Commented Unassigned: Performance problem with group4 conversion [1226]

Hi,

I've detected some performance problem with fax group4 conversion, here I'll try to describe how to reproduce it:

From terminal I execute the command what takes about ( 3-5 seconds )
convert -threshold 80% -compress group4 C:\Users\DXD\Pictures\OKMSc
an\Images\2014-5-6\Scanned-1.jpeg C:\Users\DXD\Pictures\OKMScan\Images\2014-5-6\
Scanned-2.jpeg C:\Users\DXD\Pictures\OKMScan\Images\2014-
5-6\pdf4.pdf

But when I try same action from my source code it takes several minutes ( more than 3 minutes ), here's mu method
public void convertToPdf(List<String> pathList, int percentage)
{
int number = 0;
if (pathList != null && pathList.Count > 0)
{
if (!existFolder(destPath + folderRoot, folderName))
{
createFolder(destPath + folderRoot, folderName);
}
number = findLastFile(destPath + folderRoot + folderName) + 1;
using (MagickImageCollection collection = new MagickImageCollection())
{
foreach (var path in pathList)
{
MagickImage image = new MagickImage(path);
image.Threshold(percentage);
image.CompressionMethod = CompressionMethod.Group4;
collection.Add(image);
}
collection.Write(destPath + folderRoot + folderName + "\\" + fileName + "-" + number.ToString() + ".pdf");
}
}
}

To execute simply provide a list of file paths. The method takes a lot of time in line collection.Write

Note: I'm trying with 5 color jepg files with about 900kb and 3307x4677px
Comments: ** Comment from web user: pherrera **

Additional information:
With images with equal or less 300 dpi seems goes right, but with 600 dpi or upper gets this kind of problem.