Sizing photos using resolution

[cats4jan]

I decided to try resolution as a means to change the size of the 144 ppi 17x13 photos that came off my camera.

I changed the resolution to 300 because that's what my scrapbook page was.

I know merely transferring them to the 300 ppi page would have automatically resized them, but I wanted to crop and do other things prior to moving them onto my scrapbook page.

When downsizing, is there any benefit to having "resample image" chosen?

Is what Elements does when resolution changes the size any different than if I had a 300 ppi image - moved it to a 300 ppi project - and used the bounding box to downsize the photo?

I assume if I was trying to make the photo larger, I would choose "resample image" (knowing it would not necessarily be a great enlargement no matter whether resample was on or not.)

I'm just learning resolution affect on size - am I over thinking this?

[Codebreaker]

First important thing to remember - your camera does not deliver a physical size image. It only gives you a number of Pixels. What physical size this ends up is entirely up to you when you come to assign a Resolution to it - i.e you use a specific PPI setting.

Your documents don't have a PPI setting, really - just Pixels and if you move an image from one to another then one Pixel in one image still only takes up one Pixel in the other.

So, for instance you have an image of 3000 x 2000 Pixels and another of 1500 x 1000 Pixels. If you move the smaller to the larger it just appears smaller in comparison to the original because it has less Pixels.

If you re-sample an image you alter the number of Pixels. This is an artificial process as Photoshop has to either create additional pixels or remove some pixels and then alter the one's left to make the image appear OK. Over do this and you can produce poor quality results.

Where the resolution comes in is where you decide the image needs to be a specific Physical Size.

If you change the Image Size using the Image > Resize > Image Size command you should always try and get the Physical Size you need without Re-sampling checked. In this case for printing you need to keep the resolution greater than 200PPI (ideally greater than the magic 300PPI). If you can't then you have to turn it on.

If you use Transform or the Move Tool to re-size then you automatically re-sample - which, again if overdone can be bad.

Colin

[cats4jan]

Because I've been reading up on pixel vs resolution vs physical size on this forum - I think I have a good understanding - i.e., an image comes out of a camera a certain pixel size and resolution determines the physical size of the photo.

And when changing resolution - avoid resampling.


If you use Transform or the Move Tool to re-size then you automatically re-sample - which, again if overdone can be bad.


Thanks - that was an important piece of information.

I use 300 ppi for my resolution when I'm planning to print.

Here's the dumb question of the day.

If I'm doing something really small - and I want to print it - is there a downside to sending it to the printer - say - at 900 resolution?

I do understand that that resolution and the number of dots of ink my printer puts down on paper are two different issues.

[swalkr]

Because I've been reading up on pixel vs resolution vs physical size on this forum - I think I have a good understanding - i.e., an image comes out of a camera a certain pixel size and resolution determines the physical size of the photo.

And when changing resolution - avoid resampling.

Thanks - that was an important piece of information.

I use 300 ppi for my resolution when I'm planning to print.

Here's the dumb question of the day.

If I'm doing something really small - and I want to print it - is there a downside to sending it to the printer - say - at 900 resolution?

I do understand that that resolution and the number of dots of ink my printer puts down on paper are two different issues.

Okay, here's a dumb question from me: What is the difference between dpi and ppi and resolution? That has stumped me for a long time.

[cats4jan]

Here's my understanding -

Experts? Correct me if I'm wrong


An image is made up of colored squares - specified by ppi - pixels per inch -

Resolution determines the physical size of your photo

A image that is 1200 by 1200 pixels per inch

---when divided by 300 resolution

will give you a photo that is 4 inches by 4 inches

---when divided by 100 resolution

will give you a photo that is 12 inches by 12 inches

This resolution issue is why - when you move a photo or graphic with one resolution - to a project with a different resolution - the size of the photo or graphic changes sizes.


dpi - dots per inch - is the number of dots of ink that your printer lays down on a page.

