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Old Jan 5, 2006, 4:09 AM   #1
ViS
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Is there a way to change the dpi output onboard the camera? At the highest JPG setting, when I upload the pictures to photoshop, they are at 72 dpi. My 4.0MP canon G2 uploads them at 300dpi. Is there a reason it's doing this? I think my brothers 350D does the same (72 dpi).

I've been resizing them to 300 dpi. Would it be making a difference to the quality of the pic or am I wasting my time?
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Old Jan 5, 2006, 4:23 AM   #2
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ViS, A very frequent question & no cause for concern.

The DPI settings you see have no relation to the quality of the camera image. It is just a setting that can be changed in photo editing or printing software, so as to determine the output or print size. It has no bearing on the screen quality or size. This is determined by your monitor resolution.

The real measure of the camera resolution is the megapixels. i.e. pixels across x pixels down. The more the better.

DPI does have a bearing on a photo print size & quality. e.g. say your image is 2400 pixels wide. Using photo editing or printing software, if you select an 8" wide print, the resulting print dpi will be 300, which is excellent. Selecting a 12" print gives a 200dpi print, which is still accepable, but you dont want much less for a good print.

Dont worry about those dpi properties you see. They are not a function of camera resolution or quality.

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Old Jan 5, 2006, 9:18 AM   #3
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That answer is exactly correct ..I only wanted to add that its the software you use to upload to your computer that decides what dpi you upload at, some are able to be set at the dpi you prefer. hunt in the preferences of your program.

But it makes no difference in how the photo appears on your monitor.
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Old Jan 5, 2006, 12:13 PM   #4
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the whole issue of what constitutes acceptable resolution for printing could occupy a thread all its own, but my personal experience, based on a boatload of 8x10 and larger prints from my FZ20, is that 200ppi (pixels per inch) is a good working "target resolution". above that, your eye cannot tell the difference, much below it, and you riskpoor print quality. i've made a few prints at 150ppi that came out okay,and somethat were visibly grainy or "jaggy"; i have others at about 175ppi that were just fine. but i've never been able to detect any improvementonce resolution climbs above200ppi, and i have prints from my FZ20 made at 200ppi that absolutely blow away anything i ever shot with film. of course, all this is very subjective, as each person's eyes are different, and some folks may be able to tell a difference wherei can't, or vice versa. but 200 pixels per inchseems to be the generally accepted minimum standard resolution for a photo-quality print. in theory, your FZ30 should yield images sufficient to make a 12x16 print at 200ppi at its native 8MP resolution. in reality, i can get wonderfully clear, sharp11x14 prints from my 5MP FZ20 with no upsizing, so i would expect you couldget good 16x20 prints from the '30 with minimal risk of print quality problems.

"dpi", on the other hand, refers only to the resolution theprinter is capable of, and is completely independent of the camera. commercial photo finishers useprinters that typically run at 300dpi, which is why i send anythingi want printed to them. every print they make absolutely maximizes the resolution ofmy image. anymore, there are enough cheap online photo printing houses that it's not even a contest... they offer better prints, and lower overall costs than anything i could do at home, and i never have to worry if the printer or my software is set correctly.
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Old Jan 5, 2006, 2:17 PM   #5
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Thanks for the replies.

The thing that bugged me (and what I'm still not sure I understand completely) is that if a picture appears on my screen at 72 dpi straight from the camera, if I then save it at 300 dpi, where is the extra info coming from? In my mind I see 72 little dots filling a square inch and if I change the setting to 300 dpi, all of a sudden there are 300 dots filling that same space, and I don't know how photoshop managed to add all that extra info if it wasn't there in the frst place :-)

From what I understand of your explanation, a picture in 72 dpi would have to be 4 times as large (in megapixels) as the same picture saved in 300 dpi to achieve the same print quality? And I'd be right in assuming that there isn't a change in the number of dots contained per square inch, but it just makes those dots bigger or smaller to alter the overall size of the picture (meaning the larger the pic, the better quality the print)?

I notice when I resize it to 6"x 4", the pixel count drops dramatically until I boost the resolution slider to 300 dpi, where it almost goes back to the original size on the screen.

Anyway, it's certainly given me a bit more food for thought. I'm just glad it's not affecting the quality of the print .

