#vb.netbitmapimaging

11

bpp是每像素位数，所以32bpp意味着R/G/B/A的值为8/8/8/8。

就像.NET中有一个枚举用于表示这些“System.Drawing.Imaging.PixelFormat”。

现在，一旦我有了包含我的图形的 Bitmap 或 Image 对象，我该如何将其保存到文件中，我应该使用什么格式？

哪种图像文件格式（JPEG/GIF/PNG）支持低位深度，例如16bpp或8bpp (而非通常的32bpp或24bpp)

- Jeremy Rudd

这里有另一种方法，可以查看此链接：(https://stackoverflow.com/a/21741170/1024754) - antonio

5个回答

1

每像素一位

这是从.Net中产生最小可能的PNG格式。请注意，它是黑白的 - 甚至不是灰度。对于文档非常有用。

使用者代码：

Dim src = (the original bitmap)
Using img = New Bitmap(src.Width, src.Height, PixelFormat.Format16bppRgb555) ' Provided Make1bpp function requires this
  img.SetResolution(src.HorizontalResolution, src.VerticalResolution)
  Using g = Graphics.FromImage(img)
    g.Clear(Color.White) ' remove transparancy
    g.DrawImage(src, 0, 0, src.Width, src.Height)
  End Using

  Using img2 As Bitmap = Make1bpp(img)
    img2.SetResolution(src.HorizontalResolution, src.VerticalResolution)

    Dim myencoder = (From parm In ImageCodecInfo.GetImageEncoders() Where parm.MimeType = "image/png").First()
    Dim encoderParams = New EncoderParameters(1)
    encoderParams.Param(0) = New EncoderParameter(Encoder.ColorDepth, 8L)
    If IO.File.Exists(pngName) Then
      IO.File.Delete(pngName)
    End If
    img2.Save(pngName, myencoder, encoderParams)
  End Using
End Using

Make1bpp

这是PNG编码器关心的内容。

Function Make1bpp(ByVal bmpIN As Bitmap) As Bitmap
    Dim bmpOUT As Bitmap
    bmpOUT = NewBitmap(bmpIN.Width, bmpIN.Height, PixelFormat.Format1bppIndexed)
    bmpOUT.SetResolution(bmpIN.HorizontalResolution, bmpIN.VerticalResolution)

    ' seems like I've got this crap in this program about 100x.
    If bmpIN.PixelFormat <> PixelFormat.Format16bppRgb555 Then
      Throw New ApplicationException("hand-coded routine can only understand image format of Format16bppRgb555 but this image is " & _
        bmpIN.PixelFormat.ToString & ". Either change the format or code this sub to handle that format, too.")
    End If

    ' lock image bytes
    Dim bmdIN As BitmapData = bmpIN.LockBits(New Rectangle(0, 0, bmpIN.Width, bmpIN.Height), _
        Imaging.ImageLockMode.ReadWrite, bmpIN.PixelFormat)
    ' lock image bytes
    Dim bmdOUT As BitmapData = bmpOUT.LockBits(New Rectangle(0, 0, bmpOUT.Width, bmpOUT.Height), _
        Imaging.ImageLockMode.ReadWrite, bmpOUT.PixelFormat)