[TonyW]

Janice - that sounds pretty close. I would quibble though with an image being made up of dots. Screen pixels and Printer dots are very different. On the screen one pixel contains all the information about colour and isn't really a dot - it's a small coloured square. Zoom right in one the screen and you can see them. Printer dots really are dots and they can are only one colour - the colour of the ink. The printer puts a bunch of different colour ink dots together in an attempt to fool the eye into seeing the colour of one pixel. So it takes many printer dots to represent one pixel. But it can only put down so many dots in an inch. So up to a point the more pixels per inch improves picture quality but having more doesn't make it better because the limitation becomes the printer and the paper (a small dot gets bigger when it hits the paper and spreads). What the optimum pixels per inch is somewhat controversial. Some say 300, some say 240, others say above 200 you can't tell the difference unless you get out a microscope and who uses a microscope to look at pictures :).

The sad thing is that marketing just confuses the consumer. Printers promote resolution and quote big dpi numbers - but it take lots of dots to represent a pixel so you can't compare the two. And just because a printer could give you a very high dpi doesn't mean it does because of the paper effect. (Print on ordinary paper and an image at 50 ppi will look OK - just not good - and higher resolution won't make it look any better)

PS (for the technically inclined :)) The word pixel comes from Picture Element - and technically it doesn't have any shape - it'd the smallest part of an image that can represent the right colour and colour intensity.

Tony

[cats4jan]

I knew they were squares - done enough zooming to know that - just didn't remember. LOL

The technical concept of resolution and printing will never get across to those of us technically challenged.

Although my explanation is not precise - I hope it gives an inkling to those who are confused by ppi and dpi - if only an inkling. And I hope it's correct enough that I'm not giving out incorrect information.

I'm changing the word dots to squares - don't know if that will help make me more correct.

Everytime someone explains this to me - I am absorbing more of the technical aspects of the concept.

I appreciate your patience in continually having to explain this to us. It's really hard. That's all there is to it.

I'm just glad that now I know why things change sizes when I move from project to project.

[swalkr]

Janice & Tony, those are good explanations for me. I understand it better. Now, to add to the other part of the equation, how does camera megapixels figure in with ppi?

[Chuck S.]

Suzanne, the megapixels are found by multiplying the width of your image in pixels by its height in pixels. For example, an image that is 3000 pixels wide by 2000 pixels high would contain 3000x2000=6,000,000 pixels - six million pixels. "Mega" means "million", so that image is 6 megapixels.

The resolution in ppi (pixels per inch) really has no meaning until you go to print. But if I took the image above and wanted to print it at 100 ppi (not a good idea, but it makes the math easier!), the print would be 3000 pixels/100 ppi =30 inches wide by 2000/100=20 inches high.

[Codebreaker]

Just to add to the over whelming amount of information.... :)

The Pixels on your screen are not really square. Each Pixel is made up from sub-pixels, one for each of Red, Green and Blue. It could be argued therefore that screen pixels are tri-angular :confused:

The term PPI and DPI are regretably used interchangeably today. Even Photoshop mixes the terms. The history is that DPI comes from the old printing technolgoy when images were made of Dots.

Camera manufacturers mislead people into thinking there camera can produce large physical images. The data from the camera includes a DPI setting - but this is a recommendation only. Some manufacturers don't include a number and the default becomes the famous 72DPI.

As for sending higher resolution e.g 900PPI images to a printer - well again all your sending is Pixels and asking the printer to fit them into the Physical size you've asked for. Some printers are OK with large numbers others not. My ancient Canon i850 gave problems when I used 1024.

Colin

[msbrad]

I'm hanging onto this thread. I'm understanding better and better.
Thanks all for helping me 'see the picture'
m

[cats4jan]

Tri-angular? I give up. :D

When looking for a camera, how do I find out how much compression the camera will do to write the info to the card?

I'm assuming all cameras compress unless you are using RAW (is TIFF the same as RAW)

I have now set my camera on SHQ - which must compress less because although the pixel size of my image is the same as HQ - the card yielded half as many photos.

(And am I right tht not all cameras use this same terminology - i.e., SHQ, etc.)

I now understand that no matter what settings I'm at - there are only 5 million pixels available to make my photo - so isn't the difference in settings a compression issue?

They are saved in jpg in all formats but RAW and TIFF, right?

