Examine the low-level internals of PNG image files. Chunks supported: - IHDR - Image's 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 - Apple's proprietary extension to PNG. - bKGD - Default background color to present the image against. - tIME - Last-modification time.