Problem with thumbnail

i am having a problem with image uploader.I am making three thumbnail of size 50*50,100*100 and 150*150.

While uploading an image of size 137*76(original value).

I am getting thumbnail size of image as follows:

thumbnail of 50 * 50 as 50*28

thumbnail of 100*100 as 100 * 55

thumbnail of 150*150 as 137 * 76.

Another image i uploaded that was of size 50*25.And got back all thumbnail of an image with size 50 * 25.

Can't i get the size of an image as of thumbnail irrespective of what the size of the image be?and if not would somebody guide me how to get such kind of image size. or any changes ini the uploader that would help me to get desired result.

code(if required):

iu.addParam("UploadThumbnail3FitMode", "Fit");

iu.addParam("UploadThumbnail3Width", "150");

iu.addParam("UploadThumbnail3Height", "150");

iu.addParam("UploadThumbnail3JpegQuality", "60");

iu.addParam("UploadThumbnail3CopyExif", "true");

iu.addParam("UploadThumbnail2FitMode", "Fit");

iu.addParam("UploadThumbnail2Width", "100");

iu.addParam("UploadThumbnail2Height", "100");

iu.addParam("UploadThumbnail2JpegQuality", "60");

//Configure thumbnail settings.

iu.addParam("UploadThumbnail1FitMode", "Fit");

iu.addParam("UploadThumbnail1Width", "50");

iu.addParam("UploadThumbnail1Height", "50");

iu.addParam("UploadThumbnail1JpegQuality", "60");

Please help to resolve the problem.Thank u.