Sharpening and Noise Reduction Sequence

[FrankMi]

I am experimenting with the Photoshop Filter/Blur/Surface Blur for noise reduction. Is there a recommended sequence for when both sharpening and noise reduction post processing need to be done?

[tclune]

I always reduce noise before sharpening -- all you'll do is enhance the noise if you sharpen before removing the noise.

[FrankMi]

Ah! Makes sense. Does that include Capture Sharpening, do the Noise Reduction, then the capture sharpening? Thank you, Tom!

[tclune]

I'm not sure I know what "capture sharpening" means. I normally only sharpen once, and it is the last thing I do. I know that a lot of people seem to sharpen for each size they wish to display, and differently for printer output or screen output. Such people are just more sophisticated than I am.

I examine the photo I am sharpening at 100% magnification and sharpen as much as does not introduce artifacts that I can see anywhere on the photo. If I do that, I am normally quite content with the look of the photo whether it is displayed on the screen or printed at any size I ever use.

The CiC tutorial shows different sharpening for printing vs screen display, and I am confident that they are more knowledgeable than I am. I just haven't found it to be necessary. And I haven't had any problem with Moire patterns when I down-res. That is probably because the folks who wrote the program that I use have built in a smart algorithm for avoiding that. But, for whatever reason, I am quite content to sharpen once and then leave the photo alone, even through resizing or outputting to differing media. FWIW

[ETA: I used to use unsharp masking for my sharpening, and was never really satisfied with the results. That is a really touchy way of sharpening, and basically just low-passes the image while accentuating the edges. I switched to Focus Magic a while back, and have been very happy with it ever since. I think it does its sharpening in Fourier space. If I had to guess, I would imagine that it is doing basically a Weiner filter, which is a two-stage filter that passes different amounts of the high frequency data and the low-frequency data, setting the transition between the two rolloffs based on an analysis of the image noise. That may be wrong, but it looks like that sort of processing to my eye. And that would explain why I normally have to cut back on the sharpening that the program recommends -- I apply noise reduction before using the Focus Magic plugin, so it presumably misconstrues the quality of the image due to the noise reduction.]

[Dave Humphries]

I am experimenting with the Photoshop Filter/Blur/Surface Blur for noise reduction. Is there a recommended sequence for when both sharpening and noise reduction post processing need to be done?

Hi Frank,

Blur has to be a really crude way to reduce noise, because unless selectively applied, it will kill fine detail (i.e. sharpness) too.

A third party method, like Neat Image is a much more effective way. It will blitz the noise without doing anywhere near so much damage to the sharpness.

Yes, I do it, when necessary, even before capture sharpening - I do both in Elements (or CS5), just after RAW conversion.

Cheers,

[Colin Southern]

Hi Frank,

The "short answer" is "yes", apply noise reduction before sharpening, so as to avoid sharpening the noise. Unfortunately, the "long answer" isn't quite that cut and dried ...

In essence, noise reduction and sharpening are - to a very significant degree - "mutually exclusive" in the real world; sharpening increases the contrast around edges whereas noise reduction "averages" areas of a photo so that the impact of the (psudo-random) noise is reduced. It all sounds nicely "compartmentalised" in theory, but in practice, noise reduction ALWAYS ends up softening an image (so more sharpening is usually required to offset that softening). So in a very real way, in just the same vein as "sharpening will also sharpen noise" (and thus making it more visibly obvious), "noise reduction will also significantly reduce the effect of a given sharpening workflow", and thus make that more visibly obvious too.

So the question really becomes "which degrades an image more; sharpened noise or a soft image"? In real-world terms, the "A" answer is "avoid creating noise in the first place" - and in my opinion, that's very easy to do - AT ANY ISO. Simply follow 2 rules:

(1) Avoid under-exposure (especially at high ISOs because the dynamic range of the capture decreases with increasing ISO, so the "safety margin" of a high-iso capture is significantly reduced to start with, resulting in more noise being made visible when the levels of the image are adjusted in post-processing - or in other words, if the image is exposed correctly in the first place - no raising of levels will be required - and the information captured will be as far away from the noise floor as possible.

(2) Avoid excessively cropping an image. Noise is very small - far too small for our eyes to resolve at normal image sizes. Put another way; "if you don't crop an image excessively, the ONLY time you'll be able to see the noise in a correctly-exposed image is when viewing it at near 100% in photoshop".

Personally, I NEVER use noise reduction on my images -- I've just never found a need for it. If folks have problem noise then 999 times out of 1000 it's because they're either under-exposing the captures and revealing noise when compensating in post-processing, or they're cropping excessively -- both are issues that they should be fixing at time of capture, not during PP

On to sharpening ...

