METADATA JPEG vs. RAW

Hey Gang,

I have a question for those that are familiar with the Metadata for .JPG vs. RAW outputs. I have yet to print with RAW or converted RAW to JPG, but noticed some Metadata differences that raise some questions for me.... Take a look at the following Metadata of a particular photo that was captured with both .JPG and .CR2 (RAW);

METADATA (from Adobe Bridge)

.JPG (output)

File Size; ~4.5M

Dimensions; 3888x2592

Dimensions (in inches); 54.0"x36.0"

Resolution; 72ppi

Bit Depth; 8

Color; RGB

Profile; SRGB

.CR2 (RAW output)

File Size; ~13.6M

Dimensions; 3888x2592

Dimensions (in inches); 16.2"x10.8"

Resolution; no data

Bit Depth; 16

Color; no data

Profile; no data

.JPG (converted RAW)

File Size; ~6.9M

Dimensions; 3888x2592

Dimensions (in inches); 16.2"x10.8"

Resolution; 240ppi

Bit Depth; 8

Color; RGB

Profile; Adobe RGB

The question is, "At full print size do I have the same print resolution quality with .JPG vs. CR2?" Above, notice that the "Dimensions" Metadata are the same throughout for .JPG, CR2, and converted CR2, etc.. However, notice the "Dimensions (in inches)" for .JPG vs. CR2, there is a huge size difference?! The CR2 output is roughly 1/3 the size of the .JPG output.... What does this mean? Without knowing any better I would interpret this data to mean my print max for the .JPG file vs. the CR2 file is 3x bigger, or as the data says the picture size max for the JPG is 54"x36" vs. the CR2 of 16.2"x10.8"....

Can any of you please explain what the data really means. Also, the "Bit Depth" Metadata, I'm assuming the 8 bit vs. 16 bit is the JPG compression vs. uncompressed RAW... Same thing with the "Resolution" the 72ppi vs. 240ppi...

Thanks

Derek...

The difference between "print size" is because the resolution settings are different. The resolution isn't really respected since most of the time the image is scaled to fit the print size. The first JPG has a resolution of 72dpi so the "print size" is 3888 dots x2592 dots /(72 dots/inch) = 54 inch x36 inch. The RAW mode doesn't have a dpi setting so the software is apparently using 240dpi as a default, etc. You can change the DPI setting in photoshop without resampling the image so you can think of is as an "informational only" parameter.

The bit depth is the number of bits per color per pixel. For your .CR2 image, each pixel is represented at 16bits each of R, G, and B. Of course the camera only fills in 12 bits or 14 bits, so each pixel will have the upper 4 or 2 bits as zero. When Photoshop is in 16 bit mode, it carrys around these extra bits in the calculation to guard against roundoff error. JPG images are always 8 bits per pixel. I think JPEG2000 allows 16 bits. The reason you can get by with 8 bits is that JPG images have a logarithmic intensity scale, whereas the RAW mode images are linear.

A very good explanation.

I could add that 72dpi (ppi) is suitable for viewing on a computer screen but publications usually ask for files at 300dpi min. for mechanical reproduction. The computer screen is very seductive.

The difference between "print size" is because the resolution settings are different. The resolution isn't really respected since most of the time the image is scaled to fit the print size. The first JPG has a resolution of 72dpi so the "print size" is 3888 dots x2592 dots /(72 dots/inch) = 54 inch x36 inch. The RAW mode doesn't have a dpi setting so the software is apparently using 240dpi as a default, etc. You can change the DPI setting in photoshop without resampling the image so you can think of is as an "informational only" parameter.

 

The bit depth is the number of bits per color per pixel. For your .CR2 image, each pixel is represented at 16bits each of R, G, and B. Of course the camera only fills in 12 bits or 14 bits, so each pixel will have the upper 4 or 2 bits as zero. When Photoshop is in 16 bit mode, it carrys around these extra bits in the calculation to guard against roundoff error. JPG images are always 8 bits per pixel. I think JPEG2000 allows 16 bits. The reason you can get by with 8 bits is that JPG images have a logarithmic intensity scale, whereas the RAW mode images are linear.

Thank you Steve and John! I follow perfectly, but I still would like to lead query a bit further...

BTW, when I took the RAW image into PS I was able to save the shot to 72dpi and consequently could see that the dimension in inches change to a higher dimension of 54" x 36". No problem, I get the scaling of the dpi to adjust the resolution... I also now understand that the acceptable dpi for web viewing is not necessarily good enough for publishing, which leads me up to high quality photo printing, and maximizing that quality.

New question; At what point on a high quality photo printer do we get diminishing return on the resolution of the photo we are trying to print? For example: If I have a photo printer capable of 4800x2400 dpi (which seems to have far more resolution than any photo that I could feed it).

Now are the following statements correct;

Given a JPG image that was 3888x2592 (54"x35") @ 72dpi, would you have the following print resolution based on the following print size:

Print size: 54"x35", 72dpi.

Print size: 27"x17.5", 144dpi.

Print size: 13.5"x8.75", 288dpi

Print size: 6"x4", 648dpi

Assuming the above dpi's are correct a couple things could be said:

1. The smaller the print the sharper and more colorful the output will be (based on this printer 4800x2400dpi).

2. The dpi is automatically resolved by the print driver to the paper size you are using (more dpi on smaller paper format).

3. You can't reach the print resolution of this printer (4800x2400dpi) in this case.

4. If printing the same shot that was saved in a RAW format, you don't get better print resolution, in fact, the JPG and RAW are equal in terms of print resolution.

I noticed that Steve and John both used dpi (dots/in) and ppi (pixels/in) to have the same meaning. Can you really call them the same in terms of resolution? In other words, are they really one for one?

Cheers

Derek...

This may not answer ALL your questions, but this site is a good reference for certain technical topics ... figured I'd throw it out there ...

http://www.cambridgeincolour.com/tutorials.htm