15.6 JPG Compression Artifacts

Figure 15-10: The source image for the .jpg compression comparisons in Figure 15-11.

One thing about the JPEG compression standard that wasn’t specified was how much to compress the image – this is usually up to the user. The JPEG standard allows you to specify a “quality” level of one to ten, ten being the best quality. The tradeoff is file size, for as the compression gets higher, the file size gets smaller and the image quality gets lower.

For an extreme example of the quality tradeoffs the JPG format offers, have a look at Figure 15-11. These examples were made using an older software package which allowed me to specify the .jpg compression levels from 1 (best) to 100 (worst). These extreme examples are being used just to give you an understanding of the correlation between file size and image quality. In real life, you would probably never want to store the image using the worst quality settings (unless you were writing a book that wanted to show .jpg compression artifacts :-) ).

TIP: Today’s out-of-camera .jpgs look outstanding compared to those of 10 years ago, making it safe for photographers who have good light and whose exposure is right for that light to shoot .jpg exclusively. For more insights on such heresy, see my blog post entitled, “Where the anti-JPG bias came from” here: http://tinyurl.com/7m327cj and the follow-up here: http://tinyurl.com/8kkfpsh.

Figure 15-11: Extreme examples of JPG compression artifacts. (Don’t try this at home, kids!)

IMPORTANT TIP: These compression artifacts can get worse the more you work with them. Every time you open-modify-save-close a file, the file is re-compressed, adding more compression artifacts to whatever was already there. To avoid this (and in keeping with the mantra of NEVER OVERWRITE YOUR ORIGINALS), always go back to a copy of your original before making any modifications, and make sure that you make all of your modifications in one session before saving as a JPG.

Your camera allows you to save your images as .JPG files with three quality formats: “Standard” (not to be confused with the “Standard” Creative Style discussed in Section 6.26), “Fine”, and “X.Fine”. You can switch between these modes by invoking MENU --> 1 --> Quality --> [Choose one]. Most people would have to examine an enlargement with a microscope in order to see the differences in quality between these three settings in good light. Just as not everyone can hear differences between .wav and .mp3 digital audio file formats, not everyone can perceive the difference in image quality between RAW and JPG, or between different qualities of JPG. Try shooting in all 3 modes, printing the results at 8.5x11 or A4, and see if you can tell the difference!

So, in summary…

RAW (*.arw)	A “dump” of all the bits from the sensor. Large file size. Requires post-processing on a computer by hand. Designed for professionals who demand the highest image quality. Almost a necessity when shooting in low light and high ISO to get both low noise and detail in your final print. Modern RAW files are compressed using a nearly-lossless compression scheme.
TIFF (*.tif)	(Not created by the camera, but exportable from RAW via Image Data Converter and 3rd party programs such as Photoshop.) Same information as RAW, plus the color, contrast, and other factors are applied. About 3 times larger file size than RAW, but unlike RAW it can be read by most other applications. TIFF and RAW produce the highest quality images because there’s no .jpg-like loss due to compression.
JPEG (Standard, Fine, and Extra Fine) (*.jpg)	Very high image quality with substantially reduced file sizes (see comparison table below) due to innovative mathematical compression techniques.

 

A comparison of the different file sizes and quality levels can be seen below (and these are identical to the table appearing earlier in the book in Section 6.3). This is with the compressed RAW feature turned on:

Image Format	File Size	JPG Quality Equivalent in Photoshop
Standard (.jpg)	4.0 MB	Quality = 10+
Fine (.jpg)	6.2 MB	Quality = 11+
Extra Fine (.jpg)	12.5 MB	Quality = 12+
RAW (.arw)	24.2 MB
RAW + JPEG produces 2 files	24.2 MB (.arw) + 6.2 MB (.jpg)

 

It is interesting to note that, even for the “standard” (lowest quality) .jpg setting, the compression is very conservative, and the image quality is still quite high.

TIP: The sizes of .jpgs vary greatly. For example, my “FINE” quality .jpgs vary in size from 2MB to 8 MB, depending on the amount of high contrast detail in the subject. So if you try this experiment yourself, don’t be surprised if your numbers are off by a factor of two or more. This is why the “Images Remaining” counter shows you conservative numbers – often you can fit more images on a card than what the camera shows you when an empty card is inserted. The camera never knows how large your .jpg’s are going to be.

 

15.7 Any Other Upsides to Shooting .JPG?

Well, we already know that they take up less space and they (potentially) require less work for post-processing. And you already know (having read the blog post I pointed to earlier at http://tinyurl.com/7m327cj and its follow-up, http://tinyurl.com/9h9fju6) that if my light is good and my exposure is right for that light, I sometimes will shoot only X.FINE .jpg since the benefits of RAW in that scenario are not compelling. Are there any other benefits to shooting .jpg?

Yes, I can think of three more:

• You may not know this, but your camera keeps a database of the optical deficiencies of most native E-mount lenses (distortion at various zoom distances, chromatic aberration, and darkening in the corners) and it corrects for all of these deficiencies in software automatically – but only to .jpg files. It also stores the suggested corrections in every RAW file it writes (without actually applying it) so programs like DxO, Lightroom or Bibble can correct for it automatically – you don’t have to create a special lens profile first.
• DRO shadow lightening (Chapter 14) is not applied to RAW files, although you have the option of using Sony’s IDC software to give you a close approximation to the in-camera algorithms. Global editing parameters in other packages such as “fill light” do not do the same thing as DRO. Many people in the past had complained that it takes too much time to try to re-create what DRO does using Photoshop.
• A lot of your camera’s best features, such as Multi-Frame noise reduction and High Dynamic Range, work only when shooting .jpg (by definition).

Is now a good time to mention the joys of “RAW + JPG”? Shoot now, decide later. All the options are kept open for you.

TIP: Once upon a time there was an esoteric noise reduction technique called “Expose to the right” (ETTR). The idea behind it was to overexpose the image when you’re shooting RAW (taking care that you didn’t blow out your highlights) and then bring the brightness down later in your computer. It really worked! (And I gave an example of this in my Advanced Topics 1 e-booklet).

Recently someone at Sony decided to optimize the way brightnesses were distributed within the newer RAW file standards, meaning there’s now better quality when shooting in good light but the ETTR technique is no longer as effective. An article on SonyAlphaRumors.com (which summarizes an even more technical dpreview thread) is here: http://tinyurl.com/5s335pq. If you love technical details then read the referenced dpreview thread all the way through – they’re talking about an earlier camera, but the light distribution representation of the RAW file is the same.)