CoreML frameworks generated different results from coremltools

Hi everyone in this forum,

I have been developing image recognition app in ios 11 following the CoreML examples. However i notice that there is difference of the results when calling the model in ios, and the ones using coremltools in mac/python. I think the difference may lie on the image loading part. Python code use Pillow to load image, but xcode use CoreImage. I pasted the key codes as below. Hopefully somebody can help to point out the issue.

Also the input image is a 299*299 jpg. So should not any resizing happened in either of the implementation. Thank you.

################

## python codes ##

################

import coremltools
from PIL import Image
from keras.preprocessing import image
import numpy as np

IMG_PATH='./test.jpg'
img = image.load_img(IMG_PATH)
model=coremltools.models.MLModel("./Inceptionv3.mlmodel")
res = model.predict({'image':img})

##############

## ios codes . ##

##############

    self.image = [CIImage imageWithContentsOfURL:fileURL];
    self.model = [[[Inceptionv3 alloc] init] model];

    VNCoreMLModel *m = [VNCoreMLModel modelForMLModel: self.model error:nil];
    VNCoreMLRequest *rq = [[VNCoreMLRequest alloc] initWithModel: m completionHandler: (VNRequestCompletionHandler) ^(VNRequest *request, NSError *error){
        NSArray *results = [request.results copy];
        NSString *top_results = @"";
        for(int index = 0; index < kNumResults; index++)
        {
            VNClassificationObservation *res = ((VNClassificationObservation *)(results[index]));
             NSString *tmp = [top_results stringByAppendingFormat: @"- %d %.4f %@\n ", index, res.confidence,res.identifier];
             top_results = [tmp copy];
        }
        self.label_prob = [top_results copy];
    }];

    NSDictionary *d = [[NSDictionary alloc] init];
    NSArray *a = @[rq];
    VNImageRequestHandler *handler = [[VNImageRequestHandler alloc] initWithCIImage:self.image options:d];

    dispatch_queue_t myCustomQueue;
    myCustomQueue = dispatch_queue_create("com.example.MyCustomQueue", NULL);

    dispatch_sync(myCustomQueue, ^{
        [handler performRequests:a error:nil];
    });