Sharpening is mis-understood by many -- a common "myth" is that sharpening only needs to be applied once (usually at the end of the workflow). Unfortunately, sharpening is needed to counter softening due to a variety of reasons - and because these situations occur for DIFFERENT reasons, DIFFERENT sharpening protocols are needed to counter them. So lets work through them with some real-world examples ...

CAPTURE SHARPENING

When an image is captured, a degree of softness is introduced due to 3 things (1) the digitisation process (the process of converting a continuous scene into individual pixels) (2) the anti-aliasing ("blurring") filter fitted over the sensor by the manufacturer to prevent weird patterns appearing when the sampling interval of elements of a captured image approach multiples of the pixel spacing on the sensor, and (3) the demosaicing process as the captured information is "re-constructed" during processing.

Capture sharpening is only visible at a pixel level -- so one has to zoom in to 100% to be able to see it. In the grand scheme of things it won't make any difference to the final image if it's not done ... it just makes the image nicer to work on at high magnifications when one is doing professional retouching. Time for some examples ...

Take the following image - straight out of the camera, with no sharpening ... (unfortunately I've had to down-sample it for display here, but I've tried to convey the effect none-the-less).



And now - since capture sharpening needs to be viewed at 100% magnification, lets grab a portion of the image (100% crop) - perhaps the portion I'd see when working at 100% magnification on my monitor (ie when 1 pixel of the image uses 1 pixel on my monitor) ...



You might think it looks OK (if you're not in the habit of applying capture sharpening then this will no doubt look pretty normal), but it's not optimal. Take a look at the same 100% crop below, but with capture sharpening of 300% @ 0.3 pixel appplied ...



If you look closely at the above 2 examples, you'll see that the 2nd example is "clearer" or for want of a better word "sharper" (doh!). As I say -- it doesn't make any difference unless you're looking at it at 100%

CONTENT / CREATIVE SHARPENING

I mentioned above that capture sharpening is only visible when looking at the image at 100% magnification ... when we look at the WHOLE image at once on our monitors, it may surprise some people when I say we're not actually looking at the whole image ... for me, a typical image from my camera is around 3600 pixels wide by 5600 pixels high -- but my monitor can only display about 1900 pixels wide by 1080 pixels high - so when I'm looking at an image (especially a vertical one) - I'm only seeing a small fraction of the actual information contained in the image -- and thus it's not hard to see how capture sharpening (which is typically done at a radius of 0.3 pixel) just can't be seen. Take a look at the image below - it's the same as the very first image, but it's had capture sharpening applied ... you won't be able to see any real difference ...



So - to make our images "pop", we need to apply more sharpening, but it needs to be sharpening that applies to bigger areas so that we can see it when looking at the full resolution image, but displaying this FULL RESOLUTION image at a smaller size so that it fits on our screens. So take a look at the image below ... I've applied content / creative sharpening of 75% @ 6 pixels (I'd normally use something closer to 40% @ 4 pixels, but I wanted the difference to be more obvious).



In real-world terms, content / creative sharpening should reveal the same additional "clarity" to an image the capture sharpening does, but with the image displayed at a size that allows the entire image to be viewed (not just a small portion of it, as is the case with capture sharpening).

OUTPUT SHARPENING

OK - so we've applied our capture sharpening - and we've applied our content / creative sharpening - but at this point we still have a full-resolution image - and full-resolution images aren't suitable for posting online because they're just too big. To get around this, we down-sample them to make them smaller. The algorithm that's recommended for doing this in Photoshop is called "Bicubic Sharper" (and it does a pretty good job), but I've found a way that's better - I use plain old "bicubic", but add a touch of sharpening afterwards (typically 50 to 100% @ 0.3 pixel again). The result is subtle, but if you look closely, you'll be able to see the difference ...



and "viola" - we're done!

Hope this helps

[FrankMi]

I examine the photo I am sharpening at 100% magnification and sharpen as much as does not introduce artifacts that I can see anywhere on the photo.

Thanks, Tom. I also look for image halos. I find that the images created by my lower MP P&S camera can't stand near as much sharpening as the 14 MP DSLR before I start to get halos.

[FrankMi]

A third party method, like Neat Image is a much more effective way. It will blitz the noise without doing anywhere near so much damage to the sharpness.

Thanks Dave, I'll look into Neat Image and compare it to the other NR programs available.

[FrankMi]

The "short answer" is "yes", apply noise reduction before sharpening, so as to avoid sharpening the noise. Unfortunately, the "long answer" isn't quite that cut and dried ...

Hi Colin, thank you for the detailed reply with excellent examples that really help to see what is happening. Some friends of mine wanted the settings for the three sharpening situations, now I can forward them a much better response thanks to your tutorial! I appreciate the time and effort you put into this information!

[Lon Howard]

Thanks very much for the clarification, Colin. I do hope you can address a couple of minor points for me. As an alternative, can the capture sharpening be handled by a slight tweak of the sharpening slider in the detail panel of ACR, or a similar action in LR? And: for sharpening at all levels in your examples, may we assume that the threshold is set at zero? Thanks again!

