Save Dialog - JPEG subsampling

The save dialog of PhotoPerfect is definitely one of my favourites, since I really like the "determine quality" and "determine file size" functions to optimize the size of my final saves with nearly no effort.

But I always wondered when exactly I should use the selector at "JPEG subsampling". Unfortunately the manual doesn't really elaborate on that subject and thus I am left with guessing if the setting "4:2:0 Standard" is a good choice or if I should rather go for the "4:4:4 Best". Or would that be just overkill and unnecessarily blow up the size of my pictures?

What setting would you recommend and why?

cheers,
PhotoWebber

Hi,

In general, if I have a photo with a lot of fine details, I would choose 4:4:4, as this uses no subsampling at all, thus preserving all details and due to this is also in general sharper than other. For less important stuffs I mostly use 4:2:2. This means a chroma compression rate of 2:1.

4:2:0 is on contrary too much for my taste. But as you already know - taste differs. So depending on the content of your photos and your subjective perception, other settings might be more suitable. If you would like to find out what settings suit best to you, I highly recommend to utilize the "Delta preview" in the save dialog. It objectively shows you the image degradation due to compression. The more you can see on the delta preview screen, the worse is the compression. If you can't see anything but a gray layer, then your combination of subsampling and compression rate is perfect ;-)

If you would like to learn more about the technical background of JPEG subsamplings, the following sites might be of interest to you:

http://www.ampsoft.net/webdesign-l/j...mpression.html
http://photo.net/learn/jpeg/index.html

Hope this helps a bit.

Cheers

Hoang-Tran

Thanks for the detailed answer. But if 4:4:4 is recommended, why is 4:2:0 the standard setting of PhotoPerfect? And what exactly happened to my pictures, that I saved using that default setting even when I moved the quality slider to 100%.

I checked some of my pictures again using the the Delta Preview and obviously there has still been some kind of compression that I had thought to have avoided?!?

And where exactly is the difference between the compression factor that you can influence through the quality slider and the compression factor that is applied by the subsampling setting?

cheers,
PhotoWebber

Hi PhotoWebber,

There are 2 parameters that you can set within the JPEG compression.

- Quality setting: In most programms, you can set between 1 and 100- worst to best. This is only an arbitrary scale and tells nothing about the final file size. Depending on your photos and usage, value between 50 and 100 could be set. However if you are quality conscious, maybe values > 75 should be considered. As harddrives are pretty inexpensive nowadays and as a quality freak personally I rarely go below 90.

- The so called chroma subsampling. Possible settings are 4:4:4, 4:2:2 etc...as stated in my last post. It can help reducing the file size tremendously. There is a good article in Wikipedia:

http://en.wikipedia.org/wiki/Chroma_subsampling

Chroma subsampling compresses small areas of colours mostly without noticeable loss of perceived image quality. The reason why PhotoPerfect uses 4:2:0 as standard is very simple. It is the standard used in most JPEG and video compressions
Historically this rate produces a good compromise between (small) file size and "perceived" quality, especially for web usage. Perceived does not means that there is no flaws. It just means that most people would not see it. (The delta preview on contrary shows you all possible degradations.) Besides if your display cannot show you the flaws, there is no need to increase the file size just to reduce them. What you don't know won't hurt you

However nowadays with huge technical progresses in displays, cameras, storage space etc..., IMO there is no more reason against the usage of 4:4:4 and 97 quality setting...but that's just me

Again, thanks for your answer.
Do you know, what subsampling settings the typical cameras use, if you choose their "best" setting?
e.g. a Canon EOS or a Canon Powershot or a Nikon D300 or Coolpix etc.

Do they use the 4:2:0 subsampling or the 4:4:4 or something in between? I am not looking for an answer for every camera, I am just curious what the industry typically chooses when writing pictures as jpegs to the memory cards.

cheers,
PhotoWebber

Hi,

Currently I'm still (the new Nikon are very tempting though ) using Canon DSLR. . They use 4:4:4 with 99 as quality setting in the best JPEG option.

Cheers

Hoang-Tran