It is smart of you to post photos that you have not yet edited. However, if the photos were recorded on the memory card as JPEG image files, they were extensively edited in the camera before the camera made them available for you to see on the rear LCD.
The image sensor of your 400D (XTi here in America) captures a Raw image data file that has at least a 12-bit color depth every time you release the shutter. That is 12-bits (4096 colors) of color depth per each of the 3 color channels; red, green, and blue (RGB), or 32-bits of color data.
If your camera is set to record JPEG files to the memory card the Raw image data file is edited in the following ways:
- All but 8-bits of the color depth recorded at shutter release for each color channel is discarded. 8-bits can only render 256 colors per color channel, so 3840 colors are discarded from each RGB color cannel.
- Based on programming decided on by a committee of camera software engineers, not you, the global contrast, saturation and sharpening of each JPEG file is edited. The camera does have some additional, although crude menu settings that let you increase or decrease the amount of those global edits.
- The pixels in the image are converted to 16 by 16 pixel, 16 by 8 pixel, or 8 by 8 pixel groups known as Minimum Coded Units (MCU's)
So, it's good you don't do anymore editing because JPEGs have little, if any, editing headrooom left after the camera has edited them.
I used the term 'global edit'. That is an edit that is aplied to the entire image. Local edits are often desirable.
Consider when a wide aperture is used to selectively focus a subject (shallow DOF) so the background is blurred. It doesn't make much sense to then apply a global sharpening edit that will reduce that background blur as well as enhancing details of the in-focus subject. Using image editing selectioon tools just the subject can be selected and locally sharpened so the blurred background is excluded from the shapening edit.