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"IMHO": Getting Into GIMP

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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Topic: "IMHO": Getting Into GIMP
    Posted: 14 April 2009 at 17:48


Getting Into GIMP
an article by alpha_in_exile




Introduction

     (taken from Turerkan's article A Day With GIMP with a few edits, you can pass this section if you read it) Being there, interpreting the scene, composing and clicking the shutter. Is this all you need in the way of making a good picture? Sadly it is not, and you have got a lot to do even after taking the shot.

     The other important aspect of photography is post processing. Photographers have varying opinions about processing, but I think its safe to say we all agree processing is a fundamental part of photography. It can't be left out, even when you don't manipulate the photo directly, it is still manipulated in many ways. For example, you can't avoid taking the picture through an optical lens, your sensor or film will have a tone response different than your eyes, and there is RAW conversion in digital photography. Even if you take “in camera JPEGs”, they still go through RAW conversion, but inside the camera.

     If manipulation is unavoidable, then the photographer will want to take control of the process if possible. We don't want our pictures to be just a randomly generated interpretation of the scene right? We want it to be our interpretation! This is where post processing comes in. Adding artistic values to a picture by means of processing requires a skill different than photography. However I believe that every photographer should at least be able to extract a realistic interpretation of the scene from his original shots.

Most image processing software is very expensive and hard to master. There are many programs to choose from, each appealing a different group of photographers. It may take many trials to find a program for your needs and your budget might not be enough for your favourite one. There are exceptions tough, thanks to the open source software community we have some free image processing programs available. The most developed and famous one is GIMP. It has a feature set nearly rivalling the Photoshop, state of the art in the industry.

  • GIMP; is free, both for commercial and personal use.

  • works under most operating systems, including Windows, Linux and Mac OS X.

  • is a general image processing program, very similar to Photoshop. You can use it for all graphical works.

  • is extendable by means of scripts, GIMP plugins and Photoshop plugins.

  • can handle most image formats.

  • can convert RAW files with the UFRaw plugin
  • However; it works in 8 bits per channel, only UFRaw can process 16 bits with RAW files which then are coverted to 8 bits.

  • Requires installing UFRaw for RAW compatibility. This is a trivial process though.

  • has an unusual user interface that may take time getting used to.




Links

The GIMP Project
Official GIMP Website | Documentation | Tutorials | Plugin Registry

Extras
Essential plug-in with many advanced post-procesing features, GREYC's Magic Image Converter
Compilation of all current scripts, GIMPfx Foundry
A general purpose high pass filter script, High Pass Filter
There is a Debian package for GIMP Plugin Registry items called gimp-plugin-registry
Plugin to enable usage of third party Adobe Photoshop Plug-ins, PSPI
For some Photoshop plug-ins to begin with, Flaming Pear | OptikVerve

Learning
Video Tutorials | Color Management | Smart Sharpening in HSV Colors | GIMP User Community


Edited by Turerkan - 05 May 2009 at 20:07
 



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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:49

Color Management


GIMP has been color managed since, I think, version 2.4.x. The options are found under the Edit menu, Preferences...



and the dialogue box looks something like this:



For in-depth info on color management choices, I like to recommend this tutorial (link is to the overview, which is followed by two more pages) (complete index to that site's tutorials is here).



Edited by Turerkan - 14 April 2009 at 18:58
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:49

Enabling 3rd-party Photoshop Plug-Ins (*.8bf files)


This is something I wish to dwell on. The GIMP is capable of employing a significant number of third-party Photoshop (abbreviated as PS) plug-ins, --those in the *.8bf format-- but only after first downloading and installing a special plug-in called PSPI.exe, which can be found here. Scroll to the bottom of that page, download the appropriate file for your operating system, and install the plug-in in GIMP's main plug-in directory (path -- C:\Program Files\GIMP-2.0\lib\gimp\2.0\plug-ins -- on a Windows machine with default install location). Then startup GIMP, and you'll find a new feature in the "Filters" menu:



click on that option, because you have another step to perform; you will be presented with a dialogue box for setting up the directory in which you will store all of the Photoshop plug-ins. Click in the field indicated below:



then click the folder/browse icon (circled below)



Navigate where you like & create a new folder for Photoshop plug-ins. Put all of your future *.8bf plug-ins in that location. (You can see the location I chose in the screen capture above).



