I need to reduce image sizes, while keeping some quality. However, I am accepting GIF, JPEG, JPG and PNG.
The uploading of the image is compleetly functional, and I have been able to scale its width and/or height with sucess.
I found an awesome post here on Stackoverflow, that gave me a very good sample of code:
Image myImage = //... load the image somehow
// Save the image with a quality of 50% SaveJpeg (destImagePath, myImage, 50); //add this! using System.Drawing.Imaging;
/// <summary>
/// Saves an image as a jpeg image, with the given quality
/// </summary>
/// <param name="path">Path to which the image would be saved.</param>
// <param name="quality">An integer from 0 to 100, with 100 being the
/// highest quality</param>
public static void SaveJpeg (string path, Image img, int quality)
{
if (quality<0 || quality>100)
throw new ArgumentOutOfRangeException("quality must be between 0 and 100.");
// Encoder parameter for image quality
EncoderParameter qualityParam =
new EncoderParameter (Encoder.Quality, quality);
// Jpeg image codec
ImageCodecInfo jpegCodec = GetEncoderInfo("image/jpeg");
EncoderParameters encoderParams = new EncoderParameters(1);
encoderParams.Param[0] = qualityParam;
img.Save (path, jpegCodec, encoderParams);
}
/// <summary>
/// Returns the image codec with the given mime type
/// </summary>
private static 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;
}
However, this code seems to work with JPEG images only.
First of all, JPEG uses a "lossy" compression algorithm, which is why you can tune the quality. Lower quality will result better compression at the cost of higher data loss. Also realize that the JPEG format is designed for photograph-like images, and applying JPEG to other types of images can be disappointing (google "jpeg artifacts").
PNG and GIF are lossless, so they can't support a quality parameter. This isn't to say that you can't get better compression out of them - there's a variety of tools to reduce the size of your PNG's (pngcrush, punypng, etc), but these tools (mostly) work in a fundamentally different way than JPEG compressors do. One thing to note is that GIF supports a smaller palette than PNG - only up to 256 colors.
So to answer your questions in order:
Can't really compare, since compression in JPEG comes with a tradeoff while compression in PNG and GIF doesn't, and how tolerable the tradeoff is depends on the type of image. That is, JPEG will often give better compression, but if the image isn't a photograph the result will be noticeably worse.
Your code for JPEG is fine. Google for C#-compatible tools for PNG.
You'll need to experiment with the types of images you expect.
Yes.