Behind the pixels

ZSOLT OCSKAI - DENNIS GABOR COLLEGE

21-04-2015

A few common things about raster images

Their data are stored in pixels

The pixels contain channels

Each channel contains 8 or 16 bits of information

The number of channels is determined by the used colour space: RGB – RED GREEN BLUE

CMYK – CYAN MAGENTA YELLOW BLACK

Palette – Indexed stored Colours (GIF)

Etc…

A few common things about the raster images

Photo by Rita Szabó

R: 90

G: 84

B: 90

Shannon entropy for digital images

If we assume pixels are independent from each other, then we fit to use Claude E. Shannon’s entropy formula to process a digital image.

Where

possible range of values for the Entropy:

Where

Shannon entropy for digital images

Photo by Rita Szabó Photo by Péter Vas

Images properties:

JPG

24 bits/pixels

RGB

HEIGHT

WIDTH

ENTROPY

1000 960

667 643

12,453 15,0286

Differences between the image formats

FORMAT

ENTROPY

JPG TIFF

24 bits/pix.

48 bits/pix.

14,8282 24,7204

Images properties:

RGB

HEIGHT

10000

WIDTH

10000

TAGGED IMAGE FILE FORMAT

The TIFF is capable of:

Carrying multiple images

Storing 1, 2, 3, 4, etc channels/pixel

Storing 1, 2, 3, 4, etc… bits/channel

Multiple options to order the channels, bytes and bits

Storing Layers

For 4 GB physical storage boundary

TIFF – amount of channels for 1 pixel

RGBRGBAmultispectral

hyperspectral

Capable of carrying more than 359 channels

The 2 main byte - channel orders for 3 pixels in 1 row

I II IIIInterleaved

Per Channel

I I III

II

II

III

III

III

TIFF - head

The TIFF is owned by the Adobe Inc. and it’s just partly opened format.

The navigation map for the data structure can be found in the TAGs.

All TAGs have unique address

Some TAGs are forbidden to use / write without Adobe’s approval

There are several un-official TIFF formats

GEOTIFF

BIGTIFF

The entropy compute software for TIFF images

For the properly TIFF data reading we used the LibTIFF open source libraries

The libraries are available for C++ and .NET environments too and mostly work in the same way

We created several applications for more efficient work

The programs are available for x64 systems:

- Windows- Linux- OS X

With the programs we can:- determine the entropy for the whole

image- determine the entropy for a single

channel

Images can be:- 8, 16 bits/channels- 1, 2, 3, 4, etc. Channels/pixel

The software I

Visual Basic.NETConsole and GUI

For .NET framework with LibTiff.NET

C++ console and Java GUIFor Windows, Linux and OS X enviroments with

LibTiff

The software II

For JPG, PNG and BMP images

C# for .NET 4.0 framework

Variants for x86 and x64 systems

For educational purpose

Some unusable results

White.tiffNumber of

pixels: 1000000

Number of unique colours: 1Entropy value: 0

Black.tiffNumber of

pixels: 1000000

Number of unique colours: 1Entropy value : 0

Test_8bit_grey.tiff

Number of pixels: 2560000

Number of unique colours:

256Entropy value :

8

Test_24bit_rgb.tiff

Number of pixels: 2560000

Number of unique colours:

256Entropy value :

8

Where it has been used

The research project

Educational Applications of Entropy and Fractal Structure Analysis in Impact Assessment of Environmental Pollutions (Journal of Applied Multimedia 2./VIII./2013)

It was an agricultural project to analyse the possibilites of the pollution detections on images.

The entropy showed no significant results

The SFD (Spectral Fractal Dimension) was capable of detecting the different pollutions in the images

Important links

„Digitális Fotósuli” - GDF Workshop

SFD Information Technology Ltd. - Digital Image processing web page

Adobe Systems Inc. - Offical TIFF web page

LibTiff project - TIFF handler packages for C++ (remotesensing.org)

LibTiff.NET project - TIFF handler packages for .NET Framework (Bit Miracle)

Research project – researchgate.net