Sample Plug-ins & Install


As noted on the home site of the PSPI plug-in, a few, totally free Photoshop plug-ins are available from Flaming Pear (scroll to the "free plugins"). Download the .zip file, and copy the *.8bf files to your Photoshop plug-ins directory. You don't need the extraneous *.html files or images from the zip file, just the *.8bf files. Whatever you choose to copy is thereby installed, and GIMP will recognize the new filter(s) when you next start the program. Here I've copied just the one filter, and it now appears in the Filters menu, under Flaming Pear:



One, free, third-party Photoshop plug-in I occasionally make use of is Virtual Photographer. I learned of VP from a sharpening tutorial here on Dyxum, called "Meet Frank," written by MiPr. It is, unfortunately, a Windows-only plug-in (the difference, I guess, is that VP relies upon a number of Win-only support files that won't work in Linux).

To install this particular plug-in, download the installation program, then direct the installer to put the plug-in file in your Photoshop plug-ins directory as created in the process outlined above. Restart GIMP, and you'll find the new filter, just so:



It should be noted that VP only works on color/RGB images, not on grayscale images. So you have to make sure the image "mode" is set to RGB, otherwise the plug-in will be 'grayed out' or inaccessible.



Edited by Turerkan - 15 April 2009 at 11:29
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:50

Installing New Scripts


I once set out to do some high-pass sharpening, and realized GIMP does not come with a simple high-pass filter. So I did a search in the GIMP Plug-In Registry, and, fortunately, there is one available, right here.

Adding a script is much the same as adding a filter. Download that .scm file, and place/copy it into GIMP's Scripts directory (typically: C:\Program Files\GIMP-2.0\share\gimp\2.0\scripts). Start GIMP, and you'll find the new filter under Filters --> Generic --> High Pass Filter.



Edited by Turerkan - 14 April 2009 at 18:59
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:50

Sharpening: Unsharp Masking (USM)


GIMP's USM is located under Filters --> Enhance --> Unsharp Mask. The basic parameters look much the same as in PS, however the numbers/multipliers are different, so don't try to apply Photoshop settings directly here. Of course, if you do try PS's (much higher) numbers, you'll immediately notice the difference in the preview window.

Polyglot's recommended initial pass, as you can see, is conservative (untouched image is the one on the right, behind the USM window):



Setting the threshold at 20 prevents sharpening of the noise in the shadow area (if you can't immediately see the sharpening, compare the patches of writing reflected on the pen).

Another approach is to apply a stronger USM, then 'fade' the effect. Immediately after you apply the USM [or certain other actions], an option to 'Fade [whatever]' will appear in the Edit menu.





(notice you can also set the blend mode, default is 'replace')

the effect (left- high USM [before], right- faded USM [after])




Edited by Turerkan - 15 April 2009 at 11:30
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:50

Sharpening: Highpass Sharpening


If you installed the highpass sharpening script according to the instructions above, apply it as you would in PS: with your image open, start the filter -- you will want to keep the "keep original layer?" box checked, otherwise your original image will get replaced by the output of the filter -- bring up your Layers dialogue & you will find that you now have two layers, the orig. image and the new layer with the high-pass version. Set the high-pass layer blend mode to "hard light." Your image should be sharper/contrastier. Flatten the image & save as a JPG.

before


after


You will find that the high-pass filter will, with some images, darken the whole image too much, or perhaps even enhance noise. This can be remedied somewhat by adjusting the filter's parameters. Experience will teach you which images will benefit, and which ones won't.



Edited by Turerkan - 05 May 2009 at 20:19
 



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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2009 at 18:53

Sharpening: Luminance Sharpening using L*A*B color


There's a decent tutorial on the GIMP website for "smart sharpening" using HSV decomposition, but it has a couple of issues. One, it was written for an older iteration of GIMP, and two, there are a couple of steps that are incompletely described. The HSV approach also sharpened parts of my image that I did not want sharpened. So I worked up a L*A*B approach.

HSV = Hue, Saturation, Value
L*A*B = Luminance, color channel "A," and color channel "B" (IIRC)

In a noisy image, even a slightly noisy image, the simple application of USM can cause sharpening of the noise, which can make the whole image appear noisier. Setting a high threshold in USM can sometimes help, but then you may fail to sharpen things you do want to sharpen. Or you can sharpen small selections, or sharpen using masks. But by separating out the luminance channel, it is possible to sharpen in just the luminance channel, thus preventing any sharpening of color/chroma noise.

Here is the photo to be sharpened:



There's very little that's in focus, in this shot, so it is a little difficult to sharpen just the in-focus parts and not any of the OOF parts. USM with a high threshold works moderately well, but I found that a judicious use of luminance sharpening through L*A*B could work even better.

The first step is to "decompose" the image into its L*A*B components.



