A. Wound Image Analysis System Overview
Our quantitativewound assessment system consists of several
functional modules including wound image capture, wound image
storage, wound image preprocessing, wound boundary determination,
wound analysis by color segmentation and wound
trend analysis based on a time sequence of wound images for a
given patient.All these processing steps are carried out solely by
the computational resources of the smartphone. The functional
diagram of our quantitative wound assessment system is shown
as in Fig. 1 and explained later. Note that the words highlighted
in italics in the text correspond to specific blocks in figures
with block diagrams. While the image capture is the first step
in the flowchart, the image capture box is not one of the image
processing steps and is therefore presented later in Section IV.
A Nexus 4 smartphone was chosen due to its excellent
CPU+GPU performance and high-resolution camera. Although
there are likely performance variations across the cameras
of modern smartphones, such a study was considered
beyond the scope of this paper. After the wound image is captured,
the JPEG file path of this image is added into a wound
image database. This compressed image file, which cannot be
processed directly with our main image processing algorithms,
therefore needs to be decompressed into a 24-bit bitmap file
based on the standard RGB color model. In our system, we use
the built-in APIs of the Android smartphone platform to accomplish
the JPEG compression and decompression task. The
“image quality” parameter was used to control the JPEG compression
rate. Setting “image quality” to 80 was shown empirically
to provide the best balance between quality and storage
space. For an efficient implementation on the smartphone alone,
no method was used to further remove the artifacts introduced
by JPEG lossy compression.
In the Image preprocessing step, we first downsample the
high-resolution bitmap image to speed up the subsequent image
analysis and to eliminate excessive details that may complicate
wound image segmentation. In our case, we downsample
the original image (pixel dimensions 3264 × 2448) by a factor 4
in both the horizontal and vertical directions to pixel dimensions
of 816 × 612, which has proven to provide a good balance
between the wound resolution and the processing efficiency.
In practice, we use the standard API for image resize on the