Продолжаю статью для совместного перевода. Пишите либо в комментах, либо в личку. Я по-ходу дела буду обновлять саму статью.

image_brightness if set, corrects the brightness. value between -127 and 127 (default: null)
$handle->image_brightness = 40;

image_contrast if set, corrects the contrast. value between -127 and 127 (default: null)
$handle->image_contrast = 50;

image_tint_color if set, will tint the image with a color, value as hexadecimal #FFFFFF (default: null)
$handle->image_tint_color = '#FF0000';

image_overlay_color if set, will add a colored overlay, value as hexadecimal #FFFFFF (default: null)
$handle->image_overlay_color = '#FF0000';

image_overlay_percent used when image_overlay_color is set, determines the opacity (default: 50)
$handle->image_overlay_percent = 20;

image_negative inverts the colors in the image (default: false)
$handle->image_negative = true;

image_greyscale transforms an image into greyscale (default: false)
$handle->image_greyscale = true;

image_threshold applies a threshold filter. value between -127 and 127 (default: null)
$handle->image_threshold = 20;

image_text creates a text label on the image, value is a string, with eventual replacement tokens (default: null)
$handle->image_text = 'test';

image_text_direction text label direction, either 'h' horizontal or 'v' vertical (default: 'h')
$handle->image_text_direction = 'v';

image_text_color text color for the text label, in hexadecimal (default: #FFFFFF)
$handle->image_text_color = '#FF0000';

image_text_percent text opacity on the text label, integer between 0 and 100 (default: 100)
$handle->image_text_percent = 50;

image_text_background text label background color, in hexadecimal (default: null)
$handle->image_text_background = '#FFFFFF';

image_text_background_percent text label background opacity, integer between 0 and 100 (default: 100)
$handle->image_text_background_percent = 50;

image_text_font built-in font for the text label, from 1 to 5. 1 is the smallest (default: 5)
$handle->image_text_font = 4;

image_text_x absolute text label position, in pixels from the left border. can be negative (default: null)
$handle->image_text_x = 5;

image_text_y absolute text label position, in pixels from the top border. can be negative (default: null)
$handle->image_text_y = 5;

image_text_position text label position withing the image, a combination of one or two from 'TBLR': top, bottom, left, right (default: null)
$handle->image_text_position = 'LR';

image_text_padding text label padding, in pixels. can be overridden by image_text_padding_x and image_text_padding_y (default: 0)
$handle->image_text_padding = 5;

image_text_padding_x text label horizontal padding (default: null)
$handle->image_text_padding_x = 2;

image_text_padding_y text label vertical padding (default: null)
$handle->image_text_padding_y = 10;

image_text_alignment text alignment when text has multiple lines, either 'L', 'C' or 'R' (default: 'C')
$handle->image_text_alignment = 'R';

image_text_line_spacing space between lines in pixels, when text has multiple lines (default: 0)
$handle->image_text_line_spacing = 3;

image_flip flips image, wither 'h' horizontal or 'v' vertical (default: null)
$handle->image_flip = 'h';

image_rotate rotates image. possible values are 90, 180 and 270 (default: null)
$handle->image_rotate = 90;

image_crop crops image. accepts 4, 2 or 1 values as 'T R B L' or 'TB LR' or 'TBLR'. dimension can be 20, or 20px or 20% (default: null)
$handle->image_crop = array(50,40,30,20); OR '-20 20%'…

image_precrop crops image, before an eventual resizing. accepts 4, 2 or 1 values as 'T R B L' or 'TB LR' or 'TBLR'. dimension can be 20, or 20px or 20% (default: null)
$handle->image_precrop = array(50,40,30,20); OR '-20 20%'…

image_bevel adds a bevel border to the image. value is thickness in pixels (default: null)
$handle->image_bevel = 20;

image_bevel_color1 top and left bevel color, in hexadecimal (default: #FFFFFF)
$handle->image_bevel_color1 = '#FFFFFF';

image_bevel_color2 bottom and right bevel color, in hexadecimal (default: #000000)
$handle->image_bevel_color2 = '#000000';

image_border adds a unicolor border to the image. accepts 4, 2 or 1 values as 'T R B L' or 'TB LR' or 'TBLR'. dimension can be 20, or 20px or 20% (default: null)
$handle->image_border = '3px'; OR '-20 20%' OR array(3,2)…

image_border_color border color, in hexadecimal (default: #FFFFFF)
$handle->image_border_color = '#FFFFFF';

image_frame type of frame: 1=flat 2=crossed (default: null)
$handle->image_frame = 2;

image_frame_colors list of hex colors, in an array or a space separated string (default: '#FFFFFF #999999 #666666 #000000')
$handle->image_frame_colors = array('#999999', '#FF0000', '#666666', '#333333', '#000000');

image_watermark adds a watermark on the image, value is a local filename. accepted files are GIF, JPG, BMP, PNG and PNG alpha (default: null)
$handle->image_watermark = 'watermark.png';

image_watermark_x absolute watermark position, in pixels from the left border. can be negative (default: null)
$handle->image_watermark_x = 5;

image_watermark_y absolute watermark position, in pixels from the top border. can be negative (default: null)
$handle->image_watermark_y = 5;

image_watermark_position watermark position withing the image, a combination of one or two from 'TBLR': top, bottom, left, right (default: null)
$handle->image_watermark_position = 'LR';

image_reflection_height if set, a reflection will be added. Format is either in pixels or percentage, such as 40, '40', '40px' or '40%' (default: null)
$handle->image_reflection_height = '25%';

image_reflection_space space in pixels between the source image and the reflection, can be negative (default: null)
$handle->image_reflection_space = 3;

image_reflection_color reflection background color, in hexadecimal. Now deprecated in favor of image_default_color (default: #FFFFFF)
$handle->image_default_color = '#000000';

image_reflection_opacity opacity level at which the reflection starts, integer between 0 and 100 (default: 60)
$handle->image_reflection_opacity = 60;