(I have the option to save as TIFF - not RAW - but that format uses way too much card space and my photos aren't good enough to warrant using those settings.)

I'm assuming compression means the camera "throws out" pixels to make more photos fit on the card.

I have a 5 mp Olympus Camedia C50 - it's five years old now, but the latest photos I took - using some of the techniques I learned here - turned out better than any others I've taken. I don't know if raising the "saved" settings helped.

[TonyW]

Janice: You're starting to sound more and more like a pixel expert :D. That all sounds right to me. I have found different cameras I've owned have different words for compression settings (I've had HQ/SHQ, Fine/Extra Fine and Normal/Fine I think. And with some cameras I can notice the difference and on some I can't. Camera manuals/specs often will tell you what the compression is. On my D80 Fine is 1:4, Normal is 1:8 and Basic is 1:16 - all numbers approximate as it depends on the image.

Colin: You're right of course :). I was trying to stay simple. Best definition I've seen is the wiki one: A pixel is a single point in a graphic image. Each such information element is not really a dot, nor a square, (nor a triangle) but an abstract sample. ;). And then there are sub pixels, dead pixels and stuck pixels but let's not go there :D

Tony

[Wendy]

Hi Janice ...

When you save at the best settings you get the most pixels ... so thats the way to go.

Compression ... well its how the camera does it and I doubt that you will see any deterioration because of it. Don't get too bothered by this ... as long as you get a good camera then the images from it will be good. I save as jpg except on the rare occasion I decide to shoot in Raw ...

(Hey what is behind the camera takes the pictures ... and any good quality camera will capture them)

Wendy

[cats4jan]

And don't leave the gremlins out of the equation

They are my most dreaded enemy - they put fingers and camera straps into my photos - they make shadows - they even take photos of the ground sometimes.

[Codebreaker]

The camera sensor has a fixed number of Pixels. There are two options usually available to determine the file size that gets stored on your memory card.

1. JPEG compression - in this process the Pixel Dimensions of the image remain the same but the amount of information is compressed at the cost of image quality - more compression, lower quality, smaller prints.

2. Re-sampling and JPEG Compression - in this process the Pixel Dimensions get reduced and the image undergoes compression - less Pixels, smaller prints.

The compression scheme doesn't through away Pixels - it throws away some of the colour information because our eyes are not so sensitive to changes of colour but more sensitive to tones of black and white. So the process reduces the amount of data needed to 'playback' the scene. It's the imaging equivalent of MP3.

There really is no point, in my opinion, of setting your camera to anything less than the absolute, best, really fine, top notch, grade-a quality and Pixel dimensions. The only one time to do this is if you are really running low on memory card space and simply must get the shots. (Remember you can change these settings at any time on a shot by shot basis if you must)

If you consistenly use lower settings then you should really have got a lower spec. camera - I'm not for one minute suggesting this is the case though, just as information for anyone else listening in.

If you want to really blow your mind with how many Pixels a camera has take a look at the Sigma Foveon sensor and work out how many that has compared with what they advertise - the SD14 I think the camera's called.

Colin

[Chuck S.]

There really is no point, in my opinion, of setting your camera to anything less than the absolute, best, really fine, top notch, grade-a quality and Pixel dimensions.
Colin

Completely agree with Colin on this one and I'd recommend going one step further: if your camera can capture RAW images, choose that option. More work in post-processing, but less reliance on the camera's simple mind to do the initial JPEG compression, sharpening, saturation, and contrast. Fortunately, ACR has gotten easier to use and more full-featured than its predecessors; it's actually fun to use now.

[Codebreaker]

And I would agree with you, Chuck. :)

[cats4jan]

Is TIFF and RAW the same thing?

[Chuck S.]

Janice, RAW and TIFF aren't the same thing. RAW is, as it sounds, pretty much an unprocessed capture of what hits the camera sensor when you snap the shutter. It requires post-processing to turn it into a visible image, but it has a minimum of in-camera processing before it's saved to the memory card, i.e, no sharpening, contrast, or saturation adjustments, and only 'lossless' compression. RAW images tend to be 2 or 3 times as large as a JPEG, depending on the amount of compression to which the JPEG is subjected in-camer

TIFF, on the other hand, is an image format that's lossless, as opposed to the lossy JPEG format. TIFF images are subject to the camera's processing before being saved, and their biggest drawback is their size: maybe 8-10 times as large as a JPEG. I think if I had a choice between saving super high-quality JPEG and TIFF, I might be tempted to stick with JPEG just because of the size issue (chews up a lot of memory card space and may, on some cameras, take a noticeably longer time to save).

