A million dollar question (Part 1)

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

OK, this is a long story...

I have these images here rendered in 3ds max - one is PNG (no alpha), the other one is TAGRA (.tga) as a Z-depth map.

Sorry, tagra isn't acceptable on GC, what you see is jpg image, so i'm attaching .tga

Attachment:

File comment: Zipped TAGRA depth map

Zdepth_map_TGA.zip [232.27 KiB]
Downloaded 169 times

The question is: how can one make tagra image* an alpha channel of the PNG image in GIMP
(in other words, to make a depth map an alpha channel of PNG image)?

I seem to have tried all possible ways to do so but not sure gimp is capable of doing it.

What I add as a new channel in GIMP does affect RGB channels, and that is not supposed to happen (as an argument I can refer to the same procedure in Photoshop).

One can suggest to add tga image as a layer mask but it would not do the trick (I will explain later but for now it's better off to keep it undisclosed - might be part 2 of the million dollar question)

Thanks.

P.S. I have obviously managed to add .tga file as a channel playing with the opasity values in gimp but it
is not a true alpha channel as it affects the original image in a destructive way.

P.P.S. *tagra or jpg format - isn't really important in this case.

Ronounours · **Joined:** Jan 03, 2011 **Posts:** 1656

Not sure how to do this with GIMP, I used the CLI version of G'MIC to do it.
See attached file.

Attachment:

2205.png [ 1.63 MiB | Viewed 4005 times ]

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Thanks, David. What you refer to CLI is the command line operation, right?
Well, as I can see the resulting image is also affected (inversive to what i've got in GIMP).
The thing is, PS adds the tagra depth map as an alpha channel without affecting the original
image.
What the alpha depth is needed for is the possibility to create cameras variable DOF effect
like this one.

Odinbc · **Posted:** Mon Jul 15, 2013 1:55 pm **(#4)**

XnView reads and writes Targa files, check its image menu for possible options.

Lurifax73 · **Posted:** Mon Jul 15, 2013 1:55 pm **(#5)**

This rocks I made few year ago on Blender 2.5 Interial.

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Odinbc wrote:

XnView reads and writes Targa files, check its image menu for possible options.

GIMP supports tga files without any problem, that's not what's in question here, Odin.

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

It's good, Lurifax, the question is about GIMP, not Blender or any other 3d app.
I'll come back later with more pictures of what i'm trying to resolve here.
Sorry, if i didn't make it very clear from the start, but it seems confusing for many to get what i'm after.

saulgoode · **Posted:** Mon Jul 15, 2013 2:29 pm **(#8)**

* Open PNG image
* Open As Layers TGA image
* Edit->Cut
* Layer->Mask->Add Layer Mask
* Edit->Paste
* Layer->Anchor Layer
* Layer->Mask->Apply Layer Mask

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Thanks, sg!
I had no problem with creating a layer mask. That was the first thing i tried.

Here

K1TesseraEna wrote:

One can suggest to add tga image as a layer mask but it would not do the trick (I will explain later but for now it's better off to keep it undisclosed - might be part 2 of the million dollar question)

ofnuts · **Joined:** Oct 25, 2010 **Posts:** 4757

saulgoode wrote:

* Open PNG image
* Open As Layers TGA image
* Edit->Cut
* Layer->Mask->Add Layer Mask
* Edit->Paste
* Layer->Anchor Layer
* Layer->Mask->Apply Layer Mask

Slightly simpler solution:
* Open As Layers TGA image
* In Channels drag any of the RGB channels to make a copy
* Layer->Mask->Add Layer Mask, use the copied channel
* Layer->Mask->Apply Layer Mask

PhotoComix · **Joined:** Apr 12, 2010 **Posts:** 5870

K1TesseraEna wrote:

[font=Tahoma]
Well, as I can see the resulting image is also affected (inversive to what i've got in GIMP).
The thing is, PS adds the tagra depth map as an alpha channel without affecting the original
image.
What the alpha depth is needed for is the possibility to create cameras variable DOF effect
like this one.

Maybe the image is not affected as may seems:
just place a black (or dark grey) layer behind, and should again look identical

As you know the alpha channel is NORMALLY used for transparency, and change in the transparency will always change the look
(except if you correct adding a layer behind )

BUT in your case the alpha channel will be used to store a depthmap , not to calculate transparency so should be no problems

--------------------------------------

In case you don't find another solution should be trivial wrote a little gmic filter to do it

But again if is read as was the "alpha" of RGBA, for sure the Z-buffer will modify the image
THE POINT is the alpha will be read as a depthmap for DOF , and not as normally used, to calculate transparency

lylejk · **Joined:** Sep 24, 2010 **Posts:** 12535

Apologize K1Te; couldn't help myself (yes; a stereogram).

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

LOL. Thanks, Lyle! Been playing myself with some depth maps I've made in
Blender and 3ds max. Using Stereogram Maker. What program are you on?

lylejk · **Joined:** Sep 24, 2010 **Posts:** 12535

GIMP's magiceye plugin.

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

OK now, this is what i actually need.

To create depth of field effect in image rendered with 3D application.
Here's the workflow:
Render image in Blender (image #1 in OP, PNG)
Render depth map (image #2, TGA)
Both steps could be done with Blender, 3ds max, Cinema4d, etc.

Open both files in PS and add depth map as an alpha channel to PNG.

Using PS Lens Blur filter and alpha channel as a Depth Map, change 'in focus' depth by sliding Blur Focal Distance controller.

I've made APNG animation out of the image sequence to demonstrate how the depth map works.
This technique is being used to create videoFX from a single shot.
In After Effects it could be done in one go just using single image with zdepth alpha channel.

Creating amateur DOF effect in GIMP could be done by duplicating bg layer, blurring it, adding layer mask and
applying b/w gradient to that mask. This may actually work for the images without objects obliterating each
other along Z axis (depth). But in most cases it looks creepy.

Obviously, GIMP does not have the default Lens Blur plugin. 3rd party Focus Blur seems to be a
plugin of choice here but that's Part 2 of the million dollar question

`

PhotoComix · **Joined:** Apr 12, 2010 **Posts:** 5870

Not sure for Gimp but that should be be possible with Gmic

One of the Gmic filter contributors ,Tom Keil did already some cool filters for 3d effects and animations may be interested

I don't think he follows gimpchat but if you post a request on the gmic group on flickr he will see

EDIT
i am not speaking of the Focus blur, but of the all the process you describe

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

PhotoComix wrote:

Not sure for Gimp but that should be be possible with Gmic

One of the Gmic filter contributors ,Tom Keil did already some cool filters for 3d effects and animations may be interested

I don't think he follows gimpchat but if you post a request on the gmic group on flickr he will see

EDIT
i am not speaking of the Focus blur, but of the all the process you describe

Thanks, PC! I'm at my sister's now (means no GIMP,)
using her access to Adobe CC, but will check out GMIC as soon as i get home.

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Ronounours wrote:

Not sure how to do this with GIMP, I used the CLI version of G'MIC to do it.
See attached file.

Attachment:

2205.png

Hey, David! I like the 'fog' effect in your image!
Could be a cool idea for a GMIC mist/fog filter using depth map, don't you think?

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

here's slightly improved apng animation

Rod · **Joined:** May 16, 2010 **Posts:** 14715 **Location:** USA

That is a really neat effect.

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