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+--- Thread: Checkerboard.. why? (/Thread-Checkerboard-why)
Checkerboard.. why? - RustyBolt - 04-05-2022
I loaded an RGB image which I added an Alpha channel to and then decomposed it. I pasted another image into the alpha channel and then did a compose into an RGBA image. At this point the image it shows me on the screen now has a checkerboard pattern on it even though none of the channels had any transparent areas. I saved the image as a png. If I open it with a different program it appears normal. If I open it with Gimp, it as the checkerboard pattern on it.
I am new to Gimp, so I would lke to know what this is indicating and how to remove it?
RE: Checkerboard.. why? - rich2005 - 04-05-2022
The checker pattern indicates transparency.
Your work-flow is a bit strange but anything you paste into the decomposed alpha = various degrees of opacity The alpha channel is a mask where Black = transparent, White = opaque, Anything in between = degrees of semi-transparent.
Some image viewers will show transparency (usually as a checker pattern) but some do not.
You can get the same effect if you add a layer mask (white) Layer > Mask > Add layer mask to the first image and paste the second image into that.
Want to lose the pattern ? Get rid of the alpha channel Layer > Transparency > Remove Alpha Channel .
Need the alpha channel but not the pattern, It can be set to white in Edit > Preferences > Interface > Display then the Transparency Check style drop down menu
RE: Checkerboard.. why? - RustyBolt - 04-05-2022
(04-05-2022, 02:27 PM)rich2005 Wrote: The checker pattern indicates transparency.
Your work-flow is a bit strange but anything you paste into the decomposed alpha = various degrees of opacity The alpha channel is a mask where Black = transparent, White = opaque, Anything in between = degrees of semi-transparent.
Some image viewers will show transparency (usually as a checker pattern) but some do not.
You can get the same effect if you add a layer mask (white) Layer > Mask > Add layer mask to the first image and paste the second image into that.
Want to lose the pattern ? Get rid of the alpha channel Layer > Transparency > Remove Alpha Channel .
Need the alpha channel but not the pattern, It can be set to white in Edit > Preferences > Interface > Display then the Transparency Check style drop down menu
My workflow might be strange because today is the first day that I have used Gimp and the workflow came about through trial and error. What I am trying to do is as follows:
I have an image and I have a roughness mask as a seperate image. So I want to add an alpha channel to the image so that I can paste the roughness mask into the image. Then when I load this into a game engine it only needs to read from one image instead of two. I tried Googling this but the answers I found either made no sense or they did not work.
RE: Checkerboard.. why? - rich2005 - 04-05-2022
(04-05-2022, 03:10 PM)RustyBolt Wrote: My workflow might be strange because today is the first day that I have used Gimp and the workflow came about through trial and error. What I am trying to do is as follows:
I have an image and I have a roughness mask as a seperate image. So I want to add an alpha channel to the image so that I can paste the roughness mask into the image. Then when I load this into a game engine it only needs to read from one image instead of two. I tried Googling this but the answers I found either made no sense or they did not work.
Sorry if I can not give a helpful answer but I am not into games and their image formats. It looks like your game engine uses an alpha chanel for a purpose it was not intended for, uses it as a bump or displacement mask.
I have seen questions like this before, often it is something from a Photoshop procedure. If your game engine needs an alpha channel, then you have to keep it. If the pattern bothers you when working in Gimp put a temporary white layer bottom of the layer stack and remove it before you export.
Then it is try-and-see in your game engine.
I guess something like this: http://wiki.polycount.com/wiki/ChannelPacking
RE: Checkerboard.. why? - RustyBolt - 04-05-2022
Hi. Its not a case that it uses the alpha. Its just a way of packing as many texture masks into a single image. This reduces the number of texture reads the engine needs to do. So RGB with alpha allows for 4 masks per texture which is a lot better than reading 4 separate images for 4 masks
RE: Checkerboard.. why? - rich2005 - 04-05-2022
As before, I have seen this 'use alpha -channel' before in connection with computer games. To go back to your original question
Quote:At this point the image it shows me on the screen now has a checkerboard pattern on it even though none of the channels had any transparent areas.
As soon as you add an alpha channel and paint in it, some areas will display transparency, that is the way it works
Quote:I saved the image as a png. If I open it with a different program it appears normal. If I open it with Gimp, it as the checkerboard pattern on it.
What is normal ? That is the way Gimp displays transparency that is normal. Look at previous post on how Gimp displays it.
Different viewers might / might not display alpha. I use a light pattern in Gimp. All the same image, one viewer shows checks, the other not. AFAIK not going to make any difference in your game.
[attachment=7739]
RE: Checkerboard.. why? - RustyBolt - 04-06-2022
Yes but why over the whole image?
RE: Checkerboard.. why? - rich2005 - 04-06-2022
Quote:Yes but why over the whole image?
Because that is the image / layer size and your pasted in alpha channel has lots of semi-transparency.
This is a dark to light gradient in the alpha channel, no 100% black for fully transparent, no 100% white for full opacity just semi-transparency all over.
[attachment=7741]
Going back to your dislike of the checker pattern, change it to either white / black / grey in Gimp preferences.
Same image, black representation of transparency.
[attachment=7742]
RE: Checkerboard.. why? - RustyBolt - 04-06-2022
Thank you very much for all your help