SLAMorris Final Thesis After Corrections.pdf - Cranfield University

Start of IHDR Chunk
The IHDR contains information on the format of the visual thumbnail, including
the size in pixels. This information is generally standardised for each thumbnail
cache generation algorithm. For analysts the width and height of the image can
be used to validate the visual thumbnail stored in the sub-record. The
characteristics of the PNG image such as: bit depth, colour type, compression
method, filter method and interlace method are standard PNG fields which hold
information about how the visual image is processed and stored within the file.
This information may assist with identifying characteristics of visual thumbnails
generated with different algorithms.
00 00 00 0D49 48 44 52 ‰PNG IHDR
00 00 00 0D – number of bytes in the chunks data field – 13
49 48 44 52 – Type of the chunk – IHDR – Image header
00000010 00 00 00 8000 00 00 6708020000 0047 1D DD € g G Ý
00 00 00 80 – Width of image in pixels – 128
00 00 00 67 – Height of image in pixels – 103
08 – Bit Depth – 8
02 – Colour type – True colour (Each pixel is an RGB triple)
00 – Compression Method used to compress the PNG image data
00 – Filter Method (pre-processing applied to image before compression)
00 – Interlace Method
00000020 A6
47 1D DD A6 – CRC Value for Chunk
End of IHDR Chunk
Start of sBIT Chunk
The SBIT Chunk shows the bit depth, throughout this research, only values of
‘08’ for each colour were recorded. This is another standard PNG chunk and
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