You'll be given a dialogue box with a number of options. Choose LAB. Leave the 'decompose as layers' box checked, as you will want to work on the L(uminance) layer only. Leave the second box, 'foreground as registration color' unchecked.



Now, bring up the Layers dock (CTRL + L) or (ver. 2.6.x) under menus Windows-->Dockable Dialogs-->Layers, and click on the 'eye' symbols next to channels A and B, if you like, to make them invisible.



In order to sharpen only the edges in the image, we need to mask off everything that is not a hard edge. First, duplicate the "L" layer, and name the layer "sharpening" or something to differentiate it.



Then employ the Edge-detect filter (Filters-->Edge-detect-->Edge) on the sharpening layer only.



The Edge filter attempts to filter out anything that is not a strong edge, making non-edged sections black, and edges white; the image in the preview window will show you what elements are being detected as edges. Adjust the "Amount" parameter until you are satisfied that only the edges you want to sharpen are being emphasized.



The layer will now be black with white highlights. For my image, the layer looks like this:



You should be able to see not only the points on each spike, but also lots of much smaller details or points that were captured by the edge filter. I don't want all of that stuff sharpened, though. So it is recommended, but not absolutely necessary with all photos, to adjust the Levels (menu: Colors-->Levels), moving the black point up and the white point down, to make your edges whiter and your non-edges (or the detail you don't want sharpened) darker.



As you can see, I moved the black point up to 11 and the white point down to 170. Remember this is just your sharpening layer, not your final image. Notice that the many small white points, which were present after I first applied the edge filter, have now faded to black, so I have a nice black background and, in isolation, bright white edges.

Once you've isolated the edges you want to sharpen, then apply a slight gaussian blur (Filters-->Blur-->Gaussian Blur) to widen the edges a bit.



(sorry I didn't get part of the image in the preview window!)

The "smart sharpening" tutorial from the GIMP website suggests again adjusting the levels after the application of gaussian blur. The blurring does darken the 'halo' around your edges, and you want them fairly white for the next step, so it is recommended to again raise your black point and lower your white point as needed.

Now, go to your "L" layer (bring up your Layers dialog with CTRL+L and select the L layer), and add a layer mask (either by right-clicking on the L layer, or by going to the menus: Layer-->Mask-->Add Layer Mask).

Here I've done it by right-clicking and selecting from the menu:


Mask type: choose White (full opacity)


Your layers will now look like this:



Next, go back to your sharpening layer, select all (CTRL+A or menus: Edit-->Select All) then copy (CTRL+C or Edit-->Copy).

Now return you your L layer, and, specifically, click on your layer mask (the small window/rectangle to the right on your L layer)...



..."paste" the image into the mask. Anchor the pasted image by clicking outside your canvas, or by right-clicking on the layer mask in the Layers dialog box and selecting "anchor layer" like this:

[ IMG]http://i8.photobucket.com/albums/a43/xj-xile/LABUSMdemoanchorlayer.jpg[/IMG ]

Once anchored, your layer mask should look like your sharpening layer, in the Layers dialog box.



Once your sharpening layer has been copied into the layer mask on the L layer, you should delete the "sharpening layer." Later, when we recompose the image, you can have only three layers.

The next part is great -- right-click on the layer mask and choose "Mask to Selection" (or menus: Layer-->Mask-->Mask to Selection).



This will select -- on the L layer -- only the white edges from your layer mask. It is now safe to delete the layer mask (right-click & choose 'delete layer mask' or menus: Layer-->Mask-->Delete Layer Mask). Only the mask!

[ IMG]http://i8.photobucket.com/albums/a43/xj-xile/LABUSMdemodelmask.jpg[/IMG ]

What you are left with is the L layer with 'marching ants' showing the selected edges. This is where you apply USM, which will only affect the selected edges and only affect the luminance channel.

[it seems I forgot a screen capture of the image with marching ants - to be supplied tomorrow]

As the old GIMP "smart sharpening" tutorial states, you will find that you can use a much stronger application of USM without introducing artefacts. I used settings of: Radius 0.6, Amount 1.88, Threshold 4. These are still very conservative settings; I based them on the type of image I'm editing, and the thought that I may print this image very large. If I print it small, though, I'll probably want to do more sharpening (maybe just USM + Fade).

When you've finished sharpening, you must recompose the image (menus: Colors-->Components-->Recompose). This will return you to an RGB color version of your image (in the same window as your original image).

[also forgot to upload the screenshots of the Recompose process]

Below are some 100% crops for comparison.





