GIMP

Troy Piggins wrote:

* Troy Piggins wrote :
* David J. Littleboy wrote :
"Alan Browne" wrote:

Ahem. Since in PS the effect of USM is immediately viewable everywhere
that the image is viewable, anything else would be (at least) an
additional step. See?

It's even better than that. When you scroll the image, the new part of the
image brought into view doesn't have USM applied. When you let go of the
scroll handle, USM gets applied. Seriously convenient.

Even cooler - Instead of using the basic USM supplied with GIMP
there's a (free of course) plugin called "sharpen (smart redux)"
where it adds the smart sharpening to another layer so you can
adjust the opacity to increase or decrease the effect. It only
targets edges so noise, bokeh etc isnt' sharpened.

This plugin can also use the "refocus" plugin to supplement the
above.

No idea if there's similar plugins for PS, and don't care. Just
letting you know there are better options than just USM for GIMP.

Dammit - forgot to change the Subject header.

shakes fist at Alan Browne /

I love it when you go all subtle.


--
Blinky
Killing all posts from Google Groups
The Usenet Improvement Project: http://improve-usenet.org
Need a new news feed? http://blinkynet.net/comp/newfeed.html

Alan Browne wrote:

AFAIK Tiff files have an assumed gamma when editing ro being displayed
or printed.

Not true.

You might come across a TIFF file that was stored linearily for example
and it will look really dark. Apply a gamma value to it (through an
editor or converter) and then store it after conversion. I don't know
if TIFF has a tag to store the gamma value.

In fact a TIFF image can, or not, contain a precision
gamma correction curve. Hence if you "come across a
TIFF file that was stored" with linear data and no gamma
curve, it will *not* look really dark. If it has a
gamma curve, that curve will be used for correction.

The display should end up looking exactly the same as
the image that was stored.

Of course whether a TIFF formatted image actually has a
gamma correction curve included is up to the software
that generates it. The software can just as easily
apply the correction and same the results as linear data
with exactly the same total effect.

What I'm on about with this 8 v 16 bit business however is how finely
stored the data is and hence how badly it is mangled in the lower bits
when represented as an 8 bit number (regardless of an exponential used
for visual representation).

The point is that 16 b/c contains data at a finer degree of granularity
which is what is needed during a chain of editing operations to reduce
artifacts created by the editing itself, operation after operation which
in photoshop can be as few as a 2 or 3 operations to dozens depending on
the whims of the photoshop user.

For the most part, that's all BS. Few people ever
manipulate a file sufficiently to actually see any such
artifacts. Indeed, Alan, the workflow that you posted
in other arcticles demonstrates that *you* would never
see such artifacts.

The actual problem is when tonal ranges are compressed
in any part of the range they are necessarily expanded
in some other part of the range. That leads to
posterization where expansion is done.

As long as such operations are avoided, or done in low
enough levels not to be significant, there simply is not
problem. Such operations are changes to exposure,
contrast and white balance, all of which really should
(regardless of the bit depth used in the output file) be
done in the RAW converter.

The in-memory representation of an image is up to the s/w designer. I
would hope that it is designed to lose as little dynamic resolution

What is "dynamic resolution"?

through successive operations as possible. And in all cases, the higher
the resolution, the better for the data before final output.

Which is why we don't particularly care for over
sharpened images... right?

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

In article , Troy Piggins
wrote:

Even cooler - Instead of using the basic USM supplied with GIMP
there's a (free of course) plugin called "sharpen (smart redux)"
where it adds the smart sharpening to another layer so you can
adjust the opacity to increase or decrease the effect. It only
targets edges so noise, bokeh etc isnt' sharpened.

This plugin can also use the "refocus" plugin to supplement the
above.

No idea if there's similar plugins for PS, and don't care. Just
letting you know there are better options than just USM for GIMP.

that sounds like adjustment layers, which has been built into photoshop
for over a decade, no extras required. with cs3 and smart objects, it
works with virtually any filter (e.g., gaussian blur, add/remove noise,
etc.), as well as third party plug-ins. it even works with the raw
data; go back and re-edit the raw, *after* other adjustments have been
made.

