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6./ZG26_5tuka

Custom Alpha Channel Tutorial for Gimp (advanced skinners)

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This thread shall only serve advanced skinners using Gimp 2.8.4 and higher. I will not cover any basic skinning tutorials in here. If you have any questions about importing and modifying skins for IL-2 Battle of Stalingrad pls visit this thread: http://forum.il2stur...-skinning-gimp/
 
Since my recent posts about basic Alpha channel work have been moved / mashed up I decided to create a new thread covering all steps of modifying Alpha channels in Gimp exclusively. :)

I'm sry for this large post but I wanted to make sure to cover every step together with proper visual material to help understanding the working process with Alpha channels.
 
First: Whats an Alpha channel?
 
Alpha channels are greyscale textures of the actual aircraft skin used to model surface reflections ingame. Unlike the actual skin layers the Alpha channel is hidden and needs to be accessed before editing.
 
How do I access the Alpha channel?
 
To access your alpha channel you have to switch from the "Layer's dialog" to the "Channels" window in your righthand toolbar. To do so press the small tab right to the "Layers dialog" tab in the upper toolbar.
3pp528xo.jpg
 
As you can see we have 5 channels including 2 called "Alpha". The one we're looking for is "Alpha 1", don't confuse them!

Now select "Alpha 1" via  left mouse click. Be sure Gimp automaticly deselects all upper channels:
iuhkdmwp.jpg
 
Copy the "Alpha 1" channel to your clipboard by pressing ctrl+c and switch back to the "Layers dialog" via the left tab. Than create a new layer (name is irrelevant) and press ctrl+v to paste your copied Alpha 1 channel into your new layer.
 
Hint: It will first appear in floating selection. To make it settle press left click outside the image's boarder or press right click on the "floating selection" tab -> "anker layer".
 
After that you should get this:
s38qoig7.jpg
At this point you can start editing it to your personal liking.

 

How do I modify the Alpha channel?
 
There are some things you have too keep in mind before customizing your Alpha channel. The game only reads the Alpha channel as a greyscale texture even though you can colour it. It does only account for the white value of the Alpha which means different colours have no effect.
 
Also your Alpha channel needs to have 100% occopacity. If you lower your Alpha channel's occopacity Gimp will automaticly compensate for that once exporting the skin.
As previously said the Alpha channel serves the simulation of reflections via grey tones ingame. Different tones of grey feauture different reflection characteristics, which you sould take into account.
 
In order to determine a certain grey tone you have to use the colour definition tool.
3xnw8lua.jpg
Here you can see a bunch of values defining a colour. The underlined number is the "white value" which is what I recommend using for modeling grey tones. As in this example  value of 35 tells us our current grey tone consist of 35% white and 65% black, means it's a dark grey. You can alternatively use the RGB values below though I find the "value" to be more the more convinient refference to work with.
 
Some basic orientation for the effects of grey tones:
Tone            Value                           Appearance                                
white             100                              Totally matt
light grey     51-90        the brighter the more reflections, less shine
mid grey        50        optimal combination of reflections and shine
dark grey    49-10         the darker the less reflections, more glow
black              0                                 transparent
 
Visual demonstration of the effects:

Note: In this demo I used geys with value of 100 for the fin, 75 for the right wing, 50 for the fuselage, 25 for the left wings and 0 for the left stabilizer.

 

Moving on you can use multiple technics to modify your Alpha channel. You can equally use the selection or lasso tool for selecting certain parts of the skin and colouring them with the pen or filler tool or copy content of skin layers and colour them grey, than insert them into your Alpha. No matter what mehtod you chose be sure to create several layers in order to reverse or corrcet your seps as nessecary.


To give you an example I'll use my silver IL-2 "Red 2" skin starting off with the basic Alpha channel texture:

yi6ug8yg.jpg

 

First of all I noticed this grey creates too much shine for my taste so I darkened all parts of the airframe I want to be more matt. In this case it's wooden parts of the aircraft for example.

reobssya.jpg

 

Now I want to make metallic parts more siny and reflective. This is done by lighting up metallic parts with a lighter grey (you don't have to use any gradient pattern as I did, simple lighter grey areas are fair enought).

iibthd5i.jpg

 

Following the same principle I continued working with this pattern to adjust details by either highlighting or darken them. This for example is my final Alpha channel feauturing several added details like weathering, decals ect.

8kdfstec.jpg

This stage basicly shows the final Alpha channel. If you are interested to see the final skin check this link: http://forum.il2stur...ns/#entry231136

 

Some hints: - Details like exhaust gases, weathering and panel lines that require matt finish ingame are best done by using very dark grey (value 5). If you go for a grey below value 4 it will be transparent inagme!

