Weird resampling when I try to export an Image

Question

Mathematica language newbie here. I wrote the following code to quantize an image:

basepath = "~"
SetDirectory[basepath]
jpgpath = FileNameJoin[{basepath, "jpg"}]
pngpath = FileNameJoin[{basepath, "png"}]

domquant[path_, n_] := 
 Image[{List @@@ 
    DominantColors[Image[ColorQuantize[Import[path], n]], n]}]

(*Convert each jpg in path to its 256-color quantized sample*)
Scan[( \
 img = domquant[#, 24];
    Print[#, " ", img];
Export[
    FileNameJoin[{pngpath, StringJoin[FileBaseName[#], ".jpg"]}],
    img,
    "JPEG", ImageResolution -> 300, 
ImageSize -> {8192, 512}]) &, {FileNames[
"*.jpg", {jpgpath}][[1]]}]

If I change the 24 in the domquant call to a higher value I get what looks like a rasterized image (I think). Specifically, a gradient is applied. For example, here's the result of domquant[#, 256]:

However, if I leave the value as n = 24 or some other smaller number, I get a nice image like this which has discrete boundaries between each value of n, and is actually what I am trying to achieve:

So, why is 24 the magic number beyond which the blur effect takes place? How can I get an image with nice discrete colors using a higher value of n?

In response to Szabolcs, if I remove the ImageResolution and ImageSize options, I get this image:

Not what I'm looking for. I want to create an image like the second one above, where each of 256 colors is represented discretely, and is of arbitrary size.

In response to Simon Woods, if I add Resampling -> "Nearest" to Export, I ge this image with n=256, again blurry:

Thanks to everyone who commented, the following comment from SimonWoods helped me understand. Here's the final (working) code and the resulting (quite beautiful) image.

basepath = "~"
SetDirectory[basepath]
jpgpath = FileNameJoin[{basepath, "jpg"}]
pngpath = FileNameJoin[{basepath, "png"}]

domquant[path_, n_] := 
 Image[{List @@@ 
    DominantColors[Image[ColorQuantize[Import[path], n]], n]}]

(*Convert each jpg in path to its 256-color quantized sample*)
Scan[(
   img = domquant[#, 256];
   img = ImageResize[img, {8152, 512}, Resampling -> "Nearest"];
   Print[#, " ", img];
   Export[
    FileNameJoin[{pngpath, StringJoin[FileBaseName[#], ".png"]}],
        img, "PNG"]) &, {FileNames["*.jpg", {jpgpath}][[1]]}]

Answer 1

To prevent interpolation between adjacent pixels requires the option Resampling -> "Nearest" in ImageResize. This is the default setting for images smaller than $24\times24$ pixels, but larger images will use one of the other resampling methods (I'm not sure which). The desired result can therefore be obtained with:

img = ImageResize[img, {8152,512}, Resampling -> "Nearest"]