Why Does Saving a JPEG to a MemoryStream in GDI Throw a 'Generic Error'?

Save JPEG in GDI to the memory flow

When using GDI to save JPEG images into memory flow, it will cause abnormalities. This problem is particularly puzzling because it occurs on JPEG and GIF images, but it will not occur on PNG images.

Analysis of the cause

The reason for this error is that the memory flow must be opened when saving the image object. This is because the object is created with flow, and the data will be refreshing only when the flow is turned off.

Solution

To solve this problem, make sure that the memory flow is kept open before the image is completely preserved. The following code fragment demonstrates the correct method:

Interpretation of error information

<code class="language-csharp">using (var ms = new MemoryStream())
{
    using (Image image = new Bitmap(...))
    {
        ImageFormat format;
        switch (image.RawFormat) // 使用 RawFormat 代替 MimeType()
        {
            case ImageFormat.Png:
                format = ImageFormat.Png;
                break;
            case ImageFormat.Gif:
                format = ImageFormat.Gif;
                break;
            default:
                format = ImageFormat.Jpeg;
                break;
        }

        image.Save(ms, format);
        return ms.ToArray();
    }
}</code>

The vague news "GM in GDI" confuses many developers. However, the reason for this vagueness is that the abnormalities are not triggered by the GDI itself, but caused by the system COM interoperable layer.

alternative

If the memory stream cannot be kept during the image preservation process, another solution is to create a new memory flow from the original memory flow before preservation:

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