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Resampling and Resolution
windoze
Registered Users Posts: 2,830 Major grins
I happened to be doing some reading ( always a dangerous thing for me to do ) and came upon the article with Andy ( http://www.popphoto.com/photonews/4353/get-the-results-you-want-from-online-printing.html ) talking about resolution and stuff like that....
Anyway - my ( limited ) understandingis that when you use photoshop, its best to change the resolution to 300 before sending the file off to be printed. Now when i say change the resolution to 300 pixels im taking into account that Ive "unchecked" resample and the printed size i wanted (4x6) did not come about as of resampling. This is because if you increase the resolution with resample checked photoshop adds pixels to the image - and this supposedly is not a good thing.
Now according to Andy ( in the article ) , its best not to change resolution, just be sure that you upload the biggest file possible even at 72 pixels and the labs at SmugMug will do what they do best.
Until now, primarily because i havent really used CS2, i havent concerned my self with this issue. When ive used my printer - i just select photo from the dialog box on my prnter settings and ive thought it takes care of itself. Now im thinking, am i suppose to change the resolution in the Image Size dialog box from Photoshop?
Questions:
1) if I want to print using my canon i9900 printer, do i concern myself with the resolution? I think that most top notch consumer printers are best when resolution is between 225 - 250 pixels or something like that. How do you know? How do you tell what resolution your printer prints best at and do you indeed make these changes before printing?
2) if you dont use this "magic" resolution number then what happens? for instance, if i find out that i should be changing my resolution in photoshop to 250 before i print and i dont change anything - would it make a difference?
3) so what is good advice for home printing when using photoshop regarding the resolution in the Image Size dialog box?
troy
Anyway - my ( limited ) understandingis that when you use photoshop, its best to change the resolution to 300 before sending the file off to be printed. Now when i say change the resolution to 300 pixels im taking into account that Ive "unchecked" resample and the printed size i wanted (4x6) did not come about as of resampling. This is because if you increase the resolution with resample checked photoshop adds pixels to the image - and this supposedly is not a good thing.
Now according to Andy ( in the article ) , its best not to change resolution, just be sure that you upload the biggest file possible even at 72 pixels and the labs at SmugMug will do what they do best.
Until now, primarily because i havent really used CS2, i havent concerned my self with this issue. When ive used my printer - i just select photo from the dialog box on my prnter settings and ive thought it takes care of itself. Now im thinking, am i suppose to change the resolution in the Image Size dialog box from Photoshop?
Questions:
1) if I want to print using my canon i9900 printer, do i concern myself with the resolution? I think that most top notch consumer printers are best when resolution is between 225 - 250 pixels or something like that. How do you know? How do you tell what resolution your printer prints best at and do you indeed make these changes before printing?
2) if you dont use this "magic" resolution number then what happens? for instance, if i find out that i should be changing my resolution in photoshop to 250 before i print and i dont change anything - would it make a difference?
3) so what is good advice for home printing when using photoshop regarding the resolution in the Image Size dialog box?
troy
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—Korzybski
hmm. i actually understand what you said! I do appreciate the info.
the reason I asked this question was because I had read in Layers Magazine - http://www.layersmagazine.com/the-reality-of-resizing-changing-image-resolution-without-changing-quality.html and thought I had to "actually" change the resolution before printing. Something I never worried about before.
troy
There's an excellent article in last month's Photoshop User (June 2007, pg. 48) - The Fine Art of Printing.
In this article, Paul Caponigro does an excellent job of making sense of pixels vs resolution...I suggest you read it.
He mentions one thing I think is important...and I quote:
I've been resampling to 360 for my 1440x2880 and (maybe it's my imagination) I think it looks better!
- Gary.
http://www.ledet.com/margulis/PP7_Ch15_Resolution.pdf
Sincerely,
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
whoa...
thats a whole chapter - i expected my question would only maybe need a few words to answer...... so what say you regarding this matter?
troy
Troy, that was to let you know what a deep issue this is, if you did not! Not inkjet specific, more general and press/halftone related but still useful.
