Forums


Go Back   The TrekEarth Forums > TrekEarth Forum Home > Tips-Techniques

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old 01-07-2004, 01:43 PM
philip_coggan philip_coggan is offline
TE Junior Member
 
Join Date: Mar 2003
Posts: 247
Default Sharpening with Photoshop's Unsharp Mask

Here's what I do...

Basic principles:
(a) I'm going to end up with an image 645x430 pixels and at 72 dpi, and it's going to be strictly for the web - useless for printing.

(b) I'm going to do it by decreasing the size of the original image in 3 steps, sharpening at each step. So, I'm going to start with an image resolution of at least 288 pixels (72x2x2), because only then can I have three steps of decreasing size. I could begin with 72x3x3=648 pixels, or even larger, but 288 is the smallest I can start with.

Step 1:
(a) Go Image>Image Size.
(b) The dialogue box comes up. It has 2 check-boxes at the bottom, for Constrain Proportions and Resample Image. Untick the Resample Image box (the other box will also turn off automatically)
(c) Now go to the Resolution box, immediately above. It contains the current resolution of your image. Replace it with your sharpening resolution, i.e., 72x2x2=288, or 72x3x3=648, or whatever is closest to the existing resolution. (Warning: always go DOWN to find the sharpening resolution, never UP).
(d) Clik OK.
(e) Go Image>Image Size again. Re-tick the Resample Image box. Go to Document Size, and make sure the unit of measurement is Points - which are the same as pixels. Enter dimensions of 645x430 - or whatever you like, it doesn't really matter so long as it fits on the screen. Click OK.

Step 2: First sharpening
(a) Go Filter>Sharpen>Unsharp Mask. Set Amount (A) and Radius (R) as follows:
- if the image has lots of detail and/or is not very sharp, A=20 and R=40;
- if it contains little detail and/or is already sharp, A=10 and R=20;
- if it's in the middle, set values in the middle. Click OK.
(b) Go Image>Image Size, set Resolution to the mid-value - i.e., if you're operating on 72x2x2, you began at 288 and will now enter 144. Click OK.

Step 3: Second sharpening
(a) Go Filter>Sharpen>Unsharp Mask. Set Amount=40, Radius between 1.0 and 1.5. Click OK.
(b) Go Image>Image Size, set Resolution to 72. (Your Image Dimensions should now show 645x430 or whatever you chose earlier. If not, something has gone wrong!). Click OK.

Step 3: Third and final sharpening
(a) Filter>Sharpen>Unsharp Mask. Set Amount=20 to 30 (see what looks best), R=about 0.8. Click OK.

Most of all, avoid creating halos - the bright lines around the edges of objects, especially likely to form where dark masses border on light ones. If they start forming, reduce the Amount.

To save, I use File>Save For Web, set for JPEG at Maximum. I have the pre-view window set for 2-up, and use the Quality slider to control the final size of the file - there's little point in using 100%, you can't see the difference between that and, say, 80%.

Note that I've ignored the quality of your original image - but nothing can make a badly focussed photo sharp. The real first step is to take a sharp photo.
Reply With Quote
  #2  
Old 01-07-2004, 03:53 PM
timmiles timmiles is offline
TE Newbie
 
Join Date: Aug 2003
Posts: 93
Default Re: Sharpening with Photoshop's Unsharp Mask

very useful phillip. Any hints on sharpening for printing?
Reply With Quote
  #3  
Old 01-08-2004, 12:02 AM
philip_coggan philip_coggan is offline
TE Junior Member
 
Join Date: Mar 2003
Posts: 247
Default Correction and reply

I see I said to always go down when setting the resolution of the image you begin with for sharpening. This is impossible in most cases - my own camera delivers images at 180 dpi, and I wouldn't be able to follow my own guidelines. Just set the reolution for 288 and go from there :-).

As for printing - the same basic idea applies, of beginning with a large file and sharpening in a series of steps. But the final resolution for a print has to be about 300 dpi, otherwise it prints 'soft', out of focus. In order to arrive at a final resolution of 300 dpi, you'd have to start at something larger - and that would mean a huge file (although the smaller the photo, in terms of dimensions, the smaller the file).

So, to sharpen for print, begin with something at a resolution larger than 300 dpi and scale down progressively, but using the same settings for Amount and Radius as given above.

Hope you have success with this method - it was told me by a professional commercial photogrpaher, who should know :-).
Reply With Quote
  #4  
Old 01-08-2004, 01:33 AM
mitternacht mitternacht is offline
TE Junior Member
 
Join Date: Oct 2003
Posts: 120
Default Re: Sharpening with Photoshop's Unsharp Mask

Can I ask why you decrease resolutiong in steps? I can't understand why that would help?

