BTW, noise is relatively easy to control if you think about how things work.
Every camera has noise at every ISO. You just don't notice it at low ISOs. If you were to shoot an exposure with the lens covered, you'd get a black photo (no suprise). But if you actually moused over each individual pixel, you'd find the pixels don't technically read "0, 0, 0" for RGB ... they'd read some very low non-zero values. This is the bias value of the sensor. You'd also notice that the value varies from pixel to pixel by a very tiny amount.
When you boost ISO, the camera has to amplify the values. This means pixels that were so close (but not identical) that you could not notice a difference, start to show more of a difference and ... now you "notice" the noise.
To de-noise, the software compares pixels to it's neighbors and averages down the values and this makes the nosie go away. But a side-effect of this is that areas that are supposed to show sharp detail now start to look a little soft (becuase crisp sharp edges were "averaged" with their neighbors.)
Noise is very noticeable in flat areas that lack important detail. This means you can REALLY help an image if you could protect the areas that need to be sharp (edges of contrast) and just de-noise the areas away from the edges.
In Photoshop you can create an "edge mask" (there's no specific tool with this name ... but there are techniques to build one fairly quickly) and then de-noise the image with the edge-mask protecting the edges.
But it turns out this is a built-in feature if you use Lightroom.
Pull up your photo, switch to the Develop module, then scroll down along the right to find the "Detail" panel (that's the panel that lets you do sharpening and de-noising).
In the "Sharpening" section of the Detail box, you'll find a slider named "Masking".
Here's the trick. Instead of adjusting the slider ... HOLD DOWN your Alt/Option key WHILE moving the slider.
When the slider is all the way left and you're holding down the Alt/Option key, the whole image will go solid white. What this means is EVERYTHING is "in bounds" when it comes to adjustments for sharpening or de-noising).
As you drag the slider to the right, more and more of the image will start to go black and what you'll notice is that just edges of contrast (where you should have detail) are still white. This is your "edge mask".
When you apply sharpening, it will ONLY sharpen in areas that are white (edges of contrast) and it will NOT attempt to sharpen the black areas (flatter areas of the image that don't have contrasty detail). This means you can sharpen just the parts of the image that matter without driving up noise globally across the entire image.
ALSO... when you apply "noise reduction", it will de-noise the flat areas that lack contrasty detail but will PROTECT the edges that need contrasty detail.
There are other 3rd party tools that also apply clever techniquest (noise tends to be more noticeble in dark areas and less noticeable in highlights ... so they apply more or less aggressive de-noising depening on the tonal range of the area in the image.
Lastly... you can always grab the "adjustment brush" tool in Lightroom and tell it to just apply sharpeing or de-noising in specific areas.
I used to hate noise ... but now that I've learned technqiues for dealing with it ... it's really no big deal.
Tim Campbell
5D III, 5D IV, 60Da
