Sharpening luminance

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greenmorpher
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Sharpening luminance

Post by greenmorpher » Sat 10 Nov 2007 01:16

It has just been mentioned on the Canvas forum that the latest version of Graphic Converter has a "sharpening luminance" filter. Huh? Waht's that -- can anyone explain? And how do we do that in PL32?

Cheers, Geoff

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"Type & Layout: Are you communicating or just making pretty shapes" -- Revealed! The secrets of how you can use type and layout to turbocharge your messages in print. See the book at http://www.worsleypress.com

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Hoogo
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Post by Hoogo » Sat 10 Nov 2007 02:24

It sounds like the sharpening of the L-channel. Just choose "Lab" in the sharpen dialog and turn off a and b. This helps to avoid colorful halos when you sharpen a picture very strong and with a quite big radius.

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Post by greenmorpher » Sat 10 Nov 2007 13:49

Thanks, Hoogo. An interesting effect. Particularly useful on duller pictures, judging by a couple of small experiments I did.

Cheers, Geoff

Geoffrey Heard, Business Writer & Publisher

"Type & Layout: Are you communicating or just making pretty shapes" -- Revealed! The secrets of how you can use type and layout to turbocharge your messages in print. See the book at http://www.worsleypress.com

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Martin Stricker
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Post by Martin Stricker » Sat 10 Nov 2007 14:45

If your picture is in RGB-Mode, sharpening only the L-Channel may lead to some color changing. See the example below.

Image

Image

You can avoid this effect by choosing the HIS-Model and sharpening only the I-Channel (Intensity)or by first converting your picture to the Lab-Mode an then sharpening only the L-Channel.

I already told this effect to Gerhard, he said its not a bug.

Martin

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Hoogo
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Post by Hoogo » Sat 10 Nov 2007 15:22

Yes, the effect is hard to see in this case. When sharpening the L-channel you sometimes get impossible colors where L is black or white and a/b are colorful at the same time. In RGB keeping L correct is more important, in "real Lab" keeping a/b is more important. A good test-picture for this is a slightly blured red square on a blue background.

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Martin Stricker
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Post by Martin Stricker » Sat 10 Nov 2007 15:56

Hoogo wrote:Yes, the effect is hard to see in this case.
I can see this effect very well, but maybe your Monitor isn't calibrated :wink:

I measured the colour in the Owls beak, the gratest difference is in the R-Channel 71 instead of 80

Martin

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Post by Martin Huber » Sat 10 Nov 2007 19:08

Martin Stricker wrote:If your picture is in RGB-Mode, sharpening only the L-Channel may lead to some color changing. See the example below.
I can see the color change in your images, but I can't reproduce it myself. What filter and what settings did you use?

Martin

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Hoogo
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Post by Hoogo » Sat 10 Nov 2007 19:40

My monitor isn't calibrated, and it's quite angle-dependend. The bright feathers look a bit cooler in the sharpendes picture, do you mean that?

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Martin Stricker
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Post by Martin Stricker » Sat 10 Nov 2007 20:16

Martin Huber wrote: I can see the color change in your images, but I can't reproduce it myself. What filter and what settings did you use?
I don't know the exact values I did use. The effect starts at intensity values above 100% and gets stronger by increasing the intensity value.
Hoogo wrote:My monitor isn't calibrated, and it's quite angle-dependend. The bright feathers look a bit cooler in the sharpendes picture, do you mean that?
I would say there is a green color cast over the whole picture.

Martin

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greenmorpher
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Post by greenmorpher » Sun 11 Nov 2007 01:29

Hey!!! How can I incorporate a picture into a post?

Cheers, Geoff

Geoffrey Heard, Business Writer & Publisher

"Type & Layout: Are you communicating or just making pretty shapes" -- Revealed! The secrets of how you can use type and layout to turbocharge your messages in print. See the book at http://www.worsleypress.com

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Koyaanis
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Post by Koyaanis » Sun 11 Nov 2007 07:36

greenmorpher wrote:Hey!!! How can I incorporate a picture into a post?
Just enclose the URL to that photo (posted on the net somewhere) in the IMG formatting tags, like this:

[img]http://www.server.com/path/to/image.jpg[/img]

You can even post a photo as a clickable link by using the [url] tags, like this:

[url=http://www.server.com/path/to/page.html][img]http:www.server.com/path/to/image.jpg[/img][/url]

Normally that part where the img is embedded is where you would embed your text that you want to appear as your link. The above example is using the IMG tag instead of just text.

(normally used as [url=http://www.server.com/path/to/page.html]Here's the text that you want to describe that link.[/url] )

Using the second method here's a clickable graphic. Click on the image to get to PL32's homepage:

Image

This comes in handy if you only want to embed a thumbnail image to help out us poor dial-up people, and click on the thumb to get to the full size image, plus not breaking the message board's formatting by embedding too large of an image.

[url=http://www.server.com/path/to/full_size.jpg][img]http://www.server.com/path/to/thumb_size.jpg[/img][/url]

When editing your post the easiest way is to just copy/paste the url to your image in your message. highlight it in the editing area (click drag release over the URL), then click on the "Img" button above the editing area. It will automatically enclose the highlighted text in the proper IMG tags.

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Post by Martin Huber » Sun 11 Nov 2007 20:57

Martin Stricker wrote:I don't know the exact values I did use. The effect starts at intensity values above 100% and gets stronger by increasing the intensity value.
The intensity value is the problem. The filter itself delivers the same results, but in RGB images the filter result is converted to RGB and then written with 500% to the destination, and this is creating the color shift.

Martin

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Post by lutz » Tue 13 Nov 2007 04:05

Actually, I do not see the problem showing up in the owl image example.
Do you see the problem also when you use a duplicated sharpened layer set to luminance mode?

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Martin Stricker
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Post by Martin Stricker » Tue 13 Nov 2007 08:47

lutz wrote: Do you see the problem also when you use a duplicated sharpened layer set to luminance mode?
No, this is another way to workaround this problem. You can also use a working layer set to luminance mode.

Martin

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Loadus
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Post by Loadus » Thu 15 Nov 2007 16:03

Just quickly butting in to the conversation ...

About general sharpening - You can do quite strong sharpening with
Photoline by using different layer techniques to clarify the image - many
times the overall clarity of the tones is more effective than just using plain
sharpening.

(Sorry Martin S for using your image - this was just so delicious as a
demopic) The owl pic clarified with an overlay layer and finished off with
an Unsharp Mask filter (cranked up waaay above reasonable levels):

Image