To lightly get into your specifics questions:
You know by testing and performing evaluations. Others may have done this for your make/model (it can be very specific) - but even then you may wish to do so for yourself. It is also very much dependent on the image content, image sharpness and other print variables in the printer driver or RIP etc.
Generally, it is accepted that one resizes to the desired output size with resampling turned off. One has the native pixel resolution with no interpolation. One may find that they have 476 ppi at the desired output size. They can then choose to send the extra pixels to the printer as is, or to resample this resolution down at this desired print size (in a duped file), apply some sharpening (if desired) and then output. What ppi target to resample to then?
Lineart or sharp text like elements in raster files generally need the maximum printer resolution, which is why vector formats are often preferred as they have no fixed resolution until rasterized. This provides the most detail and sharpness. But contone images often need a lot less resolution and excessive resolution may make things appear softer rather than sharper.
Halftone press reproduction uses a rule of thumb where at final repro size, the input ppi is x1.5 to x2 the size of the output halftone screen ruling. So at 5x10 inch size using a 150 lpi screen ruling the input size would be 5x10" @ 225 or 300 ppi. Stochastic dither (often in inkjets but sometimes on press) is more forgiving than halftoning, so one can get by with a lower quality factor depending on viewing distance and other variables.
As Epson printers often use some multiple of 360 dpi for printing (720, 1440, 2880) - Epson owners often report variable and sometimes slightly better results at 360 ppi over 300 ppi or some other arbitary figure. Many Epson users also use 240 ppi at final size as they find no difference over 360 for their images and viewing conditions (2/3 of the min. output dpi, although most print at higher res than min).
The wide format HP DesignJet at my work is a 600ppi native resolution inkjet, so 360ppi would not seem to be the choice for this make.
It is an important topic, but I would not loose too much sleep over this!
Sometimes yes, sometimes no. There are often no hard and fast rules in imaging, just rules of thumb (and there are always good reasons to "break" the rules too). It is both a science and art in my opinion.
Here is a good link on such printing:
http://www.normankoren.com/makingfineprints.html
http://www.normankoren.com/printer_calibration.html
Hope this helps,
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
Works perfect!
That being said, if I want to print right from my editing program...I just resample to 240 ppi...resharpen and print. I use a Canon i960.
hey Ric,
you see here is a good example of of what happens when i read or the proverbial "a little knowledge is a bad thing"......
Until the other day if I wanted to print, whether or not I used CS2 or whatever, id just print from the file menu and select Photo and the paper I was using from the dialog box that happened to come up when using a canon i9900. And for me thats all i knew, and i figured that was all to it.
BUT..........
Now I read that before you send an image to a printer you should have the resolution set to 300 dpi ( or some other number - some now say "360" ). Ive never in my life heard that / or done that. Thats where my confusion came in.
one example:
if i have an image that i took. I then crop the image to 4X6. i then go to photoshop and under image size i notice that the proportions are correct but maybe the resolution says 72 or 150 or whatever. I never would have cared nor known to care i would have just printed and selected photo quality. Now im thinking im suppose to change the resolution to 300 before i go to print.
Now I hear that you "resharpen" after that???
troy
thanx for a very comprehensive explanation!!! it does help my understanding... i appreciate the time you put into your reply!
in the long run, im not losing sleep over it. Just trying to understand a little more each day about how to make my images "print" a little better. Or at least to take advantage of the tools / software that im trying to use..
thanx again!
troy
Troy, when you crop is there a value in the third box in the toolbar - i.e.
[ 4" ] [ 6" ] [ 300 ] ?
If there is, Photoshop is resampling your imgae. If not it won't add or remove pixels.
my words, my "pro"pictures, my "fun" pictures, my videos.
