Editing JPEG (section)

====Color space transformation====
First, the image should be converted from RGB (by default sRGB,<ref name="auto"/><ref name="auto1"/> but other [[color space]]s are possible) into a different color space called [[YCbCr#JPEG conversion|{{YCbCr}}]] (or, informally, YCbCr). It has three components Y', C<sub>B</sub> and C<sub>R</sub>: the Y' component represents the brightness of a pixel, and the C<sub>B</sub> and C<sub>R</sub> components represent the [[chrominance]] (split into blue and red components). This is basically the same color space as used by [[digital television|digital color television]] as well as digital video including [[DVD Video|video DVDs]]. The {{YCbCr}} color space conversion allows greater compression without a significant effect on perceptual image quality (or greater perceptual image quality for the same compression). The compression is more efficient because the brightness information, which is more important to the eventual perceptual quality of the image, is confined to a single channel. This more closely corresponds to the perception of color in the human visual system. The color transformation also improves compression by statistical [[decorrelation]].

A particular conversion to {{YCbCr}} is specified in the JFIF standard, and should be performed for the resulting JPEG file to have maximum compatibility. However, some JPEG implementations in "highest quality" mode do not apply this step and instead keep the color information in the RGB color model,<ref>{{Cite book|url=https://books.google.com/books?id=bYxMVVzdV80C&dq=A+particular+conversion+to+Y%E2%80%B2CBCR+is+specified+in+the+JFIF+standard%2C+and+should+be+performed+for+the+resulting+JPEG+file+to+have+maximum+compatibility.+A+particular+conversion+to+Y%E2%80%B2CBCR+is+specified+in+the+JFIF+standard%2C+and+should+be+performed+for+the+resulting+JPEG+file+to+have+maximum+compatibility.++A+particular+conversion+to+Y%E2%80%B2CBCR+is+specified+in+the+JFIF+standard%2C+and+should+be+performed+for+the+resulting+JPEG+file+to+have+maximum+compatibility.+&pg=PA53|title=E - Learning Modules: Dlr Associates Series|last=Ryan|first=Dan|date=2012-06-20|publisher=AuthorHouse|isbn=978-1-4685-7520-0|language=en}}</ref> where the image is stored in separate channels for red, green and blue brightness components. This results in less efficient compression, and would not likely be used when file size is especially important.