An At Sea Landscape would be great.
You seem to have CSS turned off.
Please don't fill out this field.
I'm trying to build a new landscape that is a seascape. I plan on going out on
the boat this weekend and taking a series of digital photos.
The problem I have is finding and using an image editor to create
transparency. I thought the best tool would be GraphicConverter. I decide a
first step to learn how to do this would be to take an existing Stellarium
landscape and expand the transparent area. I try and try to do this but I just
can't seem to "open up the canopy" on trees_512.png. I can "erase" / "blank"
many of the overhanging tree limbs and when I use the transparency tool the
new area looks transparent to GraphicConverter. In fact when I save the
modified file to my desktop the transparent "hole" in the file icon is definitely
larger but Stellarium still thinks the new transparent area is still occluded.
The newly erased branches are there but they are white in Stellarium daytime.
And only the same old area of the sky comes through at "night".
As you can tell Iâ€™m not imaging expert. Could you guide me? I can send you a
modified image if you like.
Mac OS X 10.3.9
Forgive me if I'm mistaken, but it sounds like you are using the eraser tool in GraphicsConverter rather than editing the alpha mask.
In most programs when you erase an area of an image then save it to a non-native format it will fill/blend the transparent areas you've erased with a background color. Unless the alpha mask was edited the alpha transparency of the image will remain unchanged and you'll see areas that will now appear to be painted a single color in alpha channel-aware applications.
I haven't used GraphicsConverter before, so I don't know if that program can load, edit and save an alpha mask. But what you need to look for is a grayscale image stored in the alpha channel.
A typical alpha mask in one of the Guereins textures will appear to have a black sky and white ground and trees, with various shades of gray pixels where the two colors meet. If you don't see anything like this in GraphicsConverter you aren't seeing the alpha mask.
To make an area completely transparent you paint that part of the alpha mask black. To make an area opaque you paint it white. To make an area partially transparent you paint it gray. The darker the gray the more transparent it will be. The lighter the gray the more opaque it will be.
I hope this explanation begins to help you understand what to look for. Alpha masks are very easy to understand once you become familiar with them.
I have kind of stumbled into solving this (I think I hope). You can view the alpha channel with GC and it is white=transparent and black=opaque (opposite of what you suggest). The thing I figured out after some trial and error is that you cannot use the transparency tool but you need to use the eraser on the alpha channel. The funky thing is that the eraser does the opposite of erase! You need to set the eraser to white (this is not obvious until you stumble onto it).
Again the key is to view the alpha channel and "paint" white pixels over the black ones. The less black alpha channel pixels you have the larger the area of transparency.
The software does have some redraw problems in that after you work on the alpha channel the program tends to miss-draw the image leaving "pixel dust" where you move any tool (well any tool I used). Just save it, and re-open.
I think it would be an improvement to the software if you could virtually merge the alpha mask with the image front. This way you could easily see what you are erasing. Right now it takes trial and error to get the erased area of the image and the erased area of the alpha channel to match.
I'll send this to the company to see what they say. I like the tool in most respects.
BTW, GIMP has the feature of erasing the alpha pixels at the same time you are erasing the image.
In an alpha mask black is transparent, white is opaque and grays are translucent. For PNG there's no other way it's done.
(BTW, in my previous post I used the word transparent when translucent should have been used.)
If your application allows you to view the alpha mask you'll see it's as I describe. For the work I did this evening I simply painted directly onto the mask (using Paint Shop Pro).
You wrote "In an alpha mask black is transparent, white is opaque and grays are translucent. For PNG there's no other way it's done"
Wrong. Wrong, Wrong. Absolutely positively defnitely NOT. In GC the black "mask" is opaque and the white is transparent. THERE IS NO DOUBT ABOUT IT. NONE, ZIP, NADA. Try it.
If you don't want to accept an explanation from an experienced user who has actally made Stellarium landscapes with alpha masks then research it yourself. Try doing a Google search using the keywords:
make alpha mask
(Be sure to also view the image search results.)
Experience or not. Web sites references or not. Expertise or not. GOOG on anything you like. But if you want to INCREASE transparency with GC you need to INCREASE the white and DECREASE the black when viewing the alpha channel mask. As I said it is not intuitive. But it is what it is. Until you figure this out, and the trick on how to do it, you will not get the desired results.
I've posted two links in this thread to landscape I've made, both with alpha masks. Why don't you download them and try them yourself in Stellarium? Then you can lecture me on if I know what I'm doing.
Give it up DUDE. Check with Thorsten Lemke the maker of GC he will tell you EXACTLY what I said. The black pixels on the alpha channel are opaque. JUST TRY IT. All your theory, expertize are useless and you will cause people to not get landscapes to work if they follow your advice using GC.
Trust me people. This guy is NOT listening. If you have the really nice GC program you need to show the alpha/mask and set the pixels white to get transparency.
