Canon 20D in the raw

Channel saturation and artifacts produced by "in camera" JPEG VS RAW

To understand what I'm discussing here, its useful to remember a few things about what happens when you take a photograph with a digital camera:

  1. an array of sensors on a chip record the level of light that fell on them
  2. this level is then converted into a number
  3. some 'signal processing' is done on this data to 'neaten it up'
  4. this data (starting as seperate RED GREEN and BLUE pixels of either 12 or 14bit) are then processed to fabricate a new pixel with RED GREEN and BLUE values in 8 bit per channel
The important thing here is that if this last step performed on your computer the same photograph can give you a 16 bit image. Meaning that picture information in those 14 bits is not compressed or changed without your decision making process.

If you have your own camera that can take RAW images, I encourage you to test it yourself. Set it up on a tripod (if you can). Take an image of the same scene at differing ISO settings and both JPG and RAW. Split the channels and have a look around your self.

Summary of findings

After looking at this on the Coolpix 5000 (with a MUCH smaller sensor and older in-camera JPG conversion engine), I found significant effects in the JPG produced by the camera that would reducethe image quality. I thought it was logical to explore this more carefully on a larger sensor camera with a superior and more modern on-camera image processing system, such as the 20D to see if similar results were found.

My interpretation of the results found is that:

Below is an image taken at 400 ISO with the 20D. I did not use a tripod (whoops) and had the custom function set to save a RAW file and a JPG image. This way I could compare the same exposure as both image types.

strawberrys

The image above is from the JPG image. It looks OK to me at this size. Looking at a section (below) from the the JPG sourced image shows the small strawberry looking a like a bright plastic thing. Hover your mouse over to see the RAW file, and I think you'll find that much better texture remains on the strawberry, as well as in the the appearance of the "out of focus areas of the image". I find that the RAW image retained a natural look, while the JPG looks like its made of pastic.

The answer as to 'why' comes from looking at the RED channel. Looking at the image below, you can see the same in-camera artifacts (though reduced) to what I found on the coolpix and that the RED channel is totally blown out. If you hover your mouse over the image you'll see that the RAW sourced image was not blown out, nor does it contain the pattern effect discussed previously.

WOW. So a significant benefit of using RAW is that greater reach into the highlights can be had. Remember that I'm photographing a red strawberry in low contrast light but already the RED channel is blown out on this part of the JPG.

What about channel artifacts in the JPGS?

Looking at the images below, we can see the same in camera artifacts that appear in the Coolpix 5000 in-camera generated JPG appearing in images from from the 20D. The RED channel (and the blue not shown here) are simmilar, while the GREEN is almost unchanged from the RAW. Curious...

JPG GREEN Channel (mouse over to see RED) RAW GREEN Channel (mouse over to see RED)

I am sure you can see the differences between these two images, as well as the similarities of the patterns to what I found in the Coolpix 5000 in-camera images. However this is where the bigger pixels of the sensor (more so than just the number of pixels) makes the most significant difference as the artifact pattern is spread over smaller area of the image.

As I have shown, the 'distortion pattern' from in-camera processed JPG's is still there, even on cameras with such advanced processors as the 20D. Certainly it is much more reduced, but it remains that if you want to get the BEST out of your image then you should use RAW.

Though the effects produced in the 20D images is far less a problem. In the image below I have the complete colour segment of the above channels. If you hover your mouse over the image, you'll see the RAW sourced image.

I think you'll agree that while they're different, its mainly in colour and contrast. The differences I've found in the layers do not add up to such as significant a difference as they were to the smaller sensor of the compact camera.

If you are at all after lens bokeh then you'll need to be shooting in RAW to capture that to best advantage.

One of the advantages that digital cameras have is that while the images may be of smaller absolute pixel dimensions than what can be scanned from film, they are often so much clearer as to allow printing bigger than for the same pixel dimensions of scanned film. However, when printing camera images at larger sizes and with less pixels per inch having a totally clean image is important. This is where compact cameras are let down and the bigger sensors available to DSLRs really shows.

shooting RAW allows you to get the most out of your image if you want to and appears to be essential for maintaining images of colour smoothness even in the new DSLR cameras.

If you have any thoughts, or would like to discuss this and or my methods, please send me an email to I'd be glad to have a chat ...

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