On Mon, Apr 5, 2010 at 10:27 AM, Jack Davis <[email protected]> wrote: > I'll offer mine the nebulous term by saying that if at least some surface > areas are rendered featureless by virtue of being too bright, I'd consider > those areas "blown out." Many images can tolerate a certain amount of this > condition, but it's amount is the criteria and varies with each viewer. Said > areas must, of course, contain some available mask detail which defines the > surface. > IOW, I'm not talking about an absolute ball of glare wherein no detail is > discernible.
There's nothing nebulous about "blown out". Consider areas of pure white with no detail as Zone 9 on the Zone System scale defined as follows: Zone 0 – key black or pure black – carbon or photo paper black. Zone 1 – near black – shadows in faint light or rooms without light. Zone 2 – dark gray/black – only subtle textures are visible. Zone 3 – very dark gray – distinct shadow texture is visible. Zone 4 – medium dark gray – slightly darker “black” skin, dark foliage or shadows in landscapes. Zone 5 – medium gray or 18% gray – darker “white” skin or lighter “black skin,” light foliage or the dark blue of a clear blue sky. Zone 6 – mid-tone gray – average “white” skin or shaded areas in snow on a bright, sunlit day. Zone 7 – light gray – pale “white” skin, a concrete walkway in sunlight. Zone 8 – gray/white, near white – distinct highlight detail, like a white wall in sunlight or brilliant surfaces in flat light. Zone 9 – known as key white or pure white – pure white paper or snow in bright sunlight. (Normally I think of the Zones as being from 1-10, but Ansel was a C programmer and did a 0-based count ... ;-) So, by definition, anything you want detail in is "blown out" if your exposure has placed it above Zone 8 on the above scale. Since I've never seen any application use 16-bit number scales to describe pixel values, you can determine what areas of your image are "blown out" in Photoshop or Lightroom using either a percentage scale or an 8-bit pixel value scale and floating the cursor over white-looking areas while looking at the information display panel. Presuming that the exposure did not go to saturation and there is data in those bright areas, you can place them in adjustment using the Exposure (aka white point) sliders. This table makes it easy ... http://homepage.mac.com/godders/zone-system-numbers.jpg EG: you have a near blown out area in a photo that you want to ensure images with detail on screen and in your prints. Float the cursor over it in Lightroom and see that it is currently at about 94% in all channels (or in one of them if that is the significant color of the area). Nudge the Exposure slider in the negative direction until it is in the range of about 85-88% to set that as the brightest point. Now make adjustments with the mid-tone, black point and Tone Panel to bring the rest of the photo into line with a satisfactory display. A certain amount of area at Zone 9 is fine, as long as it's not where you wanted to convey detail. Too much Zone 9 in an image generally looks bad. Another thing to be aware of is that many papers and monitor screens cannot display the full 10 zone scale very well, or have non-linear characteristics ... That's why calibration, profiling and testing for DR are essential to good quality image display, whether on screen or on paper. -- Godfrey godfreydigiorgi.posterous.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