- Shiny parts like bare metal are best modeled with a value 50-60 grey. Mind the game enigne can not simulate real bare metal look, thus you can only try maximise the reflection effects.

- Use some logic to model a realitsic Alpha. If your aircraft feautures wooden chips copy them into your Alpha to adjust it accordingly and make them matt. Also mind the different kinds of paints used to coluor aircaft having different reflection characteristcs.

 

You can easily pull off a lot of detail working with your Alpha channel this way so don't neglect this part.

 

How do I apply my customized Alpha channel to my skin?

 

Applying your basicly works the same as accessing it. First you have to merge all your Alpha layers into your final Alpha texture, than ctrl+c.

 

Now switch back to the "channel's dialog" via the upper tab of the righthand toolbar. Select "Alpha 1" and check all other channels are deselected. After that press ctrl+v and settle it by pressing left click outside your image boarder.

 

You should now see the small preview image changing if done correctly. At this stage you're ready to export your skin.

 

How do I export my skin with my custom Alpha channel?

 

To export yur skin first disable your custom Alpha texture in the "layers dialog". Than merge your skin layers as usual.

 

Hint: Due to different layer sizes in the official templates some skins tend to have corrupted resolutions after using the "flatten image" function. I strongly advise you scroll down to the bottom image (usually called "Background", rightclick on it and press "Merge Visible Layers".

6bvcv8v4.jpg

As the new window appears press "Clipped to bottom Layer" and press "ok". This way all layers get adjusted accordingly to your bottom layer's resolution and your skin will not be corrupted.

 

Once your skin has been merged press right click on the skin layer and "Add Layer Mask". A new window will pop up:

fncfm5hr.jpg

Select "Channel" and chose "Alpha 1" out of the selection, than press "Add". As result your skin should appear semi transparent which means the Alpha Channel has been applied sucesfully.


Now you only need to export your skin as .dds and you're good to go!

 

I hope you enjoyed this guide and understood the editing process and the function of Alpha Channels in Battle of Stalingrad! If you have any questions pls feel free to ask!

Edited by Stab/JG26_5tuka
  • Thanks 1
  • Upvote 11

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Thx guys! I'd also like request to make it stcky :)

 

Unfortunately I couldn't squeeze out all spelling mistakes due to the editing function being bugged for large posts like this. Still hope the information is usefull. :salute:

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I'm sry for this large post but I wanted to make sure to cover every step together with proper visual material to help understanding the working process with Alpha channels.

 

This is wonderful information regarding the alpha 1 channel, (Grey scale masks), or another way of looking at it, (correct me please if of track)  the difference in the planes materials reflective properties via tone. or translucent effects. I gave you a thumbs up, excellent and clear tutorial btw Stab/JG26_5tuka.
 
In real life: One thing I noticed when sighting paint on metal military land and air vehicles, is that the finish appeared satin. I have not seen a painted WW2 wooden uncut , (not sanded between coats), vehicle in real life yet, but a guess would be some where between matte and eggshell depending on the number of coats applied and temp.
Example of High gloss would be: A new polished aluminium surface and semi-gloss after a few sorties or where fabric  has rubbed the paint coat off.  I really liked the footage you added also, as it shows your examples in engine.  :salute:  and thank you very much for your time.

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True military paint isn't as refective as for example civil aircraft gloss paint. While not being a WW2 warbird we have a Do 27 with original Bundeswehr paint at or airstrip. It does still reflect light but not in a way high gloss painted planes do (which seems logical since it's a camouflage paint after all).

 

Still WW2 planes used some sort of reflective lacquer to protect the coloured layers of the actual paint as well as improve aircraft performance. It also reduced the ammount of heat stress of the airframe and was a vital part of the overall paint shop, which if lacking it would have worn out pretty quickly.

 

Ingame a 32 - 38 value grey does seem to catch this effect quite well. Everything below does seem too matt.

 

It also highly depends on the light setting. If we take a winter setting suhc as in Stalingrad where sunlight is very intense reflections should be as well.

 

As I don't have any good pictures from warbirds I'll use this as an example:

aircrafts_messerschmitt_bf109_me109_desk

Edited by Stab/JG26_5tuka

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From what I understand, (please correct me, as we are all here to learn) the value of 32 - 38 is on the darker scale, meaning partual transparency (with mask applied), and or if for example:  ffffff (white) was used, it would show the original image, (with mask applied).