I probably have a few of the facts garbled here, so I hope Tony, Colin, Lee, Nick, Gary, Juergen, or one of the other experts will come along to tweak this.

[twoaussies]

I have another question. The photos from my camera come in at 53 by 36 inches at 72ppi. Can I resize all of them at the same time to 300 ppi thus reducing the size? It is time consuming to do them one at a time. Thanks Jean

[TonyW]

Jean: You could (using Process Multiple Files I think) but I wouldn't recommend it and it's not necessary. It's the pixel dimensions that count and that's the same whether they are at 72ppi or at 300ppi (unless you resample). I have cameras that PSE imports from at 72ppi and 150ppi and I only remember very rarely having found a need to change the ppi.

Why were you thinking you needed to change it?

Tony

[cats4jan]

Now I remember - my camera information did mention the very long time it will take for a TIFF to be saved to card. And I noticed you sure couldn't get very many photos on a card in TIFF.

I don't think my camera does RAW - so that's not an issue anyway.

For the novice photographer - TIFF and RAW seem like overkill. I think I'll stick to the next best thing SHQ - it served me well Sunday - for my outdoor and indoor shots - both near and far - and I'm sure it will serve me well the next time.

Thanks for all the information provided here and on my other thread. I've learned alot. I have a much better understanding of the limitations of a typical P&S camera - and the resolution/ppi issue.

[Wendy]

Hi Jean ...

The only time I ever do that is if I want to printout one of them ...

Wendy

[Codebreaker]

Chuck's description of Raw v TIF was spot on. Basically the difference is that Raw you process - TIF the camera processes. RAW can sometimes give you a better opportunity to recover a shot that went wrong but you have to work at it.

A correctly exposed image in the camera can look just as good in JPEG as in RAW - it depends on how 'nit picky' you want to be and how much of a control freak you are.

Colin

[TonyW]

Hi Jean ...

The only time I ever do that is if I want to printout one of them ...

Wendy

Wendy - I don't even bother to change it then. Cropping gets the ratio right and that's all that really matters. Some print shops still specify say a 4x6 at 300ppi but that's not what they really mean. What they mean is that the pixel dimensions should be 1200x1800.

Tony

[Wendy]

Hi Tony ...

Sorry I should have said when I print out myself ... but its good to hear that I wouldn't need to resize if I have them done commercially :)

One of these days I really will have some printed ..

Wendy

[TonyW]

Hi Tony ...

Sorry I should have said when I print out myself

Wendy

I don't bother then either :D. I let Elements and the printer figure it out and they do fine - and having more than enough pixels isn't a problem at least with my printer. But maybe Macs are different ;).

Tony

[Mike_P]

I hope it gives an inkling to those who are confused by ppi and dpi - if only an inkling.

Sorry, can't concentrate on this thread until I stop chuckling over this comment. DPI....inkling.....get it? :D

-- Mike

[Chuck S.]

Basically the difference is that Raw you process - TIF the camera processes. RAW can sometimes give you a better opportunity to recover a shot that went wrong but you have to work at it.

A correctly exposed image in the camera can look just as good in JPEG as in RAW - it depends on how 'nit picky' you want to be and how much of a control freak you are.

Colin

And, for those of you with certain DSLR's, the choice between RAW and JPEG can also be....BOTH. There's a setting that will provide both the RAW image and a JPEG each time the shutter is snapped. Talk about burning through memory cards and computer hard drives.....! I did that for a short while but decided that was taking waffling to the extreme...

