Beware of Transparent Pixels
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Beware of Transparent Pixels
1–10 of 97 posts
Re: Beware of Transparent Pixels
#2> pay attention to what color you put inside the transparent pixels
I don't understand this. When I make transparency I don't use any color? I use the Eraser tool or Ctrl-X, not a color with 0 opacity.
Re: Beware of Transparent Pixels
#3> pay attention to what color you put inside the transparent pixels I don't understand this. When I make transparency I don't use any color? I use the Eraser tool or Ctrl-X, not a color with 0 opacity.
"And be careful to export the RGB values of transparent pixels when you save to PNG for example, many programs will by default discard transparent pixel RGB data and replace it with a solid color (white or black) during the export to help with the compression."
Here is some information for Photoshop and a plugin you can use:
https://graphicdesign.stackexchange.com/questions/63783/how-...
Re: Beware of Transparent Pixels
#4s/sawn/swan/
Re: Beware of Transparent Pixels
#5> pay attention to what color you put inside the transparent pixels I don't understand this. When I make transparency I don't use any color? I use the Eraser tool or Ctrl-X, not a color with 0 opacity.
Regardless of how you perceive making it, the representation is still (nearly always) a color underneath an alpha channel.
If you inspect the image in a full-featured editor like Photoshop or GIMP, you can inspect the channels individually or remove the transparency entirely to see this fact.
I think with most GUI programs, the eraser and cut tool will leave color as what it was before it became transparent.
EDIT: saurik has a good point that I forgot about -- many editors may actually throw the colors away when you export unless you ask them not to.
Re: Beware of Transparent Pixels
#6> pay attention to what color you put inside the transparent pixels I don't understand this. When I make transparency I don't use any color? I use the Eraser tool or Ctrl-X, not a color with 0 opacity.
Each pixel is defined by 32 bits -- 8 R, 8 B, 8 G, 8 A. Even if alpha is 0, there has to be information stored in Red, Green, Blue. There can't be "no information", because then a pixel is not defined by 32 bits of information. There is always a "color" (RGB values) for transparent pixels. Some editors will set the RGB values to 0 or 255 when fully-transparent pixels are saved/output. Others don't.
As the author mentions, certain resampling algorithms might be naive or plain ignorant about how to resample images with potentially transparent pixels. Should transparent pixels not count to the final pixel? Should all pixels be averaged? Should the output pixel be the median or mode value? If the image is being resampled to 1/3 its size the resampling can be very cheap if only the middle of the 3x3 pixel cluster is selected as the output value.
Re: Beware of Transparent Pixels
#7> pay attention to what color you put inside the transparent pixels I don't understand this. When I make transparency I don't use any color? I use the Eraser tool or Ctrl-X, not a color with 0 opacity.
This is actually a very common problem with 3-D stuff and transparency in textures. This isn't an issue with the colors of the pixels themselves, it's an issue with texture filtering. nVidia has a pretty good explanation as it applies to games and 3d graphics: https://developer.nvidia.com/content/alpha-blending-pre-or-n...
Say you have two adjacent pixels using floating point RGBA values of (0,0,0,0) and (1,1,1,1), and you apply it to a 3-d shape. Because of the rasterization algorithm, you will be sampling weighted averages of the two pixels, either because you're scaling up and need to interpolate, or because you're scaling down and need to average.
The average of (0,0,0,0) (fully transparent) and (1,1,1,1) (opaque white) is (0.5,0.5,0.5,0.5), a half transparent gray. But you'd intuitively expect (1,1,1,0.5), half transparent white. This is the essence of the problem. The fix is to make sure that your transparent pixel was (1,1,1,0) and not (0,0,0,0).
Re: Beware of Transparent Pixels
#8Reminds me of "Is there a reason Hillary Clinton's logo has hidden notches?"
https://graphicdesign.stackexchange.com/questions/73601/is-t...
Re: Beware of Transparent Pixels
#9> Even with an alpha of 0, a pixel still has some RGB color value associated with it.
Wish the article was more clear as to why this happens. Let me elucidate: this happens because, per the PNG standard[0], 0-alpha pixels have their color technically undefined. This means that image editors can use these values (e.g. XX XX XX 00) for whatever -- generally some way of optimizing, or, more often than not, just garbage. There are ways to get around this by using an actual alpha channel in Photoshop[1], or by using certain flags in imagemagick[2].
[0] https://www.w3.org/TR/PNG/
[1] https://feedback.photoshop.com/photoshop_family/topics/png-t...
[2] http://www.imagemagick.org/discourse-server/viewtopic.php?t=...
Re: Beware of Transparent Pixels
#10Using premultiplied alpha avoids this. Jim Blinn's books from the 90s give a very thoughtful treatment of the topic.