Celestia Forums

I need a little help with something. I have found a nice cloud map for earth that I would like to use in Celestia that is in JPG format. When I try to convert it in Photoshop (I have version 6) it seems that the “graduated” transparency is not supported, sections of the picture are either transparent or completely opaque.

I tried converting the picture to grayscale and putting it in the alpha channel of the picture then using the “select layer transparency” option, but that still does not seem to work properly. Is there another program I should use for transparent PNG files?

I have never been able to actually make a cloudmap from scratch in Photoshop. I always use THE GIMP to make the initial transparent cloudmap and then move it to Photoshop for editing. Be forewarned that only a maximum cloudmap of 4096x2048 can be used in Celestia at this time. If you make one from lets say Blue-Marbles 8k cloudmap Celestia will just size it down to either 4k or 2k depending on witch resolution your video card can support. You other option is that I could put the cloudmap together for you and then you could tweak it till your hearts content.

Don.

P.S.
I can make your cloudmap in probably 2 minutes and have it back to you quite fast.

Dunno if this will help much, but what I did to make cloudmaps before was:

Open your image in photoshop
Use background eraser with a setting of about 60%, and discontigous sampling.
Go over the whole image with a big brush (300 or so)
Give it a slight blueish tint- to get rid of any greyness at the edge of the clouds
save as normal png

That works well for the clouds from blue marble, but may not for textures from other places... Just thought i'd give my 2 euro cents

Hi snabald,

There are several ways in Photoshop to build a cloud map with PNG-format. Simple sayed you must create an picture with transparency. This can be done with a selection and delete transparent areas or a selection with an empty (transparent) layer and the fill tool or a layer-mask with normal or single color layer. Before I come to the details now I have only a german Photoshop and so i don't know the correct english terms.
First check if the tool-window and the layer-window is open (can be done in the window-menu). The layer/channel-window is very important.
Now open your grey cloud file (I expect it's grey). In the layer-window appears a 'background'-layer with a tumbnail of the clouds. Doublelclick this tumbnail and press OK in the next window. This changes the background to a real layer. Now you should check if the mode is greyscale (menue: picture/mode/greyscale). If not change to this mode. This point is a general start of most Photoshop jobs (change to real layer and check/set the picture mode).

Now the next steps can be very different. I will explain only an simple way for a very simple cloud map.
Goto menue:selection/load selection. A little window appear where you can press normally OK (check if in the channel box 'background greyscale' is selected). A blinking selection should appear. Now create a new layer (click the second right button below in the layer-window or press 'CRTL + SHIFT + N' ). Then set the foregroud color to white (if you want white clouds). Choose the fill tool (this is a little paint bucket). Check if opaque and tolerance is 100% and no of the checkboxes is set. Then click on the picture and the selection should be filled. Now press 'CTRL + D' to remove the selection. Finally delete the old layer by pressing the 'dustbin'-button in the layer-window and save the picture as PNG.

Finally some general things about Photoshop:

A selection is like a mask a 8 bit grey scaled picture but we can see only the 50% level. You can save a selection to a layer mask. A selection can be built from an alpha channel or from a greyscaled layer. If you want use an certain (color) channel for a masc duplicate this by right-clicking in the channel-window and build an alpha-channel.

It's possible to copy a grey scaled picture direct in a mask or a color channel. But this works only in the channel-window. Select the source channel with 'CTRL + A' copy it with 'CTRL + C' to clipboard. Then select the layer where the mask should saved and create if necessary a new new mask. Switch to channel-window and select there the mask-channel and make it visible. Now past in with 'CTRL + V' the picture. Before switching to the layer-window remove the mask from visibility.

I hope this helps a bit.

Bye Jens