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Old Jan 5, 2006, 4:16 PM   #6
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you're still confusing printer dpi, which is the default print setting in your software, with image resolution, which is something else entirely. you can probably change the printer resolution, and if you're planning on making prints at home, you should set that default as high as it will go. but image resolution is another matter completely.

look at your image on the screen.i don't know what image viewer you use, but you should be able to determine the actual pixel count. that is what's important. if you took a pic with your FZ30 at full resolution (3320x2240 or some such thing), and want to know what print size you can make with that, simply devide those numbers by the minimum pixel-per-inch count you want (see my earlier post) to get the maximumsize print you can get.

ignore the 72dpi number. it has nothing to do with your image resolution, either in the camera or on your monitor. also, don't confuse size on the screen with print resolution or image quality. what matters is pixels per inch. if you have at least 200ppi in any print size you select (for an 8x10, that means an image file size of at least 1600x2000), and use a good photo-quality printer, you will get a good result.
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Old Jan 6, 2006, 1:52 AM   #7
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This is a marvellous Forum. The thread and replies were very instructive and I for one have learned a lot.

I have not confused dpi with ppi but Squirl, you have certainly cleared thing up and I have printed this page for reference

Fred
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Old Jan 6, 2006, 2:23 AM   #8
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look at it this way.....your monitor is gonna see 72 dpi.
Lets take a 1" square image and make it different dpi.

Using 75dpi, 1" sq........monitor sees 1" sq
Using 150 dpi, 1" sq.....monitor sees 2" sq image
Using 300 dpi, 1" sq.....monitor sees 4" sq image

These are all 1" sq images that will "view" at different sizes
Vis, hope this makes a little sense

A 20" long image of 72dpi can print 10" long at 150dpi
or 5" long at 300dpi....I think I have that right


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Old Jan 6, 2006, 8:21 PM   #9
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Are you wondering Squirl, if some here have not read or understood the advice given?

The poster was concerned about the effects of DPI on pic quality.

You said: ignore the 72dpi number. it has nothing to do with your image resolution, either in the camera or on your monitor. also, don't confuse size on the screen with print resolution.

Genece said: But it makes no difference in how the photo appears on your monitor.

I said: It has no bearing on the screen quality or size. This is determined by your monitor resolution.

Yet now we hear that maybe pixels get bigger! And DPI settings change "square inchs" on the screen!

Maybe some are getting confused with resizing. But that's another subject.
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Old Jan 6, 2006, 8:50 PM   #10
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Baz and Squirl were both accurate. Dave in LA was correct in pointing out that the same image printed at a higher dpi will print at a smaller size, but he was incorrect in saying that it affected the way it displays on the monitor.

Let me clear this up:

You have an image, it is 100 x 100 pixels, and 200 dpi.

When you open this file in an image editing program, it displays 100 pixels by 100 pixels. It does not care what the dpi is. It could be 72, 7200, 7, it doesn't matter. The only thing the monitor sees is 100 pixels by 100 pixels.

When you send the file to print however, that dpi setting tells the printer how many pixels to put in each inch. So, that image at 200 dpi will print 200 dots per inch, and therefore be 1/2" by 1/2" when printed.

If you resize it in Photoshop, there are two ways to do so. If you change the dpi while "resample" is selected, Photoshop will change the number of pixels to ensure that it still prints at the same size on paper. So, if I resize it to 100 dpi, it has to cut the pixels down to 50 x 50 so that it still prints 1/2" x 1/2".

If you turn off "resample", then when you change it to 100 dpi, the pixels will not be affected, but your printout will be 1" x 1".

When you resample an image to make it bigger, the added pixels are just interpolated, meaning that if you make it 200 x 200 pixels, Photoshop spreads the pixels apart and then creates new pixels between the existing pixels by blending the nearby pixel colors together (that's a simplistic way of explaining it).

So basically, you can enlarge an image and it will get blurrier when viewed up close on the monitor, but it can smooth out the apparent pixelization. This way, if you have an image that prints 5" x 5" at 100 dpi and it looks too jagged on paper, you can resample it too 300 dpi, and while it won't add any actual detail, it can make it look much smoother when printed.

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