Visual rough example would look something like this:

The first image is a scale from white to black within the greyscale bitmap. The second image is the original image, and the third image has the mask applied.

post-12377-0-89241200-1427372040_thumb.jpg post-12377-0-73314300-1427372048_thumb.jpg post-12377-0-59047900-1427372044_thumb.jpg

 

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From what I understand, (please correct me, as we are all here to learn) the value of 32 - 38 is on the darker scale, meaning partual transparency (with mask applied), and or if for example:  ffffff (white) was used, it would show the original image, (with mask applied).

Visual rough example would look something like this:

The first image is a scale from white to black within the greyscale bitmap. The second image is the original image, and the third image has the mask applied.

Yes, you are totally right. The grey tone basicly determines the transparency, which again is translated into different kinds of reflections and intensity ingame.

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I think I deleted the alpha chanel. 

 

Is it possible to restore it ??? I finished the paint work and I would like to have the alpha channel back if it is possible :)

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5tuka,

 

Now that I have recreated new skins for a few aircraft, I decided to finally give your Alpha Channel Procedure a try.  If you remember, you tried to help me through it in another thread.  At the time I was using GIMP and you PS.  That thread was moved and you ended up creating this post specifically using GIMP.

 

To start with I have GIMP v2.8.14 which, according to their web site, is the latest version.

 

Here is what happened.  I opened my file, in the Channel tab I deselected the upper channels and selected Alpha 1.  I then copied the Alpha1 channel and pasted it into the Layer tab.  I right clicked on the floating selection and when I click on Anchor Layer, the floating selection disappears.  It does not create a new layer.  It does not ask me to name it, etc.  It is just gone.  So, I am pretty much dead in the water before I even start.  If memory serves me correctly this was the same issue I had before.

 

Oh well...

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Ummm...  I may have something.

 

Once I paste the Alpha1 to the Layer tab, I clicked and dragged the Floating Selection (Painted Layer) to the image.  It created a layer called Painted Layer Copy which shows in gray like you sample of the anchored alpha channel.

 

I then Anchor the floating Selection and it disappears, as mentioned before, but the gray Painted Layer Copy remains.

 

I will attempt to continue with your procedure using this layer and see what happens.

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5tuka,

 

I continued on with your procedure using the Alpha layer.  I lightened one wing and darkened the other as a test.  Bottom line, it works.  Now I can adjust my skins to something other than all shiny or all flat.  Thanks!

 

I found that when pasting the Alpha layer back to the Alpha1 channel there was another issue I had to overcome.  Instead of updating the channel, for some reason, it creates a Floating Selection back in the Layer tab.  I remember this from before also.

 

What I did to overcome this was similar to the fix going the other way.  I simply dragged the Alpha layer from the Layer tab to the Channel tab and down by the Alpha1 channel.  It created a new Alpha channel which I brought to the top and renamed.  It had a 100% opacity which i kept.  I deleted the other Alpha1 channel.  This new Alpha channel was used when I added a Layer Mask to the merged layers before export.

 

When I loaded the new skin into the game the results were striking.

 

S!

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Hey Stick, sry for the late reply. I'm glad my guide helped you and congrats on your skin! Keep it up, practise is the key in getting used to skinning.

 

You don't have to worry about the floating selection appearing when pasting the alpha texture back to the alpha channel btw, it will go there once you anker it. But you are free to use what suits you best.

 

Btw I never used Photoshop. The real Pros use Gimp :P

Edited by Stab/JG26_5tuka

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Thanks 5tuka.  The drag and drop of layers and channels, back and forth, is working great.

 

If I may be so bold as to suggest an addition of a sub-step to part of the procedure.

 

In the instructions, after the Alpha layer has been created, it mentions

 

 

First of all I noticed this grey creates too much shine for my taste so I darkened all parts of the airframe I want to be more matt. In this case it's wooden parts of the aircraft for example.
  (emphasis added)

 

I wasn't quite sure how you went about this darkening.  I assumed it was through the use of the normal tools.  Being lazy, I looked for a way to darken the Alpha layer across the board proportionately.  It is important however that the darker levels DO NOT go below 4 or they will become invisible.  What I did was duplicate the Alpha layer and work with that.  I then used the Colors - Curves menu.  I brought the upper right hand point down two blocks to darken the light grays and brought the line back in to the center for the lower left hand corner's last block to prevent over darkening of dark gray areas..  Here is an example of what my Adjust Color Curves looked like:

 

22714220730_9d3c0e858a_z.jpg

 

A word of caution: each template may be different, so you have to test the dark areas.

