This first example is an indexed color (palette) image. It is interlaced, so suitable software can give a progressive display.
Technical details of this image, as reported by pngcheck 1.95:
File: nurbcup2si.png chunk IHDR at offset 0x0000c, length 13 350 x 208 image, 8-bit colormap, interlaced chunk gAMA at offset 0x00025, length 4: 0.44843 chunk PLTE at offset 0x00035, length 711: 237 palette entries chunk tEXt at offset 0x00308, length 56, keyword: Software chunk IDAT at offset 0x0034c, length 8192 chunk IDAT at offset 0x02358, length 8192 chunk IDAT at offset 0x04364, length 8192 chunk IDAT at offset 0x06370, length 8192 chunk IDAT at offset 0x0837c, length 575 chunk tIME at offset 0x085c7, length 7: 14 Aug 1996 12:23:35 GMT chunk IEND at offset 0x085da, length 0 No errors detected in nurbcup2si.png.
The second example is a large truecolor image generated by a raytracer, and is a visualisation of a 6 by 6 by 6 color cube in CIE LUV color space.
Technical details of this image, as reported by pngcheck 1.95:
File: 666.png
chunk IHDR at offset 0x0000c, length 13
800 x 400 image, 24-bit RGB, interlaced
chunk gAMA at offset 0x00025, length 4: 0.45000
chunk cHRM at offset 0x00035, length 32
White x = 0.283 y = 0.298, Red x = 0.625 y = 0.34
Green x = 0.285 y = 0.605, Blue x = 0.15 y = 0.065
chunk tEXt at offset 0x00061, length 56, keyword: Software
chunk tEXt at offset 0x000a5, length 89, keyword: Comment
chunk IDAT at offset 0x0010a, length 8192
chunk IDAT at offset 0x02116, length 8192
chunk IDAT at offset 0x04122, length 8192
chunk IDAT at offset 0x0612e, length 8192
chunk IDAT at offset 0x0813a, length 8192
chunk IDAT at offset 0x0a146, length 8192
chunk IDAT at offset 0x0c152, length 8192
chunk IDAT at offset 0x0e15e, length 8192
chunk IDAT at offset 0x1016a, length 8192
chunk IDAT at offset 0x12176, length 8192
chunk IDAT at offset 0x14182, length 3539
chunk IEND at offset 0x14f61, length 0
No errors detected in 666.png.