2. parse_csv_to_json.php - converts SNG csv into JSON
input: SNG-metadata.csv
output: SNG-metadata.json - JSON formated data
3a. download_thumbs.php - this should be executed just once, downloads thumbnails from SNG and saves filtered JSON
input: SNG-metadata.json
output: SNG-metadata-with-thumbs.json - filtered data containing just those which have thumbnail avialable, and thumbnail files stored in folder "thumbs"
3b. downloader.php - re-download, using filtered JSON (if we want to download different size of thumbnails)
input: SNG-metadata-with-thumbs.json
output: redownloaded thumbnails
4. generate_histogram.php - processes saved thumbnails retrieving histagram from them
input: SNG-metadata-with-thumbs.json, thumbnail images in folder thumbs
output: JSON files in histogram folder, naming convention is same as naming convention with images. Each file contains luma, red, green, blue histogram
histogram array contains luma, red, green, blue histagram data for each artwork. indices/keys are color values - 32rd element in [histagram][red] contains percentage of red color with value 32 in image. So [histagram][red][32]=3.59 means that 3.59% of all pixels in image contains red color with value 32.