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POResizing Image Quality Reduction
 

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  1. POResizing Image Quality Reduction
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    <p>I have written a simple PhotoEditor helper class to downscale and crop images uploaded to my website. Everything is working but I am seeing unsatisfactory quality when the image is saved to file. I have read up on the different settings you can tweak below is my setup for resizing, cropping is identical.</p> <pre><code> public Image ResizeImage(Image imgToResize, Size size) { int sourceWidth = imgToResize.Width; int sourceHeight = imgToResize.Height; float nPercentW = (size.Width/(float) sourceWidth); float nPercentH = (size.Height/(float) sourceHeight); float nPercent = nPercentH &lt; nPercentW ? nPercentH : nPercentW; var destWidth = (int) (sourceWidth*nPercent); var destHeight = (int) (sourceHeight*nPercent); var src = imgToResize; using (var dst = new Bitmap(destWidth, destHeight, imgToResize.PixelFormat)) { dst.SetResolution(imgToResize.HorizontalResolution, imgToResize.VerticalResolution); using (var g = Graphics.FromImage(dst)) { var mime = GetMimeType(imgToResize); ImageFormat format; if (mime == "image/gif" || mime == "image/png") { //convert all gif to png, better resize quality g.SmoothingMode = SmoothingMode.AntiAlias; g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.DrawImage(src, 0, 0, dst.Width, dst.Height); format = ImageFormat.Png; } else { //jpeg g.CompositingQuality = CompositingQuality.HighQuality; g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.SmoothingMode = SmoothingMode.HighQuality; g.PixelOffsetMode = PixelOffsetMode.HighQuality; format = ImageFormat.Jpeg; } g.DrawImage(src, 0, 0, dst.Width, dst.Height); // At this point the new bitmap has no MimeType // Need to output to memory stream var m = new MemoryStream(); dst.Save(m, format); var img = Image.FromStream(m); return img; } } } </code></pre> <p>As you can see I am using the suggested settings for Interpolation, Smoothing etc. I am also saving the jpeg with quality 100.</p> <p>The resultant image has noticeable blurring and artefacts even when resizing down to a modest 75% of its original size. I looked around and this is the recommended way. I found a simplistic way to resize and decided to give that a go.</p> <pre><code>Bitmap NewImg = new Bitmap(original, new Size(387,257)); editor.SaveImage(@"C:\simpleResize.jpg", NewImg, ImageFormat.Jpeg); </code></pre> <p>Surprisingly this produces a much nicer image although it is quite a bit bigger ~30% larger in memory footprint.</p> <p>My question is, what's the difference and what setting am I missing on my resize routine that could account for the uglier result. Id like to get my resize routine to produce the exact same result as the simple resize.</p> <p>Your help is much appreciated. This is my first foray into image processing.</p> <p><strong>EDIT</strong></p> <p>Simple Resize (82KB)</p> <p><a href="http://img189.imageshack.us/img189/2137/simpleresize.jpg" rel="nofollow noreferrer">simple http://img189.imageshack.us/img189/2137/simpleresize.jpg</a></p> <p>My Resize (55KB)</p> <p><a href="http://img12.imageshack.us/img12/4023/complexresize.jpg" rel="nofollow noreferrer">complex http://img12.imageshack.us/img12/4023/complexresize.jpg</a></p>
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    1. USmadcapnmckay
    1. USmadcapnmckay
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    1. COThe dst.Save(m, format); looks like your problem. You're encoding it as jpeg there, with default quality (not 100%), then immediately decoding it back to an image. dst is already an Image (Bitmap class inherits from Image), so you can just return it as-is.
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      1. POResizing Image Quality Reduction
      1. USDavid
    2. COHi David. You were right. My reasoning behind that step was so that the mimetype was part of the resultant image. I store the image in the session temporarily and wanted to be able to retrieve it later. If you update your answer ill mark it as answered.
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