RGB24 vs. I420

[Josh Wilson]

For christmas this year, I received the Orion StarShoot Solar System Color Imager IV. SSSSIV for short. Unlike the Xbox Camera, this has two different color spaces-- RGB24 and I420. After switching back and forth several times, I couldn't see any difference in the images.

But could someone please explain the difference between them as far as which is better for imaging planetary objects?

[Guy Wells]

I want to know too...

[cgarry]

With RGB24 the red, green and blue values for a pixel are each stored as 8 bit values.  This requires 24 bits per pixel.

I420 works on the principle that the human eye has good resolution in luminance, but bad resolution in chrominance (colour).  So the luminance for each pixel is calculated and stored as 8 bits.  Then the colour is sub-sampled into 2 x 2 squares and two 8-bit colour values (actually colour difference values) are stored for each 2 x 2 square.  This requires 12 bits per pixel, hence I420 files are smaller than RGB24 files.

So basically I420 has thrown away data in order to reduce the file size.  While this may not be noticeable to the human eye I would not choose this format for my hard earned data if given the choice.

Cheers,

Chris