beginners start here for those who've bought a digital camera, and need to use it
Posted 23 June 2012 - 12:41 PM
For some time, I've known of Jim McCordall's web site, full of simple explanations and practical hints wrt photography, it is well worth exploring. For example, the following http://www.mccordall...for-retouching/ shows the effect of 16/8 bit image editing 'without confusing the enemy'.
Also, there are various amusing stories about shoots in his earlier career.
Having recommended Sagelight to a friend of mine, who knows little about photography, I'm wondering how he will manage.
Posted 23 June 2012 - 07:35 PM
"An 8 bit pixel has greater pixel depth or bit depth . . . "
"A colour image in this category will have 8 bits on each of the red, green and blue channels.
The total pixel content of the image combine to make the file size. An 8 bit pixel uses one 'byte' of computer memory and a thousand bytes amount to one 'megabyte' of memory."
An image with 8 bits on each channel is a 24bit color image. Pixel count in an image relates to file size according to the mapping of colors to bits, and it's not as simple as the author makes out. And, for crying out loud, 1000 bytes is 24 less than a "KILOBYTE", NOT a megabyte.
"The greater the bit depth or pixel depth in this 'rod' of digital information, the greater will be the number of colours and information stored. Therefore, the digital image will give a more accurate representation of the original."
"Rod"? Way to use standard terminology! And does he mean "bit depth" or "pixel depth"? Whatever he might mean by "pixel depth", it can't be the same thing.
"Many scanners can scan film in 16 bit per channel mode and this will capture considerably more information and hence more colours, tones and details. In actual fact, Photoshop works in 15 bit + 1 unit, which amounts to 215. This produces 32,769 values, which is still considerably more than in standard 8 bit mode."
By this point, I was about ready to scream. "Scanners"? So what? "15 bit + 1 unit"? What does that even mean? It's only after thinking about it for a while that I realized he meant that he thinks that means the same thing as 2^15, or 2 to the 15th power, but either way 2^15 is not 32769, and neither is 2^16, which is what he should have said. Depending on what exactly he's trying to get across which is not at all certain. FYI, 2^15 is 32768, and PS works in 16 bits (or other bit depths), not whatever he's trying to say there. He MIGHT have been trying to convey that camera sensors don't actually output a full 16 bit range of values, but those (actually closer to) ~14 bits cannot be stuffed into less than 2 bytes.
However much that guy might be a great photographer, people who cannot discuss binary values, bits, and bytes any more accurately than that should not be presuming to teach people digital photography.
Posted 24 June 2012 - 12:15 AM
Basic Idea: It does explain the idea, and is the one that stuck to me for life. Ignoring the fact that its in PS, it explains the stuff. Basically with 8bit of color for red Green and blue (RGB), you only have 256 shades of red, green, blue. But mix the colors, 256r * 256g * 256b give you 16,777,216 million colors. Yeah thats a lot but its not like we live in a techni color world where everyone looks like a tie die t-shirt.. Realisticly most things in our world are solid color with very limited mixed values so your still really only limited to storing 256 shades of what ever color you may have spanning things in your image. in 16bit color this range is pretty insane but its needed to avoid imperfection & artifacts that may result from editing photos in 8bit color. A lot of Sagelight works in 16bit+16bit+16bit per value or 48bit total, and in fact a lot of Sagelight goes beyond this to 32bit, 64bit, and with the resize function 192bit values.
8bit vs 16bit
Posted 25 June 2012 - 03:16 AM
In 16-bit mode, Adobe is basically 15-bits and not 16. It uses 0-1.0 basis for the 16-bit values, where 0x8000 is 1.0. Therefore, all other values are from 0-0x7ffff (32767) in a 15-bit field. Sagelight (and, I presume, many other 16-bit editors) use the entire range of 0-0xFFFF (i.e. 0-65535), but still calculates values as 0-1.0.