[twoaussies]

I am more confused than ever now. I thought that to print a photo it should be 250 ppi or better. I save everything to an "Original" file just as it comes from the memory card. Then on a copy I increase the ppi from 72 to 300 (thus reducing the size to 12 inches and go from jpeg to tiff to work on the photo.
I do want the end result to be print worthy.
Please explain in high school terms. Everyone is so patient. Thanks Jean

[cats4jan]

Quote:
Originally Posted by cats4jan
I hope it gives an inkling to those who are confused by ppi and dpi - if only an inkling.

Sorry, can't concentrate on this thread until I stop chuckling over this comment. DPI....inkling.....get it?

I truly didn't know I was that clever. :D:D:D:D

[cats4jan]

I thought that to print a photo it should be 250 ppi or better. I save everything to an "Original" file just as it comes from the memory card. Then on a copy I increase the ppi from 72 to 300 (thus reducing the size to 12 inches and go from jpeg to tiff to work on the photo.
I do want the end result to be print worthy.
Please explain in high school terms.

Ours is not to reason why...


Now I'm getting confused - I don't have an answer for you - but the experts will.


I just do it. I make my scrapbook pages at 300 and I use resolution to resize my photos to 300 - because...

Scrapbook papers and embellishments come as 300 ppi

Because the projects made at 300 ppi look good when I print them -

and because "the collective - they" have told me to use this resolution LOL

[Chuck S.]

I am more confused than ever now. I thought that to print a photo it should be 250 ppi or better. I save everything to an "Original" file just as it comes from the memory card. Then on a copy I increase the ppi from 72 to 300 (thus reducing the size to 12 inches and go from jpeg to tiff to work on the photo.
I do want the end result to be print worthy.
Please explain in high school terms. Everyone is so patient. Thanks Jean

Jean, you're right: print quality is significantly better at 240/250 ppi or higher. If you're routinely printing your images, going through the process you describe of changing the resolution with resampling unchecked is probably a good way to make sure you don't forget to achieve the target ppi before going to print.

After you take that step, of course, you still have cropping to do to meet the desired size for your print. Having already set the resolution to ppi in your first step, you can simply crop with the crop tool or horizontal marquee tool to achieve your desired linear dimensions, and the resolution will stay at 300. Is that what you've been doing?

[TonyW]

Jean: Sorry to confuse but just to add to what Chuck said here's a simple example (I picked numbers that are easy to work with - and I haven't included any cropping).

A camera takes a picture at 3600x2400 pixels

Downloaded to Elements at 100 ppi Elements would show it being 36"x24"

If I change the resolution without resampling, the number of pixels stays exactly the same which is what you want to do. So my original pixels would show as being:

36"x24" at 100 ppi
12"x8" at 300 ppi
6"x4" at 600 ppi

So if I just send my original pixels to a my printer and tell it to print a 4x6 I'll be sending a 600 ppi image and that is more than enough for printing. It will do that even if Elements still shows it as a 36"x24" at 100 ppi. That's why I don't bother to change it.

Tony

[twoaussies]

By George, I think I've got it. However, when I print I dont tell my printer the size I want - do I????? In the past I have been resizing the photo to what I want it; push Print, and the photo comes up on an 8.5 x 11 page. Then I can move the photo to wherever I want on the page instead of the middle, thus saving photo paper Jean

[TonyW]

Jean: By George - I think you have got it :). I can see that printing that way could make it a bit trickier because a low ppi would look huge to start with and you'd need to change the scale until it fits (which brings down the size and increases the ppi). I almost always crop to a specific size (but with the resolution box unchecked) and then print and then you can do it the way you do it.

And you might not be telling the printer what size you want but Elements is :) - that's what things like the print dialogue box and paper size selection is doing.

BTW if you do happen to get it wrong Elements does warn you if you're going to be printing an image at less than 220 ppi. So if you don't get that warning you know that you have enough pixels for good print quality.

Tony

[Chuck S.]

Tony, were you a teacher in your earlier life? If not, you certainly should have been.....:)

[TonyW]

Chuck: Only for a very short time and in a much earlier life - as a 20 year-old in University I earned some extra cash teaching mathematics to a senior class at an all-girls high school (typically 17 year-olds). Now that was a challenge - and not just the mathematics. :eek:

Tony

[swalkr]

I have another question. The photos from my camera come in at 53 by 36 inches at 72ppi. Can I resize all of them at the same time to 300 ppi thus reducing the size? It is time consuming to do them one at a time. Thanks Jean

I have sent you a PM.

