Pixels per inch on Drebel images

[Riod]

I just noticed that my Drebel records at 180 pixels per inch at the finest jpeg level.

My Kodak DC-4800 records at 230 pixels per inch.

Is there a setting on the Drebel that would allow the ppi to be changed?

[dphoto]

Hello Riod,

ppi (also called dpi) can be somewhat misleading. If your camera records 6 million pixels, then it records 6 million pixels. If you take a picture with your 300D at the finest jpeg level, then it will record 3072x2048 pixels. Let's say you wanted to print this image. At 180 ppi, it would be 3072/180 = 17 inches wide. At 300 ppi it would be just over 10 inches wide. At 90 ppi it would be over 34 inches wide. Note the the 90 ppi image is much larger than the 300 ppi, but of course it will be much blockier looking. In either case, we are still using the 3072x2048 pixes. So, the camera could have recorded 90 ppi or 300 ppi with the image, and it wouldn't change the fact that we still have 3072x2048 pixels that we can later choose to print 10 inches wide or 34 inches wide (or however wide you want). So, as you can see, ppi has to do with the printing/viewing of the image, not with the recording of the image. The image was recorded at 3072x2048 no matter what the ppi is recorded as. Why Canon chooses 180 ppi, I don't know. Maybe they felt it was a good usable number.

Play around with the ppi numbers in photoshop under Image->Image Size.
And of course, if you have any more questions, feel free to ask. :)

-Deva

[Riod]

Dphoto ---- Thanks for the reply. I think I understand the ppi/image prrint size as you have explained it. I was just curious as to why Canon chose to use 180 PPI and Kodak chose 230 PPI. The reason I ask is the Kodak is a 3mp machine and the Drebel is a 6 MP machine. I guess I expected that since the Drebel had more megapixels, it would save at a higher PPI resolution.

I have to sit and think about this a bit more!!!

Thanks again.

[Yarin]

I've also got a question?

Someone told me to up the ppi to 300 before printing any image from photoshop. Is this correct?

So I take my original which is 3072x2048, ~17x11 and 180ppi.
Then crop/reduce the document size to 8.5x11 or whatever is desired and up the resolution to 300ppi? Will this yield better quality prints then leaving the resolution at 300? Thanks

Lastly.. the ideal resolution for screen/web viewing without zoom capbilities is 72ppi. correct?

Thanks

[dphoto]

Hehe... OK, no prob. You know, I was wondering that as well. Why 180? I usually change it to 300. But then, why do I do that? I have to think about that some more too. If you find anything out, would you mind posting it here?

Thanks!
-Deva

[dphoto]

Hey Yarin,

Out of habit, I find myself converting to 300 ppi before I print as well. I'm not sure if that's better... I intend to do some experimenting myself... when I get done with some other experiments. :) At some point some interpolation has to be done. If your printer prints at 1200 ppi, and you send it a 300 ppi image, then it's going to add 3 of its own pixels for every 1 you provide. I often wondered if it would be better to use a 1200 ppi image in photoshop and send it to the printer. I guess it would depend upon who does better interpolation... photoshop or the printer driver. But image trying to work with a 1200 ppi image... that could get very cumbersome. If the results are close, I'd choose to let the printer do the interpolation. :)

As for your last question, I'm not sure what you mean by "ideal resolution" for viewing. I'm not sure that there is an ideal resolution... people have different monitor sizes set to different screen resolutions, so it varies from person to person. But most people are probably somewhere in the 72-96 range. But certainly not everyone.

-Deva

[Yarin]

Thanks Dave...

I have a Canon i850, someday i'll buy a i9100. I've got some 13x19" photo paper mocking me.

I mean ideal ppi for screen viewing. Most people resize shots for web to 800x600 or 640x480. I guess it depends on your target audiece. I suppose it is fair to say that people who are oriented towards graphic editing and photo work aren't likely to use a lower screen resolution, ie: <1024x768. 1280x1024 or 1600x1200 seem to be the default for a 17"+ monitor these days.

Cheers.

[jrm]

Canon probably picked 180ppi as a setting simply because for most home printing use this is a perfectly acceptable "consumer" resolution.

As has been explained, the number of pixels "recorded" by the camera is a fixed amount... the "ppi" number is just a way to express the size to display/print the image at - it has no bearing on the actual "resolution" of the image. The "resolution" is simply the number of pixels (width x height).

Where 300ppi is considered a "standard" resolution is in 4/color printing, not home photo printing. However, in 4/color printing the images need to be converted to CMYK format anyway, so post-processing is required.

