All pixel formats supported by libjpeg-turbo are supported by this wrapper. The complete list is here:

• :rgb — Decompressed image contains 3-byte pixels. Each pixel contains red, green and blue components.
• :bgr — Decompressed image contains 3-byte pixels. Each pixel contains blue, green and red components.
• :rgbx — Decompressed image contains 4-byte pixels. Each pixel contains red, green, blue components and a value X which is ignored.
• :xbgr — Decompressed image contains 4-byte pixels. Each pixel contains a value X which is ignored and blue, green and red components.
• :gray — Decompressed image contains 1-byte pixels containing grayscale component.
• :rgba — Decompressed image contains 4-byte pixels. Each pixel contains red, green, blue and alpha components.
• :bgra — Decompressed image contains 4-byte pixels. Each pixel contains blue, green, red and alpha components.
• :abgr — Decompressed image contains 4-byte pixels. Each pixel contains alpha, blue, green and red components.
• :argb — Decompressed image contains 4-byte pixels. Each pixel contains alpha, red, green and blue components.
• :cmyk — Decompressed image contains 4-byte pixels. Each pixel contains cyan, magneta, yellow and black components.