               ## Graininess Detection

 (I) What is graininess? • Graininess corresponds to high frequency content in the picture

 (II) How do we measure graininess? • If we low pass filter an image, then the graininess in the picture will become blurry Monet Monet after filtering Rembrandt Rembrandt after filtering

 (III) How exactly do we low pass filter? • Apply a Wiener filter, which is designed to filter out constant power additive noise (MATLAB help   documentation). • The Wiener filter adaptively filters using statistics estimated from a local neighborhood of each pixel (MATLAB help documentation). • The size of the neighborhood is set to be one-tenth of the size of the original picture.

 (IV) How do we measure blurriness? • Blurriness corresponds to the amount of contrast in the picture. High Contrast Low Contrast

 (V) How do we measure contrast? • Convert the image to gray scale in MATLAB. • The image is then a matrix of values from zero to one where each value corresponds to the darkness of a pixel.

 Example: Image of size 3x4 pixels • Approximate the contrast by finding the sum of the differences between elements of a row and the sum of the differences of elements of a column.

 Row contrast of example = 3.4 Column contrast of example = 2.7 • Add two sums for total contrast.

Total contrast of Example= Row contrast + Column Contrast = 6.1

 (VI) How do we compare the graininess of different pictures of different sizes? • Measure the percent change in contrast to determine the blurriness.

(Contrast of Original – Contrast of Blurred)/ Contrast of Original

 (VII) Summary of Algorithm to Measure Graininess (VIII) Graininess Trends Found Among Three Artists

 Graininess Trends: Approximated by Measuring Blurriness After Wiener Low Pass Filter • Monet paintings found in percentage range of 76 to 92. • Rembrandt paintings have no definite trend. • Picasso paintings found in percentage range of 67 to 85. • Results interesting but not useful for classification since ranges of artist overlap. Graininess Analysis MATLAB code  