The 180ppi setting probably also makes it easier to crate an interface to plug the camera directly into the printer (as some Canon models do). By have 180dpi as the standard setting, it probably makes it easier to print out a reasonable size from most cameras.

Specifiying a higher ppi for the same image simpy reduces it's size. A 1000x1000 image at 100ppi is 10" x 10". The same image at 500ppi is 2" x 2". Same information, displayed in a different way.

Now PhotoShop "resolution" conversion can work two different ways. It all depends if you have "resample" checked.

With resample off, you image will have the same exact amount of pixels when you are done (And file size will stay the same). You are just altering the "dimensions" of the image by telling it to change how it dsiplays the pixels (put them closer together and display more pixels in every inch of space, or space them out more, displaying less pixels in each inch of space... thus changing the "pixels [displayed] per inch."

If "resample" is checked, then you are asking PhotoShop to actually create more pixels (assuming you are increasing resolution). While is does this well (within limits) the "new" pixels were NOT present in the original graphic and PhotoShop is simply "guessing" at what these new pixels should contain.

Hope this helps. I deal with this issue on a regualr basis... you would be surprised at how many people involved with professional graphics do not fully understand the concept.

[robertwgross]

This will shock a few people, but of the thousands of images that I have shot with my D60 and printed out, I've used DPI of the image and Size of the print absolutely ZERO. Image DPI is something of no interest to me.

I've always shot RAW files and converted to TIF, so the files tend to be 18 or 36 MB each. I print to fill the size of the paper, which is typically around 8x10 or 11x14 inches, so there are plenty of bits of image to use.

---Bob Gross---

[maderito]

This will shock a few people, but of the thousands of images that I have shot with my D60 and printed out, I've used DPI of the image and Size of the print absolutely ZERO. Image DPI is something of no interest to me.

I've always shot RAW files and converted to TIF, so the files tend to be 18 or 36 MB each. I print to fill the size of the paper, which is typically around 8x10 or 11x14 inches, so there are plenty of bits of image to use.

---Bob Gross---
If you always shoot perfectly composed images, then you can "fill the paper" because you can get acceptable prints when printed from 180 to 300 ppi.

2048 X 3072 pixels = 6.3 MP image
TIF image file size: 18 MB (8 bit) or 36 MB (16 bit)

Print dimension (approx)
180 ppi: 11 x 17 inches
240 ppi: 8.5 x 13
300 ppi: 7 x 10

Some of us ocassionally crop our images - say by 50% in both dimensions giving us an image 25% of the original size (and a 25% smaller Tiff image). Now we can't fill the paper:

1024 X 1536 pixels = 1.6 MP image
TIF image file size: 4.5 MB (8 bit) or 9 MB (16 bit)

Printed image dimensions
180 ppi: 5.5 x 8.5 inches
240 ppi: 4.25 x 6.5
300 ppi: 3.5 x 5.0

Of course, we could upsample that cropped image back to 2048 X 3072. But even with the best upsampling technique or software, someone on the Forum would spot the deception by close examination of the print.

But I like the idea. I think I'll start upsizing all my cropped images to as close to 2048 X 3072 as possible, and thus appear to have taken nothing but perfectly composed shots - saved for eternity as 18 MB or 36 MB TIF files. 8)

Thanks Bob. :D

[robertwgross]

If you always shoot perfectly composed images, then you can "fill the paper" because you can get acceptable prints when printed from 180 to 300 ppi.


"If..."

What do you mean, "If"?

Actually, it is rare for me to crop off more than a thin edge of the original image in order to make it fit better to the paper size. Part of that comes from using zoom lenses instead of prime lenses.

"If..." ?

---Bob Gross---

[boBquincy]

Afaik the camera does not assign a dpi to the image, that is done in the imaging software you use. The camera deals only in pixels.

I use 200 dpi for everyday prints, 300 dpi for fine prints. There is a small difference (on my HP1220 and Canon S9000). Afaik a higher resolution will do nothing but increase file size, print quality will not improve beyond 300 dpi.

I agree with Robert Gross (although I am not always as observant as I should be), if you practice your craft well then no cropping should be necessary. We have an accurate viewfinder, zoom lenses, and feet. Between those we should be able to get exactly the image we want.


boB

[KennyG]

I just noticed that my Drebel records at 180 pixels per inch at the finest jpeg level.

My Kodak DC-4800 records at 230 pixels per inch.

Is there a setting on the Drebel that would allow the ppi to be changed?

This is a very old chestnut. The DPI setting is absolutely meaningless. You can have any number you want in there, it serves no purpose, in fact most cameras use 72dpi for the number. Trust me, your DR records a higher resolution image than the Kodak.