[Colin Southern]

Thanks very much for the clarification, Colin.

You're very welcome.

I do hope you can address a couple of minor points for me.

Sure.

As an alternative, can the capture sharpening be handled by a slight tweak of the sharpening slider in the detail panel of ACR, or a similar action in LR?

There is a wise proverb "anything one CAN do in ACR, one SHOULD do in ACR", but in my opinion, this is the exception. The problem with capture sharpening in ACR is that it has a minimum radius of 0.5 pixels, and according to Canon, the radius should be 0.3 pixels. I've just setup an action button in Photoshop to apply capture sharpening, so it's literally just 1 click of the mouse as soon as the image has opened up.

And: for sharpening at all levels in your examples, may we assume that the threshold is set at zero? Thanks again!

Canon recommend 1 for base ISO, increasing to about 6 for high ISO settings, but I use 0 for base ISO, and take things on a case-by-case basis for high ISO settings.

Hope this helps

[Colin Southern]

Hi Colin, thank you for the detailed reply with excellent examples that really help to see what is happening. Some friends of mine wanted the settings for the three sharpening situations, now I can forward them a much better response thanks to your tutorial! I appreciate the time and effort you put into this information!

No worries Frank,

Just keep in mind though that content / creative sharpening numbers will vary depending on the image type and photographer's wishes.

[Lon Howard]

It was very helpful, Colin. Thanks!

[FrankMi]

Just keep in mind though that content / creative sharpening numbers will vary depending on the image type and photographer's wishes.

Absolutely! The numbers will get you in the ballpark but to hit a home run you may need to tweek them a bit. Thanks!

[wlou]

Oh my God! I think my mind just went blank. You know, like the TV screen when you loose reception...........

You are talking of 3 different level/kind of sharpening? Yes, I know I am a beginner photographer, and I cannot understand everything all at once. I feel a bit frustrated though, deh!

I use Lightroom, and I tought there was only one way to sharpen. Did you write a Tutorial on the subject? May be this was the tutorial and i just got lost in the subject.

If I could explain how I feel in image you would see am animal shaking vigourously a ton of water of her coat while shaking her head!

[Colin Southern]

Oh my God! I think my mind just went blank. You know, like the TV screen when you loose reception...........

You are talking of 3 different level/kind of sharpening? Yes, I know I am a beginner photographer, and I cannot understand everything all at once. I feel a bit frustrated though, deh!

I use Lightroom, and I tought there was only one way to sharpen. Did you write a Tutorial on the subject? May be this was the tutorial and i just got lost in the subject.

If I could explain how I feel in image you would see am animal shaking vigourously a ton of water of her coat while shaking her head!

Hi Louise,

Yes - correct sharpening needs up to 3 "doses" at various settings, at various times.

Yes - that was my "tutorial" (of sorts).

Sorry, really not sure of sharpening options in Lightroom (Lightroom doesn't fit my needs at all well I'm afraid) -- perhaps some of the LR folks can give you a definitive answer?

[FrankMi]

You are talking of 3 different level/kind of sharpening?

Hi Louise, as Colin wrote the reply, I'm sure he'll chime in when he sees your post. The short answer is Yes, there are typically three points in the post processing where you 'might' want to apply sharpening.
Capture Sharpening - is used to compensate for the initial changes made to the image from the internal camera's sensor image to the camera processed image (either to typically JPEG or the camera's export RAW) then onto the file format (DNG, PSD, TIFF, JPEG, etc.) you are using in your post processing software. These changes tend to soften the image so an initial 'capture sharpening' is done.

Creative or Content Sharpening - might be used on a specific object in an image but not usually the entire image so it is not a global change being made here.

Output Sharpening - is done when the image is changed again, typically to a different resolution or image size when we are ready to send the image to e-mail, the web, or a printer. As any resolution change can soften the image, a subtle sharpening may be needed to being the image back to the degree of sharpness it was prior to the changes made for the target output device.

This should get you started in understanding the three basic types of sharpening involved and hopefully Colin will chime in with further clarifications and corrections.

Edit update: Looks like Colin and I saw your post at about the same time!

[Colin Southern]

Hi Louise, as Colin wrote the reply, I'm sure he'll chime in when he sees your post.

Already beat you to it Frank

[The Blue Boy]

Think yourself lucky Frank!

Colin just told me to b*gger off and read a book!

"Real World Sharpening with Adobe Photoshop CS2 by Bruce Fraser"

Seriously good advice it was too! It's helped to give me a fundamental understanding of sharpening and noise reduction. And it will give you seriously good workflow options.

Cheers Colin!

[wlou]

Thank you everyone. I shall do some more reading too.