Legacy ImageMagick Discussions Archive

For the reference the input and output images side by side in Photoshop.
Notice that the building to the right is brighter.

Guys, thank you for responding so quickly!
I have a PNG image in sRGB format.
All three RGB channels contain the same values.
I just need to extract one of them (Red, for example) to a file in grayscale format to save space and memory.

I've tried the spells proposed by Fred.
Unfortunately, they ...

I need to extract Red channel from a PNG file.

I use this command.
convert image.png -channel R channel.png

Unfortunately brightness is slightly increasing in pixels of the output image.
For example a pixel with red value of 100 becomes 132 in the output image.

Now I wonder if I'm using IM ...