[Kamaditz]

All I can say is WOW! I have just gone along on my ignorant way & done pretty well. Now, I am not so sure and am still confused as to figuring sizing for printing & what is best for a larger picture of 8x10 or larger. Kathy

[TonyW]

I have just gone along on my ignorant way & done pretty well. Kathy

Hi there and welcome to the forum. I think you have exactly the right attitude. If you're doing well then there's nothing to worry about :). The proof of the pudding is in the printing. If it works for you then don't change...

Tony

[RobertSchuldenfrei]

Dear Forum,

I am not sure I should jump in here after all of the very learned members have joined in with some very good advice. However, if you are just starting out and want to keep it simple I suggest doing this:

To print a letter size print from an image that has not been cropped too much go ahead and resize with resampling. Let's assume you have a portrait picture that comes from a 6 MP camera. My Nikon will produce 2000 px by 3008 px. Resize the picture to a width of 8 and the height will default to 12.032. Keep resampling on and set to 300 ppi. After resizing crop the final image to 8 by 10.5. Print on high quality letter sized paper and look at your results. Most of the time your picture will be excellent and you need no further grief.

Now I fully understand that when you resize with resampling you are going to loose picture quality. For a more complex discussion read my next post.

Cheers,

Bob

[RobertSchuldenfrei]

Dear Forum,

I my last post I gave a very simple approach to the print issue. Here is a more detailed justification for my use of resampling.

I have been doing some thinking about resolution and some experiments. Most people will have cameras that are greater than 4 MP. I really don't want to get into the debate about resampling. I understand that whenever you let the program add or subtract pixels you are doing damage to the image, but...

Many people will want to make letter sized prints. If they have cameras that are over 4 MP you can adjust the size and at the same time keep the ppi to a constant. I tried two cameras using two different procedures in order to get an 8 by 10.5 image on a letter sized piece of paper.

First test was my Nikon D70s which has 6 MP arrayed 2000 by 3008. I resized the image without resampling so that I ended up with an 8 by 12.032 image at 250 ppi. I then cropped it to 8 by 10.5 and printed it. No pixel was harmed.

Test two was the same image reduced to 8 by 12.032 with resampling to 300 ppi. I used the Bicubic sampling even though Bicubic Smoother will do a better job. I cropped and printed that picture on my Canon S9000 printer using Ilford Smooth Gloss Gallerie paper.

I could see no difference in print quality even using an 8X loupe. This, for most of us, will be good enough. Let me repeat that I do understand that my first print is better, it is just that I could not see the difference on my equipment.

Then the above test was done with my Olympus C-750 camera which has 4 MP. This leads to an array of 1712 by 2288 which is formatted to 23.778 by 31.778 @ 72 ppi. Using the same procedure as outlined above, I could still see no differences in the two final prints. One was at 214 ppi and no alterations of pixels. The other was 300 ppi with the program adding pixels. Again, I could see no difference with my equipment.

I am not saying that there is no difference, there must be. All I am saying is that for a letter sized print with cameras that are greater than 4 MP it does not matter.

In addition, if your camera is 10 MP or greater and your printer can not handle large ppi, you might actually get a poorer quality print as the translation into printer dpi may make bad decisions. I do not have the equipment to test this, but Rob Sheppard in his book Complete Guide to Digital Printing warns on page 40 about printing above 300 ppi can lead to image degradation.

Why in the world would you want to keep printing at 300 ppi? Janice suggests that when you mix images, letting the ppi vary as it must if you are not going to add or delete pixels, the program does funny things to the output size. Also, most of us have printers that would not do well with ppi values over 300.

My bottom line is that you must test your equipment to see what works for you. One size does not fit all. I hope this is helpful and I trust I have not offended anyone.