Why are so many people worrying about setting dpi in PS etc. for print outs? The simple answer is to get Q Image and let it manage everything for you. Forget about dpi setting in PS or other editing software, just post-process and print from Q Image. It will color manage and do any required interpolations. If you want to save yourself time and effort as well as get great prints, give it a whirl.

[Ikinaa]

Hey Yarin,

Out of habit, I find myself converting to 300 ppi before I print as well. I'm not sure if that's better... I intend to do some experimenting myself... when I get done with some other experiments. :) At some point some interpolation has to be done. If your printer prints at 1200 ppi, and you send it a 300 ppi image, then it's going to add 3 of its own pixels for every 1 you provide. I often wondered if it would be better to use a 1200 ppi image in photoshop and send it to the printer. I guess it would depend upon who does better interpolation... photoshop or the printer driver. But image trying to work with a 1200 ppi image... that could get very cumbersome. If the results are close, I'd choose to let the printer do the interpolation. :)

As for your last question, I'm not sure what you mean by "ideal resolution" for viewing. I'm not sure that there is an ideal resolution... people have different monitor sizes set to different screen resolutions, so it varies from person to person. But most people are probably somewhere in the 72-96 range. But certainly not everyone.

-Deva

I think here's some misunderstanding between ppi, dpi, printer resolution, camera resolution :

If your printer has a resolution of 2400 dpi, that means, that the printer can print 2400 dots on a line of one inch long, but most printers have 4 colors only... So how does the printer produce these millions of colors?
By putting different pixels with different colors very near so that they melt for your eye to one color.
Take a newspaper, choose a color or bw picture in it, take a magnifying glass and look how greys and colors are done.
For standard news paper, the printing resolution is 1200 dpi, for magazine it's normally 2400 (and it works almost exactly like your printer)
So to put it simply : to have a grey tone in the standard range from 0 to 255, you need 256 combinations of pixels, lets say a square of 8x8 pixels.
The more pixels in this square are black, the darker is the grey-dot.
so if you print at 2400 dpi (printer resolution), you get a 2400/8=300 dpi grey resolution
so if you print at 1200 dpi (printer resolution), you get a 1200/8=150 dpi grey resolution
same with colors
Normally for printing in newspapers or magazines, people don't use 8x8 squares but other patterns which are turned by a certain degree in function of the color printed, so the image appears finer.
Conclusion: to print a photo on a 2400 dpi printer, make sure you got approx 300 dpi as physical resolution of the picture -> to print a picture of 3x4 inch, you'll need a picture of 900x1200 pixels (this should be enough)
More is better, but less is worse.
So if you know all this or not, is relatively meaningless, except perhaps for calculating the size you can print your photo without losing too much quality

[maderito]

If you always shoot perfectly composed images, then you can "fill the paper" because you can get acceptable prints when printed from 180 to 300 ppi.


"If..."

What do you mean, "If"?

Actually, it is rare for me to crop off more than a thin edge of the original image in order to make it fit better to the paper size. Part of that comes from using zoom lenses instead of prime lenses.

"If..." ?

---Bob Gross---
The main point of my previous post was to show the relationship of resolution, image size, and file size - in keeping with the thread's subject.

But I chose your post (which mentioned file sizes) to also raise once again the never-ending discussion about cropping. I think we all aim to shoot perfectly composed images. But I often fail - sometimes from lack of experience, other times because the subject matter is just too fast moving, and naturally when the 3:2 aspect ratio is not suitable to my final enlargement.

My fun with digital photography - for bettter or worse - is to find that there are often shots within the shot. With 6.3 megapixels, you have plenty of image bits to work with. And so I'm not afraid to crop even a well composed shot - say an informal portrait. I might lop off part of hair/head/shoulders in order to create a new and interesting perspective. The next time I shoot a similar portrait, I might try to create a full frame version of that cropped perspective. Thus I learn by cropping.

I didn't mean to hijack this thread in order to discuss an old (and perhaps tiresome) subject. However, thanks for confirming that you are part of the "do not crop" school of photography.

I remain your humble student. :)

[CyberDyneSystems]

Afaik the camera does not assign a dpi to the image, that is done in the imaging software you use. The camera deals only in pixels.

I use 200 dpi for everyday prints, 300 dpi for fine prints. There is a small difference (on my HP1220 and Canon S9000). Afaik a higher resolution will do nothing but increase file size, print quality will not improve beyond 300 dpi.

