4 image mosaic Moon 08-02-09

Out of genuine curiosity why should you do this?

This wrecked my head when I was working on my lunar images. I used to sharpen my images along with all other processing on the full size image. I mean, this really does sound like the logical thing to do, right? Then, when I re-sized the image significantly downwards to make them more web-friendly, they lost their sharpness. I was puzzled.

My understanding of it is as follows:
Sharpening is based on pixel size. This is where if differs from contrast, brightness and colour. If you have a large image and reduce it to say 25% of the original size, you are losing your sharpening, but not your brightness, contrast and colour. As the image will have softened, you will then need to resharpen. However, sharpening also introduces artifacts and noise into an image. So, when you apply sharpening a second time, you are applying sharpening on top of the side-effects of the original sharpening.

So, you might think, how about if I apply unsharp mask to the original image but with a larger radius and more sharpening effect so as to counteract the resizing effect? This only introduces more artifacts and noise into the image.

IMHO, once the image is re-sized, only a radius of 1-2 pixels should be used and the strength should rarely exceed 100%.

The problem of course, which I suffer from ALL the time, is that my eyes get so used to the image as I am processing it, that I don't notice this "small" amount of sharpening too much and feel I need to apply more. Then, when I walk away from the PC and come back an hour later, I see the image with very different eyes and excessive sharpening jumps out a mile then.

Have I explained this in a manner that makes sense?

Michael.

Just came acros this:
www.earthboundlight.com/phototips/unsharp-mask.html

(explains it a bit better than I did).

Just to clarify BTW what i was trying to say:
1. Do all normal processing.
2. Resize image.
3. Apply sharpening image then.

Michael.

Love the images James,excellent quality. Great advice from the lads there. One thing I find useful is to feather the selection after you decide on the areas you wish to sharpen. Normally I, use a value between 25 and 100 pixels, could be smaller or larger, depending on the size of the selection, and the resolution of the image you are working with. A case of trusting a bit of experimentation. This will fade out the effect of sharpening in the outer regions, and "hopefully" blend it into the image. I hope this is of help.

The problem of course, which I suffer from ALL the time, is that my eyes get so used to the image as I am processing it, that I don't notice this "small" amount of sharpening too much and feel I need to apply more. Then, when I walk away from the PC and come back an hour later, I see the image with very different eyes and excessive sharpening jumps out a mile then.

Have I explained this in a manner that makes sense?

Micheal... I suffer from that all the time...... is there a cure? and as a result I end up with about 20 "final images", not remembering which is the real one. The only fix I know of, to date, is "sleeping on it" and looking at the images with fresh eyes.... the next day, does anyone have any alternative suggestions? Reminds me of my music recording days where the Producer used to get in a "fresh ear" (later in the evening) to listen to the mix, after a day of listening to us "rock it up"!!! I'd say Frank could empathise with that.

James, you have done an excellent job capturing the Full Moon there, which is not an easy image to photograph. If only my first attempts were half as good. Well done

I started out just using a hand held basic camera, hand-held to the eyepiece, with very questionable results, and thanks to the advice and guidance from the members here, I am getting better images. Keep at it and I look forward to seeing Saturn from you soon.

Best regards

Steve

Ah,
Right Mike.
I see now.
I've actually done that myself to create 'web friendly'
(for the want of a better term) images.
If you ever want to print out images (and I do all the time)
you need to work in full size or else you will loose quality.
I've actually done exactly as you say there to make some
images look better when displayed on the web / pc.
So maybe the suggestion should be to keep your master image.
Then create your web version and if you want to ever print it
use the large one.

As for going googly-eyed from processing.
We've all done it right?
Sat there for hours in front of the screen,
tweak a level here, push a gradient there - madness.

Steve,
I know only too well what you're on about with mixing in the studio.
We had a nutty engineer once that spent 4 hours getting the
snare drum 'just right' I thought I was going to loose my mind
listening to it.
I think I can still hear it.

As for resting your eyes to see it fresh,
the only way is to walk away for a few hours and do something else,
You'd be amazed how different something can look with 'fresh eyes'
as the lads say.

Steve,
I know only too well what you're on about with mixing in the studio.
We had a nutty engineer once that spent 4 hours getting the
snare drum 'just right' I thought I was going to loose my mind
listening to it.
I think I can still hear it.

..... jaysus Frank... I think I can still hear that snare drum..... either a nutty sound engineer or perfection?? I Still agree though, .... it wrecked my fragile head listeneing to it continue forever!!!

Must have been the same engineer????

Best regards

Steve

... forgot to mention, I wasn't the Drummer ... I was the Bass player :dry: .. hence the interest in astronomy ?.... Bass rhymes with space!... ??????????????