The edge finding method of sharpening

I will have to find time to put everything I have managed to work out about sharpening for digital photography down. But for the moment here is the best fix I have discovered for providing defined edges (sharpness) to a digital image.

Normal an unsharp mask (USM) is fine, but occasionally I need to boost certain areas selectively or there is a degree of noise which gets sharpened destroying the image quality. For these situations I use a filter which used to be called find edges but is actually a high pass filter.

step 1 duplicate your image
step 2 run a High pass filter or equivalent on the duplicate. You should end up with a grey image with the edges defined. Using an option you should be able to define how many pixels this is. Don't go more than 3 if you can help it as higher than this and the prints look odd.
step 3 change the blend mode to either overlay or soft overlay. You can use a hard overlay but I tend to find it looks a bit unreal and sometimes over grainy.
step 4 adjust the opacity to suit your needs
step 5 delete the unwanted areas of sharpness from the duplicate high pass. So for example in a portrait eyes need to be sharp but the outline of the head and body can remain soft. So I would run the eraser over all but the eyes and nose. You can also use this remove noise from the image.

A final note - sharpening is not an excuse for poor focussing. BUT you can rescue the odd image using this method when you didn't quite get it right, PROVIDING you don't intead to make a large print.

Ortonisation of digital images

I won't go into the details of the Orton effect - except to say it produces a light, colour saturated, image with soft details akin to an impressionist painting. For more detailed description see Wikipedia or this blog for working with JPEGS.

My method starts with the raw file - which allows you to go back to the original exposure method a produce a sandwich of two "slides". Prepare two exposures at one and two stops above your average (neutral) exposure point. Save these in your preferred format, I use TIFF because of the information lost in compression makes large prints difficult.

Sharpen the "slide" overexposed by 2 stops, and add Gaussian blur (the amount depends on the final effect you want) to the "slide" overexposed by one stop. This second slide has now become the poor man's equivalent of the out of focus slide. Although technically not the same and perhaps not benefiting from bokeh caused by the lens arrangement, for most purposes the result is the same and better than a 3 layer sandwich used for JPEGS.

Now comes the time to combine our two slides and create an image with the softness and colour of an Ortonised image. With physical slides the out of focus slide would be used to screen the in focus slide. So stack your blurred "slide" over the focussed one and select the screen blending mode. You now have your final image which should provide an impressionistic style, which you may want to tweak by adjusting the degree of screening, and the final levels. The beauty of using digital is of course if you feel the image is too overexposed for your tastes you can then go back and repeat the process at lower exposures. Try doing that with a slide film back in the darkroom.

Contrast masking

When the contrast in a photograph is just a little too defined you want to lighten the shadows and darken the highlights. You can work on this with the levels, but the image may not contain enough information to work with. Your histogram is pretty much at its limits and/or is very complex so masking and working on certain areas are not practical. If you shoot in RAW there is plenty of scope to recover some of these details. Creating a high dynamic range photograph being the ultimate solution. But consider a contrast mask, which is quicker and gives a very different look. It has similar characteristics to the muslin style effect from the last post. It uses Gaussian blur to add or subtract light from the image.

Start with your flattened b/w image and duplicate this as a new layer with whatever software you use. The invert the image, ie make it a negative.

Now change the blending mode to Overlayer - this will bring up the shadows and reduce the highlights, but it also flattens the image. This is pretty much what you would do with a low contrast paper so no change there then. The plus side is it does sharpen the image - you are getting effectively an unsharp mask (USM)

Next, is the applying the changes to just the light by softening the edges. We do this by applying somewhere between 10 and 60 pixels worth of Gaussian blur to the negative image. Halos can form so it may be necessary to dial back the blur to avoid this.





The resultant image should now have less contrast and have lifted some of the detail and made the highlights less harsh.

Muslin effect

Prepare the image as you would normally, adjusting your levels and Hue/saturation (other filters) to give a well balanced shot.
Duplicate background layer (keep adjacent to background) and add 30 pixels of Gaussian blur. This seems excessive, but ultimately it is the light level radius from a point we are looking for. The greater the blur the greater the appearance of a glow there will be. Now change the blending to lighten. Adjust the opacity to give the desired level of softness and glow. If the softness is now high enough then you will need to increase the Gaussian blur in the duplicated layer (ie start again).

The diffuse glow and a blur can create a similar effect, but is less controllable and requires more fiddling around, and often does not provide the soft glow I am looking for.