I agree with Robert Gross (although I am not always as observant as I should be), if you practice your craft well then no cropping should be necessary. We have an accurate viewfinder, zoom lenses, and feet. Between those we should be able to get exactly the image we want.


boB

Bob quincy is correct,. the ppi number of 180 is meaningess and has no bearing on the Camera image whatsoever,. I truly doubt the 180ppi info is embedded in the image,. rather that is a default that the software is choosing? (I could be wrong) but either way,. it is an arbitrary number that means nothing untill you print. And of curse by altering this number in the printing stage,. you do not alter the image itself at all, the actaul number of pixels does not change.

[dphoto]

Oh, Ikinaa's right. I forgot, different colored pixels are layed right next to each other in print. So if you have a 1200 dpi (before any printer interpolation) printer with 6 colors, then does this mean a 200 dpi image would be as much resolution as you would need to get the most from the printer? As for a 1440 dpi printer, that means a 240 dpi image.

As for the 300D, even though it does not affect your image quality in any way (you captured 6 million pixels no matter what), 180 dpi is embedded in the EXIF info. XResolution is set to 180 and ResolutionUnit is set to 1 inch, hence 180 pixels per 1 inch.

boBquincy, you said that you see an improvement with 300dpi over 200dpi with your S9000. Can anyone account for this? Maybe since the printer is going to interpolate to 2400 dpi, it can do a better job with more dpi? So would 400 dpi be to absolute maximum you would ever need on that printer? boBquincy, have you tried printing at 400 dpi? Maybe in theory it would be better, but not in practice? Ugh, I'm horrible with the "eye test". :)

-Deva

[Pekka]

I deal with this issue on a regualr basis... you would be surprised at how many people involved with professional graphics do not fully understand the concept.

I've learned it is futile to fight the cluelessness of many AD's and press buyers. Just do what they want and don't make a big deal out of it:

Just recently I delivered some CD cover photos to one (big/international) record company. After a while I got a message that their AD is wondering why the photos are 72 dpi; they look just great but they were insecure of how printing quality would be so they would require higher dpi. I changed the dpi to 300 (nothing else) and gave them new files and they were happy. :)

[dphoto]

HA! Classic. Well, as long as you know what you are doing, you can always make it "right" for your customers. :)

-Deva

[jrm]

Pekka,

Heh, I feel your pain.

I, unfortunately, am on the other side of it. My "output" goes to printing companies that expect everything "right." (Or they will happily bill me for the corrections.)

My "input" is sometime from people that don't understand resolution. Clients that do not know where to get product art, for example, figure they can sent me "images from our web page." These 2"x2" 72ppi jpegs do not work well as 5"x7" images on a printing press.

Once, I explained to a client that they has to send me 300dpi images at 100%. They explained that that was easy - they had PhotoShop and just had to resize the image. You can imagine the result. Since then, I stopped asking for specific formats/sizes (unless I am dealing with people who know the difference) and just ask a lot of questions about the origin of their artwork.

[Ikinaa]

Oh, Ikinaa's right. I forgot, different colored pixels are layed right next to each other in print. So if you have a 1200 dpi (before any printer interpolation) printer with 6 colors, then does this mean a 200 dpi image would be as much resolution as you would need to get the most from the printer? As for a 1440 dpi printer, that means a 240 dpi image.

As for the 300D, even though it does not affect your image quality in any way (you captured 6 million pixels no matter what), 180 dpi is embedded in the EXIF info. XResolution is set to 180 and ResolutionUnit is set to 1 inch, hence 180 pixels per 1 inch.

boBquincy, you said that you see an improvement with 300dpi over 200dpi with your S9000. Can anyone account for this? Maybe since the printer is going to interpolate to 2400 dpi, it can do a better job with more dpi? So would 400 dpi be to absolute maximum you would ever need on that printer? boBquincy, have you tried printing at 400 dpi? Maybe in theory it would be better, but not in practice? Ugh, I'm horrible with the "eye test". :)

-Deva

The printers with more than 4 (CMYK) colors have variations of these colors in the other cartridges, one printer has pastel colors, the other has different grey tones. In fact, I believe they're not used for a better resolution but for a better color representation, with more natural colors and more tones.
So if you got a printer who has light gray, dark gray and black, you get a much more natural BW picture than with black only.
As for the pastel tone, with the standard CMY, you can't get a real pastel tone, but with pastel CMY, the pictures will look more natural.

One thing I forgot in my previous post:
There are termo-subliminal-printers: these printers often have a resolution of ... 300 dpi . No don't laugh at this small resolution... these dpi are different from the dpi of the inkjet. One dot from these printers can have one of 256C * 256M * 256Y * 256K = 4294967296 (theoretical) colors in opposition to the 4 different colors of one dot from the inkjet.
These printers used some plastic film with the 4 colors and with the heat transfer a part of the dot to the (special) paper, and that 4 times, so one dot from the picture file is one dot on the paper...