Examine the low-level internals of PNG image files.
Chunks supported:
- IHDR - Images width, height and bit depth.
- PLTE - Palette.
- gAMA - Gamma.
- tEXt - Textual data.
- pHYs - Physical pixel dimensions.
- cHRM - Primary chromaticities.
- sRGB - Standard RGB color space.
- sBIT - Significants Bits.
- CgBI - Apples proprietary extension to PNG.
- bKGD - Default background color to present the image against.
- tIME - Last-modification time.
