Export an image at 1000 dpi

I'm trying to export an image at 1000 dpi. The author guide of a lot of papers wants this resolution! Then I must to import this image in Word in a small box; let's say 7x4 cm. This is the code that I made and the relative image:

grayColorList = (Blend[{Black, White}, #] & /@ Range[0, 1, 0.1]);
histogram =
Labeled[Histogram[{dataBr[[All, 1]], datacl[[All, 1]],
dataFCl[[All, 1]], dataF[[All, 1]]}, ChartLayout -> "Stacked",
ChartLegends -> {"Br-derivatives", "Cl-derivatives",
"F+Cl+Br-derivatives", "F-derivatives"},
ChartStyle -> {grayColorList[[1]], grayColorList[[4]],
grayColorList[[7]], grayColorList[[9]]}], {Rotate[
Style["Relative Frequency", 12], 90 Degree],
"\!$$\*SubscriptBox[\(\[Lambda]$$, $$Exp$$]\)"}, {Left, Bottom},
FrameMargins -> {{-8, 0}, {0, 0}}]

This is a very nice image, but when I try to Export it

Export["Histogram.Tif", histogram, ImageResolution -> 1000]

This is the result:

And this is very ugly image! I've read the other similar posts but I can't find the answer. Thanks in advance.

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You need to set a specific ImageSize for your graphics. –  rm -rf Feb 18 at 22:05
If i understand this all correctly, you essentially need an image that is 2756x1575 pixels in size. –  chuy Feb 18 at 23:05