(image on left the font is hard to read -- USM settings were R 0.5, Amt 0.30, T 20 for first pass, R 0.5, Amt 0.74, T 20 for the second pass)



USM faded = USM applied with settings R 0.5, Amt 1.36, T 20 and faded to 80%. It seems to equal or even better the L*A*B version for clarity of detail, which may be my fault -- a function of the conservative USM settings I used in the L*A*B version, or too-low threshold, or some other fault -- or it may be simply a superior method.

[I'll have to update this post in stages by editing the post over & over again... stay tuned!] [I have yet to test the luminance sharpen plugins, and I think I set too low a threshold for the USM in the L*A*B version, or I skipped a step (conversion to greyscale of the sharpening layer) so may have darkened the image somewhat, looking at the comparison crops]

Edited by Turerkan - 09 May 2009 at 20:49
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2009 at 23:15
I would like to thank alpha_in_exile, and all others who participated the GIMP & open source 'ware as it is today topic. Without them, this wouldn't be possible.

I hope this article will help promote open source software and GIMP in general. Meanwhile i also started a themed view topic called GIMPed Photos!, everyone is invited!
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Post Options Post Options   Quote Micholand Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 20:04
Thanks for putting in the time and effort to make this for us, Matthew|alpha_in_exile!

Maybe it's also worth to put the various sharphening techniques mentioned into one big article as those methods aren't really GIMP specific, then you may get more attention and feedback, too - sometime ago we did start these case study writings, looks like this would be a nice follow-up

[EDIT]: Of course credit goes to Matthew|alpha_in_exile and not Mr. T

Edited by Micholand - 09 May 2009 at 21:25
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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 20:53
micholand: you should thank alpha_in_exile! i didn't do much compare to him. the idea here was taking attention at gimp, letting photographers know there is an alternative, especially to those who can't afford the big ones. An article about sharpening sounds good but it's not really the spirit of this one. However, if such a project comes to life, i'm sure we will use alpha_in_exile's great suggestions here.

thanks for the bump btw, this topic needed it lol:D
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Post Options Post Options   Quote fmajor Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 21:09
Thanks SO much for this!

I am usually pretty inclined to learn new software, but photo-editing (and add to that video-editing too) is proving to be a stumbling block for me.

In fact, i just compiled a new PC to handle my perceived graphic editing needs:

CPU: Intel i7 920
RAM: Corsair 6GB 1600Mhz
GPU: eVGA GeForce GTX285 SC Edition
SYS HDD: WD Velociraptor 300GB 10,000RPM
Storage HDD: WD Caviar Black 1TB 7,200RPM
PSU: Corsair 850TX
Case: CoolerMaster 690

IF there was a place for GIMP tips here on my favorite (only?) photo website, that would be excellent.
|KM 7D|a200|Sig 15-30mm| Min 28-85mm|Min 28-135mm| Min 70-210mm F4|S75-300|S18-70

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Post Options Post Options   Quote Turerkan Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 22:12
wow... your system really rocks:)
for gimp tips, just ask away in the darkroom forum and we GIMP friends will reply;)
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Post Options Post Options   Quote redmalloc Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 22:43
Originally posted by fmajor fmajor wrote:


CPU: Intel i7 920
RAM: Corsair 6GB 1600Mhz
GPU: eVGA GeForce GTX285 SC Edition
SYS HDD: WD Velociraptor 300GB 10,000RPM
Storage HDD: WD Caviar Black 1TB 7,200RPM
PSU: Corsair 850TX
Case: CoolerMaster 690


Wow, similar to my new system. Although I used the previous gen quad cpu, since the i7 wasn't out yet. I fretted over getting a solid state drive, but went with the raptor in the end. Next time around I'm sure we will be booting from SSD. It is really a pleasure doing image processing with this system!

--

Anyway, thanks for creating this thread! I thought I was going be so so helpful by posting a link to alpha_in_exile's great thread

Edited by redmalloc - 09 May 2009 at 22:44
T: 17-50 70-200 100-300

M: 7D 16 28-135 50M 85 70-210

S: A700
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Post Options Post Options   Quote fmajor Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 23:21
Thx Turerkan/Redmalloc!

I don't wanna hi-jack RE: my PC, but am just WAY thankful for this thread. I'll be bouncing there (darkroom forum that is!) for the how to's.... There's also a flickr Group dedicated to/for GIMP and it's also quite helpful. I just gotta do it!

I need learn to use editing software and utterly refuse to splash for photoshop - if for no other reason than to not be a lemming... Also, i LIKE how GIMP is open-source and the free-thinking it encourages.

I know i'm missing out on a lot of photos b/c i don't know how to PP and i'm looking to forward - sorta - to spending the effort to learn.
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