 

You can then use this Alpha layer as a base to adjust specific areas for additional brightening or darkening.  For me, since the templates already have lighter and darker areas in them for the various parts of the aircraft, I found just this adjustment to suit my needs for now.

 

Cheers!

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If you are reading this you want to know how to change the Alpha Channel to control the finish of an aircraft. 5tuka's steps above are excellent and allow for more detailed control of the finish of various parts of an aircraft than I am presenting here. I thought I would consolidate my methods which are spread out over a few posts and add a few things I have learned. My steps are more quick and dirty.

 

Some surfaces are meant to be more reflective than others, for example metal and wood. I find that generally these are already accounted for in the template's Alpha channel. Therefore all that is needed in most cases is a reduction of the lighter portions of the Alpha Channel proportionately across the boards to achieve satin and/or semi-matte finishes.

 

Using GIMP the following are the steps of adjusting the Alpha Channel that I use.

 

You will need to have the Layers open with the Channels tab also like this:

 

25333319472_3150e144e1.jpg

 

Go to the Channels tab. At the bottom of the Channels tab there is an Alpha1 channel. Drag this over to the image and drop it. This should turn the entire image gray. There is no need to deselect other channels.

 

This creates a new layer (not channel) in the Layers tab called Alpha1 Copy. It should be at the top of the Layers tab. You can deselect the visibility (eyeball) to see that nothing has changed in the other layers. I usually move this layer down to the Paint In Here section of the template but it probably doesn't matter.

 

Now make sure the Alpha1 Copy layer is selected and visible. From the menu go to Colors and click on Curves. You will see a box with a line going from the bottom left corner to the top right corner. The bottom of the box represents the darker portions of the image and the top the lighter portions.

 

Click and drag the upper right hand line down about 2 to 3 blocks. The further down the more matte the result. Then click the line one block over from the lower left and bring the line back up to one block. This preserves the darkest elements of the skin keeping them visible. Click OK to finish.

 

Here are images of the Curves screens.

 

25451724715_eef54896fc_c.jpg

 

24821182174_29c78a4370_c.jpg

 

25084145219_c1d85ca247_c.jpg

 

Now deselect the Alpha1 Copy visibility. Drag it to the Channels tab, placing it just above the Alpha1 channel at the bottom. (This is a copy and not a move.) Double check that the eyeball is deselected. You just created a new Alpha channel. Leave the original Alpha1 channel there, you may need it.

 

Now go ahead with the normal process for creating the skin dds. Make sure when you add the layer mask that it is the Aplha1 Copy that you adjusted. If you don't like the result, either tweak it in Layers and drag it to Channels tab again (or delete the channel and layer and do another, it's pretty quick).

 

For some reason GIMP would not allow me to follow the copy and paste steps laid out in 5tuka's instructions even though we had the same version, albeit different language. I found the drag and drop just by accident.

 

Just an aside. Although much of the VVS paint was “matte”, lacquer was applied in many instances to protect the paint and decrease drag. This of course would wear with time. So, although the default Alpha1 channel with its wet look is incorrect, IMHO a total matte plane may also be. I think the truth lies somewhere in between. If you still want a total matte aircraft, just don't add a layer mask at all.

 

I hope this is helpful.

 

Cheers!

Edited by 12.OIAE_Stick-95
  • Upvote 5

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I have a question about achieving a matte surface which neither approach above seems to answer.  Is there a way to change the alpha on a per layer basis?  For example, say you have adjusted the overall alpha and/or the individual plane parts to arrive at the gloss or matte surfaces you want for a summer skin.  Now you want to apply winter camo layer in matte.  On parts that are reflective (usually metal) the new winter camo would make them matte.  This will cut across plane parts, e.g., a metal wing may only be partly covered in winter camo so a portion would be matte and the rest remain more gloss.  How does one achieve this?  The only way I can think of is to duplicate the alpha you originally adjusted and reworking all the parts effected by the winter camo, thus having two alpha channels, one for summer, one for winter.  The prospect of having to readjust all the plane parts effected by the winter camo a second time seems laborious at best.

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I'd go ahead and create a new alpha channel from scratch. It allows you a maximum of customizeability and is very usefull as you can carry it on for different skins. It is however a good bunch of work to create and I don't know if my old tutorial is sufficient enought explaining that.

 

My plan is to make a video tutorial about that, but I can't promise since I've plenty of other projects going on atm.

