Using Image Magick Versus GD For Image Conversion
This is a comparison of image quality using GD version 1 vs. the Image Magick vs. GD version 2 using Qdig's image conversion parameters. This image was selected because it has the blue sky, which emphasizes the weakness of GD1. For some images the difference would not be nearly as obvious.
The original image is 1400x1050 pixels and occupies 334KB of disk space. The resampled images are 600x450 pixels (Qdig's "Medium" size for an image with that width:height ratio).
An Image Converted With GD1
The file size of this image is 86.7KB.
The sky is a bit spotty and the sign post has some noticable distortion.
The Same Image Converted with Image Magick (Qdig Parameters)
The file size of this image is 69.6KB.
The file size of the IM-converted image is smaller and the difference in quality is quite noticable. Image Magick, using the Qdig default parameters for a medium-sized image, has done an excellent job resampling the original.
The Same Image Converted With GD2
The file size of this image is 60.4KB.
This image is noticably softer than the IM image. This would possibly explain the smaller file size.