WPF BitmapImage分为两部分

Question

I'm messing about with Bitmaps in a WPF application. I receive the a byte array on a background thread and a converter changes it to a bitmapSource for binding.

However, if I try to directly create the bitmapSource in memory and display it, it splits the image into two. I'm haven't had a great deal of experience with bitmaps but enough so that I could always display images.

The weird thing, is that if I write the file out first, then read it back in, it works.

File.WriteAllBytes(@"C:\woot2.bmp", bytes);

var bmp = new BitmapImage(new Uri(@"C:\woot2.bmp"));
var height = bmp.Height;                       // 480.0
var width = bmp.Width;                         // 640.0
var format = bmp.Format;                       // Indexed8
var dpix = bmp.DpiX;                           // 96.0
var dpiY = bmp.DpiY;                           // 96.0
var pallete = bmp.Palette;                     // Gray256
var cacheOption = bmp.CacheOption;             // Default
var createOptions = bmp.CreateOptions;         // None
return bmp;

[

I've checked the height, width, pixelFormat, pixelPalette, dpi etc all match the file that I read in and it still displays it incorrectly. Even checked the header of the file.

I've tried BitmapImages, BitmapSources, WriteableBitmaps with PngBitmapEncoder and I still get the same. I feel like either i'm missing something fundamental or there's a bug. I thought the slice was wrong, but there's no skewing,

i'm displaying it in an image:

<Image Width="640" Height="480" 
     Source="{Binding VisionImage, Mode=OneWay,UpdateSourceTrigger=PropertyChanged, 
     Converter={StaticResource VisionImageConverter} }"></Image>

Here's the code i've got to convert it currently

var width = 640;
var height = 480;
var dpiX = 96;
var dpiY = 96;
var pixelFormat = PixelFormats.Indexed8;
var palleteFormat = BitmapPalettes.Gray256;
var stride = 4* (((width*pixelFormat.BitsPerPixel) + 31)/32);
return  BitmapSource.Create(width, height, dpiX, dpiY, 
                       pixelFormat, palleteFormat, bytes, stride);

Any ideas?

Answer 1

Apparently the byte array does not contain raw pixel data, but an encoded BMP buffer, so you can't create a BitmapSource by BitmapSource.Create .

You should instead create a BitmapImage from the encoded BMP buffer like this:

var bitmapImage = new BitmapImage();
using (var stream = new MemoryStream(bytes))
{
    bitmapImage.BeginInit();
    bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
    bitmapImage.StreamSource = stream;
    bitmapImage.EndInit();
}

Or alternatively create a BitmapFrame like this:

BitmapFrame bitmapFrame;
using (var stream = new MemoryStream(bytes))
{
    bitmapFrame = BitmapFrame.Create(stream,
        BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
}

Answer 2

Okay, so the answer for this ended up being quite simple. Instead of giving it just the pixel array, I was giving it the whole bitmap file array. I think when you create a bitmapImage from a file it must use a bitmapDecoder internally. Which is why writing to a file and then reading it back worked.

So I could have calculated the pixel offset from the file and then copied the bytes that I needed, but I chose to wrap the array in a memorystream and use a BmpBitmapDecoder because it was simpler

using(var ms = new MemoryStream(bytes))
{
     var decoder = new BmpBitmapDecoder(ms, BitmapCreateOptions.DelayCreation, BitmapCacheOption.OnDemand);
     return new WriteableBitmap(decoder.Frames.FirstOrDefault());
}