The wonderful and missunderstood world of JPEG

[Puffer Fish]

There are two issues on the digital world that people, in general, have difficulty understand... white balance and the issue of RAW versus JPEG.

Before getting to the examples, both good and bad... look at this review of the Fuji DSLR...

Fujifilm S5 Pro Review: 16. Software: Digital Photography Review

No difference between the JPEG and the RAW??? How can that be?

[Puffer Fish]

First off, a camera JPEG is more than just a compression of the image, the camera also does a lot of things to the data...it applies some sort of sharpening. It makes some contrast and color adjustments. It applies the white balance calculation....here, we are just going to look at the JPEG... those other things do a lot...but lets start with one part at a time.

As a reminder, a picture is just a bunch of "dots", that each one has some numbers attached to. Put all the dots together, and you will have an image. For the most part, if you are using windows, that is something called sRGB, where the R= Red, G=Green and B = Blue. three numbers for each dot, and you have a color... all the color you can see on a screen are represented by 0 -256 for each value. That equals over 16,000,000 possible colors, which is more than any human can see.

[Puffer Fish]

Second, JPEG is not a single standard, it is the format for a whole bunch of standards. There are (depending on how one looks at the), either 12 steps, with 12 types of chroma subsampling.... for 144, or 99 (1 to 99%) times 12 for 1188 different versions, add in some other forms, and one gets a confusing number.

Interestingly, almost every camera maker uses a different type, some that work great, some that don't. And it turns out, there is a way to know which they are using...

[Puffer Fish]

The resolution chart, on DPreview.com, is the same image each time, so the resulting JPEG is a reflection on the compression method they use... here are some common camera's

Note: I have adjusted the number to a 10 meg size, so the amount of compression is the same:

Canon EOS 40D -------- 2645
Nikon D200 -------------2728
Pentax k10D-------------2271
Nikon Coolpix 5100 -----2732
Canon Power shot G7----3330
Fuji F50fd ---------------3636
Canon Power shot G9 ---3432

Notice anything odd.... why would the smallest camera, have the largest JPEG.. and why would the DSLR's, have the most compression?

This might help... the Fuji S5----4346

Turns out, a lot of DSLR's don't expect one to use the JPEG, so they put a not so good JPEG in their camera.

Fuji, actually expects their JPEG to be used, and it is a lossless JPEG...


Note: A bit of the size difference is also due to the amount of detail, the more there is in the image, the larger the file will be... this does not represent that much, and one could easily point out the DSLR's actually do have more data, so the difference is actually bigger than shown.

[Puffer Fish]

From the above, one would highly recomment, that with most DSLR's you only use RAW, but that is not the case with the Fuji. If you own a camera, you should check this, to see what they are using.

[Cheddarchick]

Thanks Puffer....I love reading about photography

[Soonerwink]

Thanks Puffer keep the threads coming, I am learning alot from them.

[Puffer Fish]

Ok, so we know they are using different ones.. but which ones, and does it effect the picture?

One would assume that compression is bad... but not in this case...

Remember there are degrees of compression, and different amounts of chroma subsampling.

I will skip over the details of what the JPEG program is really looking at (post if you would like the technical details), the the first level is called:

YCbCr 1x1 1x1 1x1

This is a completely lossless pattern, what it saves will be exactly like the original, if the compression is set to 1%.

I used an image from DPreview, that is a raw D200 picture he uses for testing. I checked the detail (the exact distribution of the pixels and their individual counts) and saved this image with a 1x1 1x1 1x1 and 1%... here is a small section to compare the information:



Here is the compressed JPEG:



If you have any good photo software, please download and compare these two images.

[Puffer Fish]

Originally Posted by Cheddarchick

Thanks Puffer....I love reading about photography

Thanks... am trying to provide as much hard information as possible.

[Puffer Fish]

Originally Posted by Soonerwink

Thanks Puffer keep the threads coming, I am learning alot from them.

Thanks for taking the time to read them...