"David J. Littleboy" wrote:
"Alan Browne" wrote:

Ahem. Since in PS the effect of USM is immediately viewable everywhere
that the image is viewable, anything else would be (at least) an
additional step. See?

It's even better than that. When you scroll the image, the new part of the
image brought into view doesn't have USM applied. When you let go of the
scroll handle, USM gets applied. Seriously convenient.

Yes. That is exactly how GIMP works...

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

* nospam wrote :
In article , Troy Piggins
wrote:

Even cooler - Instead of using the basic USM supplied with GIMP
there's a (free of course) plugin called "sharpen (smart redux)"
where it adds the smart sharpening to another layer so you can
adjust the opacity to increase or decrease the effect. It only
targets edges so noise, bokeh etc isnt' sharpened.

This plugin can also use the "refocus" plugin to supplement the
above.

No idea if there's similar plugins for PS, and don't care. Just
letting you know there are better options than just USM for GIMP.

that sounds like adjustment layers, which has been built into photoshop
for over a decade, no extras required. with cs3 and smart objects, it
works with virtually any filter (e.g., gaussian blur, add/remove noise,
etc.), as well as third party plug-ins. it even works with the raw
data; go back and re-edit the raw, *after* other adjustments have been
made.

That sounds like you didn't read my last paragraph

--
Troy Piggins
I always appreciate critique.

Alan Browne wrote:
Floyd L. Davidson wrote:
snip

The USM is ________HORRIBLE________

Actually, it's great.

No. In PS CS3, a very light touch USM on an area of fine detail worked
fine. Identical settings (emphasis is on _light_) in gimp on the same
image created halos as well as deepened blacks with blocking up in
shadow areas. This likely includes further artifacts from the 8b/color
processing whereas in CS3 it is done at 16b/color.

Plain horrible.

With such wildly different opinions, I wonder what the differences in
the PS USM filter vs. the GIMP USM filter are. Does anyone know what
these filters *exactly* do, and in what respect they are different? At
least the controls seem to be the same, but perhaps the units differ.
-- Hans

Floyd L. Davidson wrote:
snip
The USM is ________HORRIBLE________
Actually, it's great.
No. In PS CS3, a very light touch USM on an area of fine detail worked
fine. Identical settings (emphasis is on _light_) in gimp on the same
image created halos as well as deepened blacks with blocking up in
shadow areas. This likely includes further artifacts from the 8b/color
processing whereas in CS3 it is done at 16b/color.

Plain horrible.
You *do* have to learn how to adjust it correctly. If
it
creates halos, back it off!
Been there many thousand times. I mention halos as it is one of the
signs of oversharpening that I look for... and why the little Gimp
window is so pathetically useless on large images.

If *you* are oversharpening, that is *not* the fault of the
tool.

The problem is that you expect "identical settings" to
result in
identical output. Obviously that is not correct.
I did consider that, but as the range of settings is the same I have to
assume they use the same parameters and process. A pixel radius can
only be a pixel radius. A level threshold can only be a level threshold
(although perhaps finer at 16 bit than 8 ... ah, you see what I mean!).

No, obviously you don't have a clue about what I mean or about
USM, either how it works or how to use it.

Not only learned them (esp. sharpening and USM) when I got my first film
scanner, about 10 years ago) but refined the technique. Not saying I
don't have anything to learn, but using USM is pretty old hat. I've
used USM on all images. On my 2 prior film scanners I've scanned nearly
10,000 slided and negatives.

Astounding.

(But kudos on attacking me rather than the 8b/c USM (etc.) of Gimp.

There is nothing wrong with the USM in GIMP. And whether it is
8 bit or 16 bit depth is totally irrelevant to USM.

The problem *is* you.

Why would I want to "attack" GIMP?

Try as I might, I could not get a result that resembled the Photoshop
version. First with the same settings (blocking up, halos, contrast
exagerated) and then with lighter sharpening weight and reduced
radius... Detail was obfuscated, not enhanced. It was, at best, clunky.

As to "performing" simple tasks, it is more direct and clear in
photoshop than in gimp. Yes, it can be learned, but I'd rather acheive
x work in the minimum number of steps and time.

