Negative - Sepia - GreyScale

[Progesco]

I am new to image processing. According to my textbook, I know how to get a negative image (by subtracting them from the number of gray shade: 0 becomes 255, 1 becomes 254, etc), but they didn't say anything about Sepia and GreyScale. I think these 2 kind effects often appear in some software or even camera
Could you explain to me how to get them?
Thank you :)

[Bazzy]

A gray scale image, represents its luminance. You can get this effect by setting each value to the average of all the three RGB values
eg: RGB 128,255,68 -> 150,150,150
Sepia is similar but you apply the gray scale values to the sepia color

[Progesco]

thank, I made grayscale effect.
could you explain more about sepia effect? I don't really understand your hint.

[Bazzy]

It should be something like this:
R = grey*SepiaR/255
G = grey*SepiaG/255
B = grey*SepiaB/255
Where grey is the value you got in the grey scale, the sepia values are these: http://en.wikipedia.org/wiki/Sepia_%28color%29

[z05DSL3A]

Conversion to Luminance is more often carried out like
Y = 0.2126*R + 0.7152*G + 0.0722*B
then set your RGB values to Y.

For the averaging method
RGB 127,197,58 (green) => RGB 127,127,127
RGB 58,127,197 (blue) => RGB 127,127,127

This method:
RGB 127,197,58 (green) => RGB 172,172,172
RGB 58,127,197 (blue) => RGB 117,117,117

http://en.wikipedia.org/wiki/Luminance_(relative)

[Progesco]

I have a question. Is GreyScale color image or not?
If I find average of all three RGB values, then set each value to it, does it mean GreyScale still have 3 channel?

[helios]

Only if the destination surface has in fact three channels. The gray scale operation could take surfaces of different color depths as the destination.