Cheers,

Bob

[TonyW]

Just have to add (and at the risk of causing further confusion) that if you happen to have an Epson printer that 360 ppi is better than 300 ppi because that's the native resolution of Epson ink-jets (Canon and HP are 300 ppi). So with my Epson printer and with admittedly a test image and not a real photo I can get sharper images at 180 ppi (half 360) than I can at 300 ppi. But it does need a magnifying glass to see the difference so I wouldn't worry about it because I don't :).

An excellent article on the whole issue can be found here:

http://www.steves-digicams.com/techcorner/January_2005.html

Tony

[cats4jan]

Janice suggests that when you mix images, letting the ppi vary as it must if you are not going to add or delete pixels, the program does funny things to the output size]

Did I say that? I don't think so.

I merely said - that realizing how resolution works explains why if you move a graphic which has a resolution of 300 - onto a project that has a resolution of 150 - the physical size of the graphic will change - it will get twice as big.

I was not talking about ppi's relationship with dpi and printing.

And I merely said - I create at 300 - send those creations to my printer without changing the resolution.

But now? with the information that maybe Epson would work better at 360, I might try 300 and 360. And I might try 180. Just because - I want to see - what I'll get.

[TonyW]

Janice: I like to hear that. When you've got it figured out enough to want to experiment and see for youself - you've got it figured out :D

Tony

[RobertSchuldenfrei]

Did I say that? I don't think so.

I merely said - that realizing how resolution works explains why if you move a graphic which has a resolution of 300 - onto a project that has a resolution of 150 - the physical size of the graphic will change - it will get twice as big.


Hi Janice & Forum,

I should have used quotes like in this post. It was the above resizing of multiple images, as you pointed out, that can add complexity to this issue. Was strictly referring to the ppi topic and not to ppi vs. dpi. To sum it up from my end, we have a simple approach and a more complex approach. A lot depends on your own equipment. I have learned a lot from this, and similar, threads. Thank you Janice, Tony, Colin, and Chuck for your insight into this topic.

I have some more experiments to do with my equipment. I would like to find the lowest resolution I can print at and still not see a degradation in final image. The I would like to test my Canon printer for the highest ppi that I can print without the printer driver making some bad decisions about the conversion from ppi to dpi.

Tony passed on to me in a PM an article by Mike Chaney:

http://www.steves-digicams.com/techcorner/January_2005.html

I have added it to the list of resources on the topic of "resolution." It is interesting to note that as of today, our forum has 500 threads with the keyword "Resolution." I dare say a book could be published from our discussion alone:).

Cheers,

Bob

[Codebreaker]

Bob....

I did some test a couple of years back on my Canon i850. It started giving problems when I had the resolution in excess of 1000PPI. Pixels actually got missed in places i.e. white space appeared.

At the other end viewing distance is an important factor. I've printed as low as 75PPI and you can see the image is not sharp when held close but on a wall at about 6' it would be difficult to tell. I even went as low as 10PPI and that did get very noticeable up close.

I think modern printers are pretty good at producing prints from lowish res. images.

Colin

[TonyW]

I think modern printers are pretty good at producing prints from lowish res. images.

Colin

Colin: I think you're right, even my older Epson R300 does a pretty good job. One thing I've never really experimented with are the quality settings in the printer driver. With my Epson and high quality paper selected there are 5. They don't tell you the difference but I did see a note somewhere (for another Epson printer)that indicated they changed the printer resolution to:

PhotoRPM = 5760 dpi
Best Photo = 2880 dpi
Photo = 1440 dpi
Fine = 720 dpi
Economy = 360 dpi

PhotoRPM appears to be some kind of software driven resolution enhancement as it's above the printer capability. I guess I should run some tests to see the difference these settings make. I also saw a suggestion that icc profiles are done using the Best Photo setting.

Just something else to experiment with ;)

Tony

[Codebreaker]

Certainly for my Epson there are different profiles for each of the settings. I've tried both RPM and Best Photo, but personally I can't see a difference.

Colin

[cats4jan]

Tony - I didn't know that the different settings on my printer changed the resolution. Interesting - makes sense.

That article by Mike Cheney from Steve's Digi-Cams re: ppi/dpi was excellent - Clear and concise and easily understood.

[lisabee]

Thank you all for such an interesting and informative discussion, very helpful,

Lisa :)