See, it *is* you!

as possible by examining its effects throughout contrast areas in the
whole image. Gimp USM is not only a poor tool for this ... but it does
not do what it says it will do.
It does.
BZZZT. It can't. 8 b/c (1/256) is simply not as fine a level of detail
for image work as 16 (1/65536). That's just very simple integer math
doing its thing over and over, accumulating fine or coarse changes.

You clearly haven't got a clue about what actual differences
there are in using 8 bit or 16 bit. Sort of like claiming it is
quantization error... Nice big words that few people who read
this will actually have enough understanding of to know what
makes it so funny to those who do, but still hilarious none the
less.

Look up posterization. And gradients... and find out what
happens if you expand or compress the tonal range of a gradient.

Stick with coarse and try to have a nice life.

BTW, you can easily verify that too, with PhotoShop. Just put
it into 8 bit mode...

And that is my word to the OP: Gimp is free, but no bargain.

Obviously it is not for everyone... *you* should stick with
"simple" integers and interfaces both.

Hanz wrote:

With such wildly different opinions, I wonder what the differences in
the PS USM filter vs. the GIMP USM filter are. Does anyone know what
these filters *exactly* do, and in what respect they are different? At
least the controls seem to be the same, but perhaps the units differ.
-- Hans

Unsharp Mask is a generic technique, and does not in
itself imply a specific implementation algorithm. Hence
you are correct that the units differ. They usually
(but not always) have the same names, but that implies
the function not the magnitude.

Virtually all USM filters can be adjusted to give any
particular desired result, but each implementation will
require a unique set of paramaters.

It is worth noting too that with any given USM filter
the results that you see on a monitor will be different
than the results you see when the image is printed. And
with any given set of parameters the effects are
different for images with differing resolution.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd L. Davidson wrote:
Hanz wrote:
With such wildly different opinions, I wonder what the differences in
the PS USM filter vs. the GIMP USM filter are. Does anyone know what
these filters *exactly* do, and in what respect they are different? At
least the controls seem to be the same, but perhaps the units differ.
-- Hans

Unsharp Mask is a generic technique, and does not in
itself imply a specific implementation algorithm. Hence
you are correct that the units differ. They usually
(but not always) have the same names, but that implies
the function not the magnitude.

In a bit of experimentation I just did, I found that I get an almost
exact equivalence to a fairly typical Photoshop USM of:
0.3/150%/3 (radius/amount/levels)
by setting the Gimp to use:
0.3/0.6/3 (radius/amount/threshhold)

I *guessed* (wrong) that would mean I could play with either the radius
or level(threshhold) while holding the amount steady and get similar
results, but it was not so. As a test, I left the settings as shown
above and then changed Photoshop's radius to 3.0 instead of 0.3. When I
did the same in Gimp, the results were dramatically different and I had
to ramp the amount slider right up to get anywhere near a match. Once I
had got a similar sharpening result the halos in Gimp were noticeably wider.

So the three factors obviously interact quite differently in each
program - this doesn't necessarily mean anything good or bad, but it
does mean if you change from one to the other, you are going to have a
fair bit of re-learning/experimenting..

And I'm sorry, but for very subtle, low-level sharpening, I find the PS
controls/preview easier to use - in Gimp, the amount slider is way down
to the left for my sort of sharpening and small movements mean big
changes. I'm afraid my sharpening isn't that brutal...

Also, someone implied that Gimp toggled the preview on or off by simply
holding down the mouse or scroll bar..? not so in mine (2.4.6). You
need to check/uncheck the Preview box, and it only previews the effect
in the dialog box. In PS you merely have to hold the mouse button and
release it as you scroll around - nice.

Mark Thomas wrote:
Also, someone implied that Gimp toggled the preview on or off by simply
holding down the mouse or scroll bar..? not so in mine (2.4.6). You
need to check/uncheck the Preview box, and it only previews the effect
in the dialog box. In PS you merely have to hold the mouse button and
release it as you scroll around - nice.

Just move the mouse slightly (which will scroll the preview within the
image). You are describing for PS exactly what GIMP does.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)