gerry_boughan

<p>Sorry...that's cambridgeincolour.com......incorrectly spelled coloUr the Yank way!</p>

<p>Pinched from my colleague at cambridgeincolor.com Colin Southern:<br>

"if you examine pixels from a relatively low pixel camera with ones from a much higher pixel camera - both at 100% - then you're not comparing apples with apples; you'd need to compare them so that the images (or portions thereof) were the same size which may mean that the lower resolution camera gets inspected at 100%, but the higher resolution camera at only 50% (or there abouts) - and at 50% the noise will appear less.You'll never eliminate noise; the goal is to get it to a level where it's not noticeable or detectable, and correct exposure has a LOT to do with that. Sensors on modern cameras can capture around 12 stops of dynamic range, but we generally only need around 6 or them - which is good because the top 6 are pretty clean (well above the noise floor) but if you under-expose by - say - 3 stops then you're essentailly use stops 9 down to 3 of the sensors dynamic range ... and at 3 stops up from the noise floor there'll be quite a bit of noise creeping in ... and the more you under-expose, the worse it gets. If you under-exposed by 6 stops then the remaining 6 stops that you had remaining would be marginal quality at the "highlight" end, and pure noise at the other. So the first rule is to get as far away from the noise floor as possible.<br /> <br /> But wait, there's more ...<br /> <br /> When I said that we typically only need 6 or the potentially 12 stops available I lied! (sort of) - that's pretty much the case with a normal reflective scene taken during the day (even with a little backlighting) - but at night things change; the black areas aren't light reflecting off a black object (which normally reflects quite a bit of light) ... it's pure shadow (due to the fact that this thing called the earth is between your subject and the sun) - but - you have some comparitively very bright highlights in the form of lights (eg street lights) (highlights) - and then you have areas inbetween where the light level is somewhere inbetween. All of this is typically too much for the sensor to handle - but - the camera is programed to give a fair amount of weight to protecting highlights ) - not all of them, but it'll usually set the exposure such that the highlights aren't blown too badly ... but at the expense of totally under-exposed midtones. In post-processing you decide "uh - looks too dark overall (you'll be primarily looking at wide-range midtones) so you'll do whatever it takes to raise their levels and thus raise both the under-exposed midtones and a fair amount of noise that's also lurking around those areas.<br /> <br /> So the best way to handle night time exposures (in my opinion anyway) is to simply use manual mode and simply increase the exposure so that the MIDTONES look to be an acceptable exposure on your review screen. Yes, you'll have small areas of blown highlights from the like of street lighting, but that's just the way it is ... small areas of blown highlight from lighting looks a whole lot better than large noise areas from under-exposed midtone. Bracketing your exposures is also a good idea until you get the hang of it (and even then it's often still a good idea).<br /> <br /> Many cameras are only capable of taking a 30 second shot (maximum) in manual, Tv, or Av modes ... so often you'll need to put the camera in bulb mode (and preferably use a timer, unless you're a glutton for punishment). With a timer you can set something like a 16 minute exposure and then go sit in a warm car while the camera does it's thing - however - if waiting isn't your thing you can shorten the exposure by using higher ISOs - but - they also reduce dynamic range (but long exposures can also increase noise) - so often you have to find a tradeoff ... usually if I'm standing in freezing water then high ISO / less dynamic range wins!<br /> <br /> Having just said all that ... another technique for reducing noise is to combine multiple images of the same scene / exposure to reduce noise (it gets averaged out). It works best with high ISO (eg for 1600 ISO take 16 shots) but can also be used on low ISO shots to further improve things (so long as any movement in the capture is desireable (eg clouds) -- this is where expensive tripods win over toy tripods!"</p>

<p>Ahhh...Thx. Jim. Back to the same 'ole.</p>

<p>Thx., Jeffrey. Let us know what happens. I use CS3 and wanted to wait to upgrade to 4. The DNG converter seems painfully slow so would be good if this plug-in works.</p>

<p>Recently, I took two images to my print shop: #1-Converted to jpg from psd using the Image Processor WITHOUT checking the box "Convert to sRGB profile" #2-Same but box checked. The printer confirmed that there was a distinct difference in color when viewed on his machine. Mike: I view these jpgs in PS so that isn't the issue. Patrick: Since sRGB has a lesser color range, I would think that would not be the case. Still don't get it.</p>

<p>After processing my RAW files in ACR, I save in .psd. For convenience, I use the Image Processor to convert files to jpg as needed. The RAW and .psd files are Adobe RGB 1998, however, I have to check the box in the Image Processor "Convert to sRGB profile" or they will end up a completely different hue. Why would I have to convert to sRGB from RGB if I wanted them to remain the same hue?</p>

<p>Thx. I can't figure out any reason to save them either.</p>

<p>This is slightly off-topic but I'll ask it here: Is there any reason to keep the original CR2 file after the DBG converter creates a dng? Doesn't ACR 4.6 create a xmp file after processing?</p>

<p>Is there any reason to save the original CR2 along with the converted .dng?</p>