I have a Panasonic DMC-FZ50 camera, no longer produced, but it was at the top of Panasonic's line.

SWMBO has a Panasonic DMC-FZ28 camera, considerably less expensive and not as feature-rich.

Both cameras shoot at 3648 x 2736 resolution, ~10 megapixels.

If I look at photo properties for a picture from the FZ50, it says 72 dpi for horizontal and vertical resolution.

If I look at photo properties for a picture from the FZ28, it says 180 dpi for horizontal and vertical resolution.

Pictures from either camera seem comparable to look at.

Am I confusing dimensions (3648 x 2736) with resolution (72 dpi vs 180 dpi) and does that mean that the FZ28 has more than twice the resolution of the FZ50?

What do these numbers mean?

tanstaafl.

Resolution is the number of pixels that you get. DPI is how closely packed those pixels are.

The differing DPI values are either the firmware just putting in some preset value or the actual sensors in the camera are different size.

DPI for a camera doesn't really make much sense. Well, I suppose it could be the DPI of the sensor, but that would be in the range of thousands, not hundreds. Beyond that, how do you translate pixels to inches for a photograph? You don't; it's a ridiculous conceit. (Obviously it does make sense for scans, but we're not talking about scans.)

In all likelihood, it's just bogus data put in there by the camera manufacturer to fill the field.

"Resolution" actually means both things and in fact means also a few others, such as how many lines a lens can resolve at a certain focal length, etc.. That tends to be a big problem if you don't specify what you're resolving.

Most people in this forum, including myself, will use resolution to talk about the pixel dimensions of an image or screen. So Trevor is totally correct.

The DPI setting in the camera is only of benefit when printing the image or rendering it with a print intent. Neither number in the DPI of the photos is bogus however. I can't be certain why Fuji picked 180 specifically, but I do know why the first camera is set to 72.

"72" is the traditional screen pixel density and also how many points fit in an inch. It's typical to have screen-based images set to 72 DPI if for not other reason that to not have undefined or unusual (non-historical, non-common) numbers in the DPI field of the metadata. Most modern screens are actually much higher density than 72 DPI, or more correctly, PPI - since the "D" in DPI means dots, in colour printing it can refer to the individual droplets of one single primary colour, or is sometimes used to refer to a single primary colour in an RGB triplet. That's how you get huge DPI numbers on cheap printers and huge numbers on camera LCD specs.


The 180 value is likely the attempt of Fuji to set the value at something more meaningful for printing, which would leave you with a ~20x15" print, reasonable for that sensor. That's what you'll get without adjusting the DPI/PPI setting yourself either manually or through some other scaling operation, when printing/rendering with software that's aware of those settings, such as Photoshop or even Preview in Mac OS.

You can change that setting without altering the pixel dimensions at all to manipulate the printed size of the image. Some software will let you adjust the printed size directly in inches without touching the image data, so it's also really affecting only the DPI/PPI.

If you're going to print 4x6, reduce the number of pixels in your output images before you send them off to save time/space in file transfer. And possibly also be left with better output due to smoothing and other settings you can apply in software like Photoshop when scaling.

To help clarify the difference between DPI and resolution, imagine this scenario:

- You have a photo on your hard disk, the file contains image data that is 1000 pixels wide.
- You print that photo on a piece of 5-inch long photo paper in "fit-to-page" mode. What's the DPI of the photo?
- You then reprint that photo on a piece of 11-inch long photo paper in "fit-to-page" mode. What's the DPI of the photo now?

Or better yet...

- You view that photo using a video projector at 1:1 ratio, so that 1 pixel on the projector is 1 pixel on the file.
- You have the projector 12 feet from the wall so the image on the wall is about 6 feet wide. What's the DPI?
- You scoot the project up really close to the wall so that the image on the wall is about 1 foot wide. What's the DPI?

You can see that, for the source image file itself, DPI is utterly meaningless. Any DPI number that happens to be attached to the file is arbitrary. DPI only counts for physical output: How many pixels per inch in the final output stage. Whether that physical output is a printer, an LCD monitor, or whatever.

Now, to confuse things...

Many CCDs don't use rectangular elements in their arrays. I know some of them have hexagonal pixel elements and they convert the results into X/Y arrays of pixels using the camera's internal electronics and then save that file for you to transfer to your computer. The claimed resolution of any given image from the camera becomes even murkier there.

Many? The only one I know of for the consumer digital world is the Fuji SuperCCDs which have variations on the octagonal pixel. Everybody else in the consumer digital world uses rectangular pixels.

To put it more succinctly, the immutable numbers are the 3648 x 2736 pixel numbers. The 72 and 180 dpi numbers are scaling or mapping numbers.

If you change the former, you have altered the picture. If you alter the latter, you've really not done much of anything.

The idea is that pixels have no defined physical dimensions. By applying a DPI or PPI mapping to them, you can establish dimensions.

At best, though, they're suggestions. But since your pictures don't have any logical pixel-to-inch mapping (for example, in your panoramic photo, there's a column that occupies many more pixels than a palm tree just above it, and that palm tree occupies more pixels than a five-story building somewhat farther above), the only thing that they can indicate is how large to print out the image, and you're going to ignore that anyway.

How would you really know? The CCD digital signal processing circuit is going to translate the odd-shaped pixels to rectangular ones so you aren't going to know just by looking at the output.

I was under the impression that the Panasonic cameras used CCDs with hexagonal arrays. I could very well be wrong about that, though.

Its published or people work it out. If you look at the reviews on dpreview, you'll see that they list things like actual number of pixels on the sensor, effective number of pixels on the sensor, arrangement of colours in the filter and a whole bunch of other information.

As for whether you can spot the difference yourself just by looking at the output then no idea.

SuperCCD is advertised as a unique feature of Fuji cameras since as Tony previously said, it alledgely gives you a higher effective resolution than the actual number of physical sensors in the CCD.

As for other cameras, any deviation from the regular image sensor is generally noted in the specifications. Canon use a different set of colour filters which again apparently give better results than the regular colours. Sony use another arrangement etc...