Alpha Color

[Mike]

I'm an amateur when it comes to graphic art, I did photoshoping years back, but I never try color manipulation (beside burn and opacity -> is that even coloring?). : p

So yea, I have this picture with white background, and I've browsed a bit using google that alpha can be used to make the white background to be transparent, but when I browsed about alpha value and manipulation alpha, I was sent to pages of math formulas, haha. And I tried looking at the photoshop, but I can't find alpha color. I found rgb and black though. Sorry, that I've been asking questions a lot lately, I just want to build a nice game for free. : x

So yea, what should I use as value for alpha to make the white background to be transparent? What if the alpha background is black? What if it's purple? And yes, they are solid colors (solid white, solid black, and so on).

 

[Kes]

I use GIMP, so the exact instructions will vary, but in the Layers command, I select Transparency, then Add alpha channel.  Then I can simply select the background with a tool which might be called a Magic Wand in Photoshop and simply delete it, leaving it transparent around the main image.  I would imagine that it is something like that in Photoshop.

 

[Andar]

if the white is a unicolor white, you might want to save the picture as BMP and then add it by the resource manager. That way the resource manager can create the alpha channel transparencies for you (don't save it in a format that already has an alpha channel, as the resource manager will then assume that the transparancy already exists).


However, that will usually make the picture larger compared to directly creating the alpha data in a program like photoshop.


With photoshop, you create a new file with transparent background, copy the image data into that and then use magic selection and delete to remove the solid color parts before saving in a format that allows for transparency (PNG is what is used in RM)

 

[Tsukihime]

Alpha is not a color. That is why you are getting math.


If you are looking for a solid color that would be safe to use as a transparency mask, you should pick a color that the sprite does not have. You can use different colors for different sprites; as long as RM doesn't have to work hard to figure out whether one pixel should be rendered or not.

 

[Mike]

Thanks for the inputs. : )

I use GIMP, so the exact instructions will vary, but in the Layers command, I select Transparency, then Add alpha channel.  Then I can simply select the background with a tool which might be called a Magic Wand in Photoshop and simply delete it, leaving it transparent around the main image.  I would imagine that it is something like that in Photoshop.

Does GIMP support multi-files manipulation? For example: I have 200 small pictures with the same alpha type, do I need to go to each picture and manually do the transparency thingy? Or is there a function where I could just open all files and manipulate them altogether like some kind of synchronization.

if the white is a unicolor white, you might want to save the picture as BMP and then add it by the resource manager. That way the resource manager can create the alpha channel transparencies for you (don't save it in a format that already has an alpha channel, as the resource manager will then assume that the transparancy already exists).

However, that will usually make the picture larger compared to directly creating the alpha data in a program like photoshop.
With photoshop, you create a new file with transparent background, copy the image data into that and then use magic selection and delete to remove the solid color parts before saving in a format that allows for transparency (PNG is what is used in RM) 

Hum, I dealing with hundreds of pictures (similar names happen) and sub-folders, so going to the resource manager might not end well for me. : p

And yea, I've done transparent works more before with the lasso / wand, but doing so hundreds of time is discouraging. xD

Alpha is not a color. That is why you are getting math.
If you are looking for a solid color that would be safe to use as a transparency mask, you should pick a color that the sprite does not have. You can use different colors for different sprites; as long as RM doesn't have to work hard to figure out whether one pixel should be rendered or not.

Oh, how do you do that transparency mask?

 

[Tsukihime]

It doesn't need to be explicitly an alpha channel.


You can just flood fill all the transparent parts with a particular color.


If you're using a modern image editor that supports alphas, you can even just delete all the pixels and it will automatically be saved with the correct transparencies assuming your format supports it (eg: 32bpp PNG)


If you need to do batch image processing you should look into imagemagick.

 

[Kes]

Does GIMP support multi-files manipulation? For example: I have 200 small pictures with the same alpha type, do I need to go to each picture and manually do the transparency thingy? Or is there a function where I could just open all files and manipulate them altogether like some kind of synchronization.

Truthful answer is I've never tried, but I don't think so.  But maybe some GIMP wizard will drop by and say, "Of course there is.  You just....

 

[Mike]

If you need to do batch image processing you should look into imagemagick. 

Thank you so much, my life is complete.

 

[Andar]

Another tool usefull for image batch processing and image management is ThumbsPlus.


Thumbsplus is the cheapest image viewer I know of that also supports content analysis of pictures - most other image management programs, when asked to find duplicates, look at filenames only - ThumbsPlus analyses the picture content instead, and you can set the filters to find false-colored variants of the same pictures with different names and things like that.

 

[Engr. Adiktuzmiko]

you can also just use like Paint.net, use magic wand to select the white background or whatever color you wanna "erase", press delete... save as .PNG... on the file browser of windows, it will probably look like it has a white background but programs that will use it will already know that it is in face transparent