PNG Options and Extensions

• Background Color (bKGD)
• Timestamp (tIME)
• Latin-1 Text Annotations (tEXt, zTXt)
• International Text Annotations (iTXt)
• Histogram (hIST)
• Suggested Palette (sPLT)
• Significant Bits (sBIT)
• Physical Pixel Dimensions (pHYs)
• Physical Scale (sCAL)
• Image Offset (oFFs)
• Pixel Calibration (pCAL)
• Fractal Parameters (fRAc)
• GIF Conversion Info (gIFg, gIFx)
• GIF Plain Text (gIFt)
• Other Chunks

In addition to the core chunk types described thus far, the Portable Network Graphics format supports a whole host of optional chunks for various purposes, from text annotations to conversion information. These are described in the following sections, very roughly in order of importance to the average user.