Opencv – How to save an Emgu `Image frame` in a memory stream as JPEG

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How can I save an Emgu Image<Bgr, Byte> frame in a memory stream as JPEG?

Best Answer

You have two options the first is the native EMGU images.save("filename"); method however the quality is not great and lossy. The best method is to use the following c# method.

This is the function is saveJpeg(SaveFile.FileName, img.ToBitmap(), 100);. Based on the method saveJpeg(string path, Bitmap img, long quality).

using System.Drawing.Imaging;

private void saveJpeg(string path, Bitmap img, long quality)
{
    // Encoder parameter for image quality

    EncoderParameter qualityParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);

    // Jpeg image codec
    ImageCodecInfo jpegCodec = this.getEncoderInfo("image/jpeg");

    if (jpegCodec == null)
    return;

    EncoderParameters encoderParams = new EncoderParameters(1);
    encoderParams.Param[0] = qualityParam;

    img.Save(path, jpegCodec, encoderParams);
}

private ImageCodecInfo getEncoderInfo(string mimeType)
{
    // Get image codecs for all image formats
    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

    // Find the correct image codec
    for (int i = 0; i < codecs.Length; i++)
    if (codecs[i].MimeType == mimeType)
    return codecs[i];
    return null;
}

hope this helps,

Cheers,

Chris

Related Solutions

How to create Emgu Image from System.Drawing.Image

You can first convert System.Drawing.Image object to a Bitmap and then create an Emgu.CV.Image with that bitmap. The code is as follows:

System.Drawing.Image image;
Bitmap bmpImage = new Bitmap(image);
Emgu.CV.Image = new Emgu.CV.Image<Bgr, Byte>(bmpImage);

Better, if you have a memory stream, you can get a bitmap directly from the memory stream

MemoryStream ms;
Bitmap bmpImage = new Bitmap(ms);
Emgu.CV.Image = new Emgu.CV.Image<Bgr, Byte>(bmpImage);

How to extract a good quality JPEG image from a video file with ffmpeg

Use `-qscale:v` to control quality

Use -qscale:v (or the alias -q:v) as an output option.

Normal range for JPEG is 2-31 with 31 being the worst quality.
The scale is linear with double the qscale being roughly half the bitrate.
Recommend trying values of 2-5.
You can use a value of 1 but you must add the -qmin 1 output option (because the default is -qmin 2).

To output a series of images:

ffmpeg -i input.mp4 -qscale:v 2 output_%03d.jpg

See the image muxer documentation for more options involving image outputs.

To output a single image at ~60 seconds duration:

ffmpeg -ss 60 -i input.mp4 -qscale:v 4 -frames:v 1 output.jpg

To continuously overwrite/update/save to a single image

Use -update 1 image muxer option. Example for once per second from a live streaming input:

ffmpeg -i rtmp://input.foo -q:v 4 -r 1 -update 1 output.jpg