Hey Macinflorida, give it up! We don't care whether it's black or white or anything else! You don"t have to get nervous nor to SHOUT about this pointless cause.
Instead, use your energy to make some nice landscape for stellarium :)
This is the really funny thing about the internet. You get some so called self-describe expert using some citation or their personal experience to create dogma.
simple set the background color (after show alpha channel) to white.
I did this, erased a ton of BLACK pixels on the alpha/mask channel (increased the white area) and I got a larger transparent area!!!
Keep it civil, macinflorida. We were only trying to help you by describing some conventions concerning alpha transparency, as we're not using GraphicConverter. Nothing to get riled up about.
So, aside from obvious interface differences between graphic editing software, this is a problem solved?
Please consider sharing the landscape, if you think it's worth it.
Thanks, anonymous helper!
the transparent part is white.
Not riled, Amused. The funny thing about the web is that if it was around in the early 1800s I could use it anonymously today to prove that we are at war with England and that New Orleans is saved. People giving advice on using a tool should use it and no matter how much THEORY they have they should listen to those that got a tool to work.
Strongly recommend Thorstens tool BTW for managing images for Stellarium. As soon as it warms up (today it is freezing 60F) I'll go out and get some seascapes in the gulf of mexico. Just remember when using to edit masks in GC black is OPAQUE. It helps :) hehe
Here are specific references to GraphicConverter and alpha masks:
Maybe there is some information there you can learn from. I've done my best to try to help you.
I'll try to close my comments in this thread as graciously as possible...
If GraphicConverter uses a non-standard convention for displaying and editing the alpha channel then you should defer to the advice of macinflorida.
But please also remember that this is not typical of most applications.
Next issue: Today is the 22nd and I'll be removing Ocean.zip from my site soon. Please get it now if you want it:
Please feel free to do with it what you like. It's yours (public domain). ;)
You can download a not very good ocean landscape I quickly made using Terragen here:
There are installation instructions included in the ZIP archive.
This ZIP file will only be available until December 21, 2005. After then I ask anyone who has downloaded a copy to make it available to anyone who requests it.
Hey, that's simple and it looks good!
Can you give us some pointers for generating landscapes that can be used in Stellarium with Terragen? Does it render the side textures and the separate ground texture in one go?
If I understand your your last question the answer is yes and no. :) You can make a script for Terragen that will output six individual images that can be used as a cubic panorama (skybox). Here is some useful information on that:
Unfortunately Stellarium doesn't use cubic panoramas (things would be so much easier if it did). It has to be converted to a more appropriate form. I start by first making a cubic cross from the six Terragen images, like the one depicted here:
I use my paint program with grids turned on to do this. If each Terragen image is 1024 x 1024 set your grid to that spacing. The placement of each image should be as follows:
Up - top of cross
West - left side of cross
North - center of cross
East - right side of cross
Down - under center
South - bottom of cross and rotated 180°
Then I use the free HDR Shop v1 to convert it from cubic cross to latitude/longitude using panoramic transformation. Here's where you can download the program:
Be sure the output width is four times the width of the original cube side. In other words, if each of the Terragen images were 1024 pixels wide then set the output width to 4096 pixels. The output height should be half the output width.
Save the transformed image and open it in your paint program. Crop off the top 50% of the image. Using the example dimension you should now have an image that is 4096 x 1024. Next, crop off the bottom 50% so that the image is now 4096 x 512. Divide the image into eight equal squares of 512 x 512 each.
At this point I added an alpha mask with a transparent area one pixel high across the top of each image. This made a big difference in how the horizon was rendered in Stellarium.
Depending on how capable your graphics card is you may want to resize each square to 256 x 256 or leave them at 512 x 512. Either way, save all eight images as PNG.
The final step is to get the original Terragen "down" image. This will be the "down" texture in Stellarium. Keep it twice the dimensions of the sides or else it will appear much more pixelated than the rest of the panorama. You should now have a new landscape to add to the Stellarium landscapes.ini file. :D
One thing I should mention - this technique only works for landscapes where nothing appears above the horizon. The cropping and dividing steps will be different for your more typical terrestrial scenery.
Thanks for your good advices, I just realize that adding cubic panoramas rendering to stellarium should not be very difficult. Only a new Landscape derived class need to be added. This would take less than 1 hour for a skilled programmer.
Could you make an example of cubic panorama textures to help developer try its integration?
I just sent you an e-mail with a link to the cubic panorama. :)
D'oh! Perhaps other developers may want access to this, too. Here's the download link:
I'll keep it available for several days.
I have a cubic panorama I made at Big Meadows in Shenandoah National Park. I'll send it to you as soon as the alpha mask is done. Perhaps as soon as tomorrow.
If it's possible it might be useful to support rendering all sides of the cube in Stellarium, including the overhead texture. With an alpha mask it opens up some possibilities.