Updated readme

README.md

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+
+# Description
+
+Urban is one of the most widely used hyperspectral data used in the hyperspectral unmixing study. There are 307x307 pixels, each of which corresponds to a 2x2 m2 area. In this image, there are 210 wavelengths ranging from 400 nm to 2500 nm, resulting in a spectral resolution of 10 nm. After the channels 1-4, 76, 87, 101-111, 136-153 and 198-210 are removed (due to dense water vapor and atmospheric effects), 162 channels are left (this is a common preprocess for hyperspectral unmixing analyses). There are three versions of ground truth, which contain 4, 5 and 6 endmembers respectively, which are introduced in the ground truth.
+
+# Quick look
+
+<figure>
+    <img src= "assets/D9_1.png" alt="Urban" width="500" />
+    <figcaption>Urban and its ground truths.</figcaption>
+</figure>
+
+
+# Characteristics
+
+Ground Truth: three versions, including 4, 5 and 6 endmembers respectively.
+
+- 4 endmembers version: The 4 endmembers are "#1 Asphalt", "#2 Grass", "#3 Tree" and "#4 Roof" respectively.
+
+- 5 endmembers version: The 5 endmembers are "#1 Asphalt", "#2 Grass", "#3 Tree", "#4 Roof" and "#5 Dirt" respectively.
+
+- 6 endmembers version: The 6 endmembers are "#1 Asphalt", "#2 Grass", "#3 Tree", "#4 Roof", "#5 Metal", and "#6 Dirt" respectively.
+
+# Credits
+
+Dataset originally collected by Feiyun Zhu and originally available at: http://www.escience.cn/people/feiyunZHU/Dataset_GT.html
+
+To use this dataset, cite the associated paper:
+
+```
+@misc{zhu2017hyperspectral,
+      title={Hyperspectral Unmixing: Ground Truth Labeling, Datasets, Benchmark Performances and Survey}, 
+      author={Feiyun Zhu},
+      year={2017},
+      eprint={1708.05125},
+      archivePrefix={arXiv},
+      primaryClass={cs.CV}
+}