I have another question concerning sharpness: What's the difference between Unsharp Mask and Sharpening? I use Corel Photopaint, not Photoshop, so I don't know if the function has the same name, but I guess there has to be some equivalent.
Reply With Quote
  #5  
Old 01-08-2004, 03:02 AM
philip_coggan philip_coggan is offline
TE Junior Member
 
Join Date: Mar 2003
Posts: 247
Default Re: Sharpening with Photoshop's Unsharp Mask

As I understand - and I only know what other people tell me - single-step sharpening, from, say 180 dpi (the resolution my camera produces when I download to the computer) down to 72 dpi (the final resolution on-screen) has 2 problems: First, it will almost surely introduce halos, especially where dark areas meet light areas, and second, it ignores the fact that different areas of the same image really need differetn sharpening settings - areas with little detail in them can stand far more sharpening than areas with a lot of detail. So the 3-step process does 2 things: it gives different sharpenings to the different areas of the photo (which is why it begins with Amount 20 and Radius 40 and then reverses this at the next step), and it 'shrinks' any halos it creates so that they ultimately become too fine to be readily visible.

As for Corel, I don't know anything about it. But I imagine that Sharpen is the equivalent of Unsharp Mask.
Reply With Quote
  #6  
Old 01-08-2004, 04:07 AM
ronners ronners is offline
TE Junior Member
 
Join Date: Dec 2002
Posts: 350
Default Re: Sharpening with Photoshop's Unsharp Mask

My usual technique is to switch to Lab mode BEFORE sharpening, and selecting the lightness channel. My experience is that this tends to avoid halos in color shots.
Reply With Quote
  #7  
Old 01-08-2004, 10:06 AM
philip_coggan philip_coggan is offline
TE Junior Member
 
Join Date: Mar 2003
Posts: 247
Default Re: Sharpening with Photoshop's Unsharp Mask

Yes, the approach I outlined is a basic one - there are ways of improving it even more.
Reply With Quote
  #8  
Old 01-08-2004, 11:21 AM
mitternacht mitternacht is offline
TE Junior Member
 
Join Date: Oct 2003
Posts: 120
Default Re: Sharpening with Photoshop's Unsharp Mask

Thank you for the answer Philip.

What I meant about Corel is that there is both Unsharp Mask and Sharpen, they are two different filters. The results are quite different, but I don't know what the technical difference is. Unsharp mask has a lot more tendency to introduce halos, while sharpen adds more noise.

I also have High Pass, Adaptive Unsharp and Directional sharpen, which I don't use.
Reply With Quote
  #9  
Old 01-08-2004, 01:47 PM
green green is offline
TE Expert
 
Join Date: Aug 2003
Posts: 1,348
Default Re: Sharpening with Photoshop's Unsharp Mask

Here is something that might help you to understand why UnSharpMask is call this way:

"Unsharp Masking is the way that everyone who works with digital image processing knows to sharpen their files. Of course the use of this ill-named tool has nothing to do either with masking, or unsharpness. It's just a carryover from the days when an unsharp negative was sandwiched with a sharp one to enhance edge contrast."

This quote is taken from a tutorial in Luminous landscape.
Reply With Quote
  #10  
Old 01-08-2004, 04:14 PM
Luko Luko is offline
TE Expert
 
Join Date: Apr 2003
Posts: 1,969
Default another refinement (endless approaches...)

Like Philip said, I also think there are many sharpening approaches and settings, Ron added the LAB way, as for myself I mix several things I found here and there on the web and I finally end to "step" sharpening (ie. sharpening a few times before getting a final result).

1st step - high radius sharpening : sharpening effect set to 20, radius to 40,
Effect : this seems to wash off any haze from the image. Not really a "sharpening" effect, more or less like adding overall contrast.

2nd step - sharpen the darker details : USM set on radius 0.3, effect on 200 or more, OK. THEN click on "Edit/fade sharpening" select "Darken" leave it to 100% ("Edition/estompage/obscurcir" in French).
Effect : sharpening dark details, choosing "darken" prevents from any halo effect, but the lighter details have not been sharpened yet, but let's see ...

...3rd step : same as 2nd step, but instead of clicking "darken" now choose "lighten" (éclaircir) and remove the halo moving back the effect % arrow towards 30 or 40%.
Effect : sharpening light details but still controling the halos.

Now it seems a bit complex and what is the benefit of that ? The great benefit about this solution is that you can control different values of sharpening on either dark or light parts.

Like all solutions it has its drawbacks, which is here that you cannot proceed in LAB mode!
Reply With Quote
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 09:09 PM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.


explore TREKEARTH