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Thank you for these instructions. I practiced alpha channel editing with the Photoshop and everythnig works with it, too. Actually I don't flatten the image at last, I save it straight to .dds file from the layered PSD-file. It seems to work very good and the alpha layer mask is added there automatically when I tested the skin!

Edited by LLv32_Kanttori

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Can I make some repairs to the panel lines with the alpha channel? Or is there also so called "normal map" which is not matching with the new panel lines after editing?

I mean something like this:

bug09.jpg

Edited by LLv32_Kanttori

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Yes, there are normal maps but they're not availabel to us. We used to be able to extract and modify them but this has been changed a while back now.

 

It's possibel to add new panel lines via the alpha channel via visual tricks but it's difficult to "erease" some of the original ones.

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Yes, there are normal maps but they're not availabel to us. We used to be able to extract and modify them but this has been changed a while back now.

 

It's possibel to add new panel lines via the alpha channel via visual tricks but it's difficult to "erease" some of the original ones.

 

Thank you for that info 5stuka! Better not to touch the panel lines.

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Yes I've already tried making an early MiG-3 conversion by redrawing panel lines and deleting some things but the old panel lines and cowling latches can still be seen. I would definitely say to leave panel lines until we have access to normal maps.

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Awesome tutorial, it was really helpful!

 

The only part where I got confused was in the numerical scale for the whites.

 

You said 100 was matte, but did you mean glossy?

I understand matte as no or very little reflection, no shine.

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No, white value 100 means the painted surface will not reflect at all (like a skin without alpha channel).

 

Gloss increases the lower you go from 100 down to 50, after that it gets less. Vise versa for glow (diffuse light reflections).

 

To give you a guidline I'm usually using a 31-29 value grey for metal skin surfaces depending ob wethering state. That way the surface will still have some minor gloss when veiwed from extreme angles but also have a more eggshell type of look to it.

Edited by 6./ZG26_5tuka
  • Upvote 1

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Ok thanks for clarifying. I guess i need to experiment a bit more with the Alpha channel to get how it works.

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When I Cntl C the alpha layer back into the Channels tab, and hit Cntl V, it just places back into the top of my layers tab as a floating layer.

Edited by 71st_AH_Hooves

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When I Cntl C the alpha layer back into the Channels tab, and hit Cntl V, it just places back into the top of my layers tab as a floating layer.

Create a layer called "Alpha".

And anchor the floating layer. :salute:

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ow in GIMP to open for editing already made someone a skin ?

For this you need an extractor. :salute:

You must have used DxtBmp. Who is an extractor.

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For this you need an extractor. :salute:

You must have used DxtBmp. Who is an extractor.

Thank you
Is the GIMP itself unable to cope with this?
I need to open all layers for editing as it happens with the usual public template
Edited by Kraftowod

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Thank you
Is the GIMP itself unable to cope with this?

 

If you take a skin already made (.dds) and you open it with Gimp.

It will just give you the minimap layers.

399r.png
 
It is necessary to use an extractor to be able to modify it in bmp. To put it simply, it will give you a bmp image of the skins.
y4yf.jpg
 
I made it simple to show you if you want to contact me by MP.

I would tell you how to do for each step in detail.

 
I hope that one speaks well of this?

If you talk about the alpha channel this has nothing to do

.
 
 
 
 
 
Edited by A-E-Hartmann

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On 3/22/2015 at 12:47 PM, 6./ZG26_5tuka said:

Visual demonstration of the effects:

 

Note: In this demo I used geys with value of 100 for the fin, 75 for the right wing, 50 for the fuselage, 25 for the left wings and 0 for the left stabilizer.

 

Notice how even though the alpha(specular) channel has been altered there is still a noticeable difference in shine between the wooden and metal part of the wing? This is because the game is pulling the alpha channel from planename_d.dds for the gloss of the surface.

 

The blue channel of the bumpmap is being used for ambient lighting/reflection inheritance and if you are trying to change the bump effect then you should only be changing the red and green channels.

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Thank you so much this tutorial really helped me. Altho i still have one question. Since English is not my first language and the translator doesen't really help either can anyone explain in simple therms the difference between Shine and Glow?

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I will try to explain it in more clear terms (to be fair the guide is quite dated and I'm not a native speaker myself).

 

If you use high value / RGB the reflections will be stronger, glossier, 'mirror like'. This is what I originally referred to as 'shine'.

Lower value / RGB will give you diffuse reflections, matt finishes, which is what I called 'glow'.

 

If you are unsure about the effects you can take a look at the official Alpha Channel textures to see the difference between the grey tones. It is very much self explanatory.

 

 

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