Selective Sharpening in Photoshop (Tutorial)

[johnrt]

I am really very, very bored with the weather at the moment, I last completed an image in September! Rubbish!

When I actually do manage to produce an image, one of the most often read comments is on the level of detail and subtle areas of contrast & with just a 6"scope!!!! So, I decided to pen a little tutorial on sharpening selective areas of astro images using photoshop CS5. This is how I go about it, there's lots of ways to get the same results in Pixinsight with all manner of equations and masks, and even in Photoshop too, but I found this to be the simplest and quickest way to get a quality result.

Whenever I process an image I try to keep the Wodaski zone method in mind as much as I can, reading a couple of his books really honed my processing skills a while back, and I think he makes a lot of sense when he breaks down images during processing to dark, mid and light areas or low, mid and high signal to noise areas if you prefer.

Well I hope it's of use and can be of benefit to a few of you out there, should of course you eventually get a bit of clear sky to poke a telescope in to

http://cloudedout.squarespace.com/blog/2015/12/7/selevtive-sharpening-in-photoshop

[RikM]

Smashing tutorial John. That's exactly the way I do it as well. I sometimes use a two stage approach targeting large structures with a 30-40px radius and then tackling the fine stuff with a 5-8px radius version. Doing it this way I find much more comfortable than mathematical masking. 

[jsmoraes]

Good idea and results. I tested with one of my photos and I saw great improvement. Thank you for sharing !

[johnrt]

Thank you both very much, how excellent to have a new convert too

[Uranium235]

A very good tutorial there! Very similar to the method I use (except I do star protection during the first step), and then as you do, paint the sharpness in where needed.

However, you condensing it to an action is the cherry on the cake - splendid! I might give it whirl next time im at the PC

[johnrt]

A very good tutorial there! Very similar to the method I use (except I do star protection during the first step), and then as you do, paint the sharpness in where needed.

However, you condensing it to an action is the cherry on the cake - splendid! I might give it whirl next time im at the PC

Thank you Rob, I do exactly as you describe when processing a full image, get the stars separated out so you can happily paint away without worrying about catching them

[Tinker1947]

Very interesting tutorial, nicely put together......

[ollypenrice]

An excellent explanation. Thanks for posting.  Again I do things in a somewhat similar way but with differences which probably don't amount to much. (My global sharpening of one layer, done with stars excluded, tends to be via unsharp mask.)

However, I have a question. When we have our two layers, one sharpened and one not, we can put a mask between them and erase the mask where we want to let the sharpening through. However, we can, if we wish, dispense with the mask and erase, directly, an unsharpened top layer with a feathered eraser of any opacity we like. Why do we need the mask? Since I couldn't answer this question to my own satisfaction I stopped using the mask!

Another tool I use for zoning is the colour select tool. I find this is very good for picking up just the zones you want to pick up. I tend to use it to find areas of faint signal and hence noise. I'll then give these selections a bit of careful NR.

I do admire, greatly, the delicacy of detail in your images and will certainly try the High Pass approach. It may well be that NB and broadband sharpening need very different approaches.

Olly

[johnrt]

G'day Olly,

I see where you are coming from in your approach to the mask, I normally only want to sharpen a very small portion of my images, so the mask works well as I only need to erase a few small spots. However, I see your method of erasing the sharpened layer and dispensing with the mask where the frame is full of detail to sharpen makes much more sense, as again, you will only need to erase small amounts and leave the majority in place. Almost like a kind of galaxy v's nebula method.

I've not played with unsharp masks, I will see how they compare to the high pass.

[ollypenrice]

G'day Olly,

I see where you are coming from in your approach to the mask, I normally only want to sharpen a very small portion of my images, so the mask works well as I only need to erase a few small spots. However, I see your method of erasing the sharpened layer and dispensing with the mask where the frame is full of detail to sharpen makes much more sense, as again, you will only need to erase small amounts and leave the majority in place. Almost like a kind of galaxy v's nebula method.

I've not played with unsharp masks, I will see how they compare to the high pass.

I, too, pass very little of the sharpened image into the final one. It's edges, of course, which matter.

Olly

[RikM]

Using a mask is non-destructive, so if you change your mind, you can change the brush colour to black and paint note mask to smooth it out again. If you are brave and confident, you can of course erase the bits you don't want on the sharpened layer but I since I am neither, I work in the mask until I get it right and then flatten it at the end.

[opticalpath]

Like Rik, I prefer to use a mask for the great flexibility it provides.  It's just as easy to paint on to a mask as it is to use the eraser, but you also have the full range of PS tools to adjust or repair the mask if you need to, and to moderate or intensify its effects locally. 

Adrian

[Uranium235]

I've just compared the action to my usual workflow on an M42 I shot the other night, and it comes out pretty darn close! It should prove very handy for future sessions as I often like to stack and process on the fly (so I can see how the image is coming along).

[johnrt]

Glad it's proving useful Rob, I can't help but start stacking as soon as I've got 4/5 subs to see what's going on, I must process every images about 10 times before the final version!

