Working on RAW files
Work on RAW file is the first step to learn, to approach to the post production process. Is something like a negative in film photography. To develope a jpg or tiff file, the best way is to work on a RAW and convert it at the end of modifications. Work directly on compressed files, is possible but don't permit to have same number of data of the file. RAW files are in 12 or 14 bit, JPG are 8 bit: this is very important because defines how many datas we have for every single color of the image. It is possible to shoot directly in compressed format (jpg), but to obtain the best quality from the camera, I recommend to use the digital negative format. Use softwares like photoshop guarantees a big difference compared to the automatic settings of the camera. Every brand have a different raw format with different extension. I usually use Canon Cameras and .cr2 is the own format, moreover every model of the cameras have different datas in the files.
Is possible to open or convert RAW files with many softwares and usually when you buy a new camera, one converter is included in the box. Commonly I use Photoshop to work on my pictures and the raw's manager is called "Camera RAW".
First thing to do is open the file with camera raw. The image will be loaded with the possibility of modify some parameters. Since these parameters are the same it is possible to find in photoshop, but the instruments are not detailed like in the program, my advice is to do this modifications in a second moment with more instruments. Before open the file in photoshop, check if your raw file is 14/16 bit (set the highest resolution) and set all the parameters to 0 except the brightness (+50). Verify the other tabs to have all parameters set to 0 and then open the file.
If the picture is underexposed or overexposed, sometimes is possible to change this parameter in "camera RAW". But 80% of my files are managed with all settings on 0 and brightness (+50).
When the file will be open in Photoshop, you will have a flat image but will be possible to work on more details of the photo.
From now you can use all the instruments available in the program, to process the image and get the final file to print or to pubblish...