JPG files sizes, DPP vs Out-of-Camera

[E-Man]

I've been noticing over the past little while that JPG files made with DPP (converted from RAW) seem to be significantly larger than those that come directly out of the camera with my 40D.

Out-of-Camera JPG files seem to run 1.5 to 3.5 megs, while ones converted from RAW files with DPP run closer to 6-8 megs.

One file in particular generated a 3.3M file straight from the camera (saved to CF card as both RAW and highest quality JPG), but when I convert to JPG from RAW using DPP, I get a file that is 8.4M.

What causes this difference? The only thing that I can think of is that I use 300DPI in DPP while saving a JPG file (image quality is set to 10, and no resizing is used).

Is this a "normal" result? If it is caused by the 300 DPI setting I use in DPP, what is the default Out-of-Camera DPI setting?

Thanks!

[E-Man]

Explore some more, I just discovered the Out-of-camera JPGs seem to be recorded as 72 DPI, vs the 300 that I set with DPP.

Upon closer inspection, though, one of the 300 DPI images has far more noise than does the 72 DPI file (I was looking at them at 1000%).
So, I took another RAW file and converted it to JPG with DPI settings of 72, 100, 150, 200, and 300 DPI. All file sizes are identical (much larger than straight from the camera) and there is no difference in noise when viewed at exreme magnification...

Can someone please help me understand what is going on here?

Thanks!

[12stones]

I would look at your DPI settings for OOC jpg. For good print quality, most printers recommend 200-300dpi for your images. 72 isn't going to be enough, IMO.

[E-Man]

Hmmm.. I'll have to go through the manual and settings again - I'm not recalling an option beyond the Image Quality - I thought I had always selected the highest quality JPG in the past. Perhaps I missed something along the way.

[matthewlrigdon]

Forget DPI in this case. It has nothing to do with digital imaging. For a much longer explanation, check out this article.

JPEG is a lossy compression scheme. It relies on a body of technical research that determined what colors and details are overlooked by the human visual system and can therefore be thrown out of an image. There are levels of how much data you throw out when you create a JPEG. Most program use a scale from 1 to 10 or 1 to 100 (although Photoshop's Save As... command uses a 1 to 12 scale) that determines how much compression is applied to your image. The in-camera JPEG setting is far more aggressive than what you're using in DPP. That's why the file sizes are smaller. Generally, this is a good thing. If you're shooting JPEG out of the camera, you're more concerned with image size and saving post-processing time over higher quality.

It's been awhile since I used DPP, but I imagine that since it's using RAW files as its starting point, the highest quality image you can pull from the camera, it figures you'll want to use a very low level of JPEG compression. In fact, JPEG settings of 10 (or 12 if you use Photoshop Save As...) result in near lossless compression (I'm not completely sure that it's truly lossless, as it may still downsample chroma to some degree, an operation that's generally considered to be indiscernible to the human eye).

[E-Man]

Thanks for your reply, Matthew! I suspected it had something to do with compression ratios, and just wondering if I overlooked a means to control it, or if it was "hard wired" into the algorithm. I didn't consider your point on Canon "interpreting" my intent by selecting output as JPG or RAW. I can see them deciding that if you chose JPG, that you might be more interested in the number of images that will fit on the memory card.

I'll have to play around a little bit more now that I have "discovered" this behavior.

[Max@Home]

as matthewlrigdon said: forget DPI, it is a PRINT thing, telling the PRINTER how 'dense' you want to print. The only thing that will effect image size in-camera is resolution, amount of light (= data) in the image and how high you set ISO (higher ISO is higher 'noise': black (=no data) becomes 'greyish' (= data))...

...the difference in image quality between a 'quality 10' saved DPP-JPG and an OOC-JPG is visible when you make large prints...

...and if 'the best converter' gives the largest JPG files in Best Quality setting, reasoning 'the more Mb, the more detail/info' then DPP is the best converter for Canon RAW files ...

...€0.02...

Kindest regards!

Max@Home

[E-Man]

Thanks, everyone! I think I get it now... It would be nice for (all) manufacturers to include these details in a good user's manual so we didn't have to stumble through it on our own.. But then, I'm more of a gear-head than most people.

[aam1234]

It also depends on quality setting you have in DPP for conversion. Going from say, Q7, to Q9 will make a huge difference in file size. That's why my default setting in DPP is Q7, and when I want to print I go back to the photo and save it at Q10.

[E-Man]

I've always understood the IQ settings in DPP and its relationship with file size.

For each pixel size setting in the camera (typically Small, Medium, and Large), there are two image quality settings (High and Low). I had assumed that camera settings of 'Large' JPG set to 'High' corresponded with an IQ setting of 10 in other graphics processing software...

This wouldn't be the first time that my assumptions have gotten me into trouble, as this seems not to be the case here.

[E-Man]

OK, more playing around comparing OOC JPG images from my 40D with those produce with DPP. It looks like the OOC JPG files are approximately equal to Image Quality setting of 7 to 8. No single conversion that I did hit an exact match for file size. Using file size as the metric, some OOC JPG files landed between 7 and 8 in terms of IQ setting. Other were slightly larger than IQ setting of 8, others were smaller in size than IQ setting of 7.

Nothing like a good DIY mystery to solve!

[aam1234]

Originally Posted by E-Man

Nothing like a good DIY mystery to solve!

You Da Man, Eric. Thanks for the experiment and info.