Introduction

On my last post I talked a bit about how a digital camera works in capturing images. However, the set of numbers from the sensor representing the image as the camera sensor sees the world, is not the end of the road for the digital image. From the sensor the data is still “RAW” or unprocessed and before a nice image can be seen this unprocessed image needs some work to get it into a form that things like monitors and printers can understand. This article explains in a bit more detail what happens to your image as it comes off the camera’s sensor and its road to your monitor.

Inside the camera

I think the best way to explain what happens in the camera is at the hand of a little drawing.

Inside the camera

Yes, after looking at my drawing you know why I take pictures and not draw! Anyway, this drawing in very simple terms explains what happens in the camera. The camera forms a “RAW” image with the data received from the sensor. Now, according to the settings you chose the camera can either store the RAW data as is to your camera’s storage medium (I called it disk) or it can pass the RAW information to  it’s internal “JPG Engine” that is responsible for converting your RAW image to a JPG file which is then stored on the camera storage medium. Remember that RAW is not a specific file format like JPG. Instead it is a description for unprocessed data. The format that a specific camera will use to store RAW data on the camera disk depends on the camera manufacturer. For example, Nikon RAW files will be stored as NEF files. So when someone says that they shot an image in RAW, they mean that the image was never passed to the camera’s JPG Engine but was instead stored in it’s raw format on the camera’s disk.

The JPG Engine is also often called the Image Processor of the camera. The image processor takes as input a lot of information supplied by the user through camera settings and together with the information the camera has regarding the light as well as pre-programmed factory settings will process the RAW image data into what it thinks is what the image should look like. It will adjust things like contrast, exposure, saturation, hue, black levels, brightness etc. and finally save the adjusted image as a JPG file to the camera disk for storage. It is important to note that during this process of adjusting the image from RAW to JPG a lot of information is lost from the original RAW information. Further information is lost when the image processor writes the JPG file because JPG is a compressed format while RAW is usually not compressed (but can be very slightly).

To RAW or not to RAW

The photographer that took his image in his camera’s RAW format ends up with an unadjusted image. The first thing he needs to do after downloading his image from his camera is to convert the RAW image into a usable format. When doing this he will have to adjust all the parameters, that the JPG engine does for the photographer inside the camera, by hand (or by automated calibrated software). So what is the difference. Well, the photographer that uses RAW will adjust the image according to his own eye and liking while the JPG image straight from the camera is adjusted according to what the camera thinks is a good image.

Thus, JPEG straight from the camera is as good as the pre-programmed JPG Engine software supplied by the manufacturer. It is also camera dependant in that every camera manufacturer use its own software. Some cameras have bad image processors and others have good image processors but at the end of the day nothing beats the human eye.

Conclusion

It is up to the photographer to decide where he wants most of his post processing to happen. Yes, the image processor inside the camera also performs post processing. When shooting RAW the post processing is more involved in that the photographer has to convert from RAW to some other format before the image is “usable’. In both cases, after the image was converted to either JPG (inside the camera) or to some other format (e.g. JPG, TIFF etc) outside the camera on computer, the photographer still has the choice and opportunity for further post processing e.g. adjusting levels, contrast, hue, saturation, brightness etc. Post processing is time consuming and time is a very good motivator to use JPG straight from camera.

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