Aha! Gamma rears it's head again. This all starts with the characteristics of CRT tubes. A CRT tube does not have a linear transfer function, if you double the input voltage the light on the screen does not double. The function of the curve traditionally uses the greek letter gamma, so this function has come to be called a "gamma function".
This all came to light (pun intended) in the early days of TV, the sensors used in the TV cameras were linear, the output voltage varied directly with the light intensity, but the CRT tubes used for display were NOT linear, so the images didn't look right. They fixed this by adding a "gamma correction" circuit in the TV camera that applied the inverse of the gamma function. Most people, even technical people in the industry had no clue about this gamma issue because the cameras corrected for it, no matter where you hooked up a CRT tube in the chain to look at the picture, it looked right. Fast forward 50 years to the start of computers being used for taking and displaying images, computers are still using CRT tubes to display things, but the early crop of scanners are linear devices, just like the sensors in the TV cameras, so an image scanned on one of these and displayed on a CRT tube, didn't look right. The professionals understood this and used software to apply the gamma correction so things looked right on the screen. But when amateurs came along they didn't have any clue about this and kept on getting images that didn't look right. It didn't take too long for the market to realize the problem, all the manufacturers started shipping scanners, and then digital cameras, with the gamma correction built in, so all the image files that came out of these devices were pre gamma corrected to display well on CRTs. For quite a while this worked well. Then LCD screens came along, unfortunately LCD screens are linear devices so now all these pre-gamma corrected images don't look right any more! The makers of LCD computer monitors realized this and added the gamma function in the monitor electronics before sending the data to the LCD pannel. So these days we have the sources taking the linear data from their sensors correcting for display on a CRT, the monitor then anti-corrects back to linear space for display on the LCD. So the task here is to find out whether the Touch already does the anti-gamma correction or not. And then find out whether you scanner applies the gamma correction or not. It seems like we have a mismatch here. To test the Touch, take an image that has a wide range of different shades from light to dark that displays well on your regular computer screen and use that as cover art for an album and see how it looks on the Touch. ( it can be something you take with a digital camera or something from the web, don't use the scanner at this point). If the Touch is doing the anti-gamma correction it should look fairly decent on the Touch screen. If the Touch is not doing the correction it will look light and washed out. Now try using your scanner on a real photograph, it should look good on your computer screen. Do NOT scan cover art, a magazine page or something printed on a computer printer. If it does look good the scanner is applying gamma correction. Then try using THIS image as cover art, Does it look good on the Touch? If its light and washed out, that means the Touch is not anti-correcting. If this looks good but scanned cover art does not look good we have a different issue. If it looks DARK and contrasty then the anti-correction is too much. If it's dark and washed out then there is something weird going on! Do the tests and report on the results and we can see what needs to be done. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=95637 _______________________________________________ Touch mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/touch
