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Author Topic: getting pixels from sf::Image  (Read 1972 times)

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treez

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getting pixels from sf::Image
« on: February 10, 2016, 12:28:16 am »
I am currently trying to change the values of pixels of an Image.

When I change r g b values of an image and then I save it to a file it works propery.

Then I tried to change the alpha value also (I assing 253 or 245) and save the image. And my program does save it.

And then one weird thing happens when I open that changed image. The r g and b values are changed the way I changed them before, but alpha is ALWAYS 255 and I am wondering why if I saved the image.

As you might know, I am using setPixel function to change the pixels.
« Last Edit: February 10, 2016, 12:31:07 am by treez »

eXpl0it3r

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Re: getting pixels from sf::Image
« Reply #1 on: February 10, 2016, 01:57:03 am »
Do you save it in a format that supports transparency (e.g. PNG)?
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treez

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Re: getting pixels from sf::Image
« Reply #2 on: February 10, 2016, 03:08:15 pm »
I was using .bmp format. I checked if it supports transparency and Google says it does.


EDIT: well.. I ended up checking all the types of images that SFML supports and the format that works is indeed .png.

Still not sure why the others arent working, guess Google is a liar or SFML has some buggs.
« Last Edit: February 10, 2016, 10:09:18 pm by treez »

eXpl0it3r

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getting pixels from sf::Image
« Reply #3 on: February 11, 2016, 02:56:50 am »
We use stb_image to load images. It says that it doesn't support 1 bpp und RLE BMP files, nothing so far against transparent BMP though.

But again, BMP is a "bad" format, as such you should stick to PNG.
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Mario

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Re: getting pixels from sf::Image
« Reply #4 on: February 11, 2016, 04:02:17 pm »
The standard Windows Bitmap format does not support any transparency unless you're using color keying (i.e. declare a specific color to be transparent). But that's not built into SFML/stb_image by default (when saving images).

 

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