[steppenwolf]

I can't help but start stacking as soon as I've got 4/5 subs to see what's going on, I must process every images about 10 times before the final version!

Me too, John!!

Excellent tutorial - very similar to my own method although I don't use the mask either, I copy the lower layer and place it above the sharp layer then use the eraser on the bits I want sharpened - just a historic thing for me that goes back to when I first started sharpening and smoothing in the same image stack!

[ollypenrice]

Using a mask is non-destructive, so if you change your mind, you can change the brush colour to black and paint note mask to smooth it out again. If you are brave and confident, you can of course erase the bits you don't want on the sharpened layer but I since I am neither, I work in the mask until I get it right and then flatten it at the end.

I don't get this. Sorry to be thick. If, not using a mask, I make an erasing gesture on a top layer over a modified layer and don't like it, I hit CtrlZ. I then try the same erasing gesture at a lower opacity. I struggle (actually I fail!) to see the difference.

Olly

[opticalpath]

If you're several steps further on before you notice a bit you wish you hadn't erased or want to fine tune, it's not such an easy process to adjust or undo just that portion if you used the eraser.  If instead you 'erase' by creating a blocking mask, then painting in the mask with a brush (in exactly the same way and in the same places as you would have used the eraser), you can go back at any later stage and use a white or black brush or other tools on the mask - locally or globally - to undo/ weaken/ soften/ expand any erasing that you change your mind about or want to experiment with.

I find it easier to put the sharpened layer on top with a full blocking (black) mask, then to paint in the mask, in white, the areas I want sharpened.  It's then very easy to go back and refine/ redo any areas of the mask to adjust the effect. 

Adrian

[ollypenrice]

If you're several steps further on before you notice a bit you wish you hadn't erased or want to fine tune, it's not such an easy process to adjust or undo just that portion if you used the eraser.  If instead you 'erase' by creating a blocking mask, then painting in the mask with a brush (in exactly the same way and in the same places as you would have used the eraser), you can go back at any later stage and use a white or black brush or other tools on the mask - locally or globally - to undo/ weaken/ soften/ expand any erasing that you change your mind about or want to experiment with.

I find it easier to put the sharpened layer on top with a full blocking (black) mask, then to paint in the mask, in white, the areas I want sharpened.  It's then very easy to go back and refine/ redo any areas of the mask to adjust the effect. 

Adrian

OK, I see this point, yes.

Olly

[Alien 13]

I never use direct actions on an image I much prefer to use masks or adjustment layres even levels is done as an adjustment layer.

Alan

[johnrt]

Well I certainly didn't foresee the use of a mask to be so controversial

[melsky]

Pretty much the way I do it John and always with a layer mask as it non destructive, if you change you mind the next day you can go back and try again. By the way instead of making a layer mask and filling it with black with the paint bucket you can just hold down the alt key when you click on the mask icon and you get a filled one straight away [emoji4]

Mel

[johnrt]

By the way instead of making a layer mask and filling it with black with the paint bucket you can just hold down the alt key when you click on the mask icon and you get a filled one straight away [emoji4]

Mel

Awesome tip! Didn't know that!

[ollypenrice]

Well I certainly didn't foresee the use of a mask to be so controversial

My fault, sorry!!! 

Olly

[gnomus]

The other advantage of using a masked, sharpened layer on top is that once you are finished with the painting of the mask and take a step back, if you feel that you have overdone the sharpening you can dial it back with the opacity slider for the masked, sharpened layer.  I use this technique often (possibly always) with my terrestrial photographs.  I move the opacity slider back to zero and eyeball the picture whilst I move the slider gradually to the right - you can see the point at which the sharpening 'kicks in' (and make a mental note of the percentage).  You can then continue on to 100% and note if there is any further improvement and see where this ends and so forth. 

Yikes - what on earth am I doing venturing an opinion amidst such lofty company?

[RikM]

I don't get this. Sorry to be thick. If, not using a mask, I make an erasing gesture on a top layer over a modified layer and don't like it, I hit CtrlZ. I then try the same erasing gesture at a lower opacity. I struggle (actually I fail!) to see the difference.

Olly

If you're several steps further on before you notice a bit you wish you hadn't erased or want to fine tune, it's not such an easy process to adjust or undo just that portion if you used the eraser. If instead you 'erase' by creating a blocking mask, then painting in the mask with a brush (in exactly the same way and in the same places as you would have used the eraser), you can go back at any later stage and use a white or black brush or other tools on the mask - locally or globally - to undo/ weaken/ soften/ expand any erasing that you change your mind about or want to experiment with.

I find it easier to put the sharpened layer on top with a full blocking (black) mask, then to paint in the mask, in white, the areas I want sharpened. It's then very easy to go back and refine/ redo any areas of the mask to adjust the effect.

Adrian

Adrian explains it perfectly. It just gives you more flexibility to adjust specific things later, rather than 'undo'ing several steps or even starting again. There's no fundamental difference.