Hi Steve,
i dont have access to Photoshop CS2 but i know what you mean, On the toolbar i leave where is says resolution blank. I then crop an image to constrained proportions such as 8X10. If i then go to image size, Ill see in the dialog box that i have an image that is indeed 8X10. The resolution in the box under these dimensions might say something like 235 or whatever. In the past whatever number was there didint matter to me! But now from what ive read, heard, "dreamed"..... im suppose to "up" or lower the number to 300 or 360, depending on who you ask, which will propably upsample the image slightly before I print. Thats my question - do I indeed "want" to do that?
i never asked before becasue im only NOW TRYING to USE CS2 exclusively for all my editing.
troy
my words, my "pro"pictures, my "fun" pictures, my videos.
thats what ive done until i started reading!!
damn reading!!! reading always gets me in trouble - thats why i deplore reading!
thanx Steve!!!
troy
I wondered if this topic would not get complicated quickly. There have been many discussions in books and on the web about how to set up image files to send to the printer - either linotype or RGB inkjet.
There are numreous experts who feel that images need to have 300 ppi for image smaller than 11x14 or so ( closer viewing distance ) and maybe 200 ppi for images 16x20 and larger, with the image scaled appropriately to size in Photoshop before being sent to the printer - bigger viewing distance for larger prints.
I have read discussions about whether 300 vs 360 ppi is better for an Epson inkjet printer ( printing at 1440 say) but have never tried it fof myslef.
So what I propose to do - is take an image that is 2880 pixels ( 8 inches x 360 ppi) by 3600 pixels ( 10 inches at 360 ppi) so that I have good detail and lots of original pixels to work with .
I will print this straight to my Epson 4000, I will also change it to 300 ppi without resampling ( eg: pitching some pixels) and let the printer scale the image to 8x10, and do the same thing at 72 ppi without reesampling and then see if I can see differences.
I have been thinking about how to demonstrate subtle differences in prints ( if they exist) on the web -- Maybe scanning the prints with a flat bed scanner and posting 100% crops from that might work.
As a practical matter, I tend to send my images to my Epson at 300 ppi - it is just simple and I tend to be lazy - and the prints look fine - I'll see if I can make them look better with 360 ppi. Who knows?
I know that Andy says not to worry about it for printing via smugmug - just send the entire full size file and let them worry about resizing if necessary. Sounds like a fine idea to me.
Moderator of the Technique Forum and Finishing School on Dgrin
Well, if you resized to the new final output size/proportion with resampling off, then this is the true amount of pixels in the file. If the figure was 72 or 150 ppi, then you know you have a less than ideal situation, but depending on image content and viewing distance the 150 ppi input may be acceptable.
If you had more than 300 ppi, then this may be in excess of what is needed.
Resampling up, inventing pixels from 72 or 150 ppi to 300 before printing may lead to no better or perhaps worse results than simply sending the lesser amount of pixels to the printer (depending on many variables).
Perhaps, perhaps not! I guess you mean with resample on now.
If resampling up, see the paragraph above.
If resampling down, then...
Resampling down softens the image a bit, so thus either using Bicubic (regular) which has a small sharpen built into it, or Bicubic Sharper which has a stronger sharpen in it - or by using USM or Smart Sharpen after the resample (which could be done using the Bicubic Smoother command so as not to introduce sharpening artifacts before USM etc).
I told you that resolution and printing was a deep subject!
Make the subject as simple or complex as you like. Perhaps only worry about all this if you find a print that you are not happy with, if the majority of printing in your chosen workflow that 'hides' all this stuff works in the majority of cases.
Regards,
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
Pathfinder, as you likely know - if you did try, you may not see any difference, depending on image content and perhaps other variables! I think it would be most evident on fine sharp diagonal lines or curves, as opposed to 90 degree angle fine detail. Fine regular repeating patterns/detail would also be a good thing to evaluate. From memory the differences reported are only minimal - often these demanding inkjet printer jockeys are fine art photographers selling expensive prints or printing for competition, exhibition/gallery display.
I have been involved in a few of these discussions before, what I took away from them regarding the setup of a good test is as follows:
1. Use vector artwork in addition to photography, rasterize the vector art into Photoshop at the same output size but differing