    ' Allocate room for the data.
    Dim bytesIN(bmdIN.Stride * bmdIN.Height) As Byte
    Dim bytesOUT(bmdOUT.Stride * bmdOUT.Height) As Byte
    ' Copy the data into the PixBytes array. 
    Marshal.Copy(bmdIN.Scan0, bytesIN, 0, CInt(bmdIN.Stride * bmpIN.Height))
    ' > this val = white pix. (each of the 3 pix in the rgb555 can hold 32 levels... 2^5 huh.)
    Dim bThresh As Byte = CByte((32 * 3) * 0.66)
    ' transfer the pixels
    For y As Integer = 0 To bmpIN.Height - 1
      Dim outpos As Integer = y * bmdOUT.Stride
      Dim instart As Integer = y * bmdIN.Stride
      Dim byteval As Byte = 0
      Dim bitpos As Byte = 128
      Dim pixval As Integer
      Dim pixgraylevel As Integer
      For inpos As Integer = instart To instart + bmdIN.Stride - 1 Step 2
        pixval = 256 * bytesIN(inpos + 1) + bytesIN(inpos) ' DEPENDANT ON Format16bppRgb555
        pixgraylevel = ((pixval) And 31) + ((pixval >> 5) And 31) + ((pixval >> 10) And 31)
        If pixgraylevel > bThresh Then ' DEPENDANT ON Format16bppRgb555
          byteval = byteval Or bitpos
        End If
        bitpos = bitpos >> 1
        If bitpos = 0 Then
          bytesOUT(outpos) = byteval
          byteval = 0
          bitpos = 128
          outpos += 1
        End If
      Next
      If bitpos <> 0 Then ' stick a fork in any unfinished busines.
        bytesOUT(outpos) = byteval
      End If
    Next
    ' unlock image bytes
    ' Copy the data back into the bitmap. 
    Marshal.Copy(bytesOUT, 0, _
        bmdOUT.Scan0, bmdOUT.Stride * bmdOUT.Height)
    ' Unlock the bitmap.
    bmpIN.UnlockBits(bmdIN)
    bmpOUT.UnlockBits(bmdOUT)
    ' futile attempt to free memory.
    ReDim bytesIN(0)
    ReDim bytesOUT(0)
    ' return new bmp.
    Return bmpOUT
  End Function

- FastAl

0

所有的图像格式都有效地支持低位深度。如果不需要，您可以将最后几位留空。GIF仅支持低色彩；您只能使用256种颜色。

- MSalters

0

试试这个：

ImageCodecInfo pngCodec = ImageCodecInfo.GetImageEncoders().Where(codec => codec.FormatID.Equals(ImageFormat.Png.Guid)).FirstOrDefault();
if (pngCodec != null)
{
    EncoderParameters parameters = new EncoderParameters();
    parameters.Param[0] = new EncoderParameter(Encoder.ColorDepth, 8);
    myImage.Save(myStream, pngCodec, parameters);
}

- Vojislav Stojkovic

5

PNG编解码器似乎没有使用Encoder.ColorDepth参数。 - psaxton

-1

未经测试的代码 -

Image myImage = new Image();
EncoderParameters parameters = new EncoderParameters(1);   
parameters.Param[0] = new EncoderParameter(Encoder.ColorDepth, 8);
myImage.Save(somestream, ImageFormat.Png, parameters);

看看 System.Drawing.Imaging 命名空间并尝试使用 Encoder.xxx 参数设置和 image.Save 方法。希望对你有所帮助。

更新：如果您想要一个小的图像（低字节数），可以尝试保存为 JPEG 并使用 Encoder.Compression 压缩但会降低图像质量成本。

- Ian Quigley

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Rick Minerich · Accepted Answer

我认为其他回答者没有测试他们的代码，因为GDI+ PNG不支持Encoder.BitDepth EncoderParameter。实际上，唯一支持它的编解码器是TIFF。

在保存图像之前，您需要更改图像的PixelFormat以产生输出的效果。但这并不总是会产生您期望的像素格式。有关哪些像素格式会转化成什么的更多信息，请参见我的这篇文章。

至于PixelFormat的转换，可以使用以下代码：

private Bitmap ChangePixelFormat(Bitmap inputImage, PixelFormat newFormat)
{
  Bitmap bmp = new Bitmap(inputImage.Width, inputImage.Height, newFormat);
  using (Graphics g = Graphics.FromImage(bmp))
  {
    g.DrawImage(inputImage, 0, 0);
  }
  return bmp;
}

不幸的是，这些转换可能会产生一些非常糟糕的输出。特别是在执行有损转换（高位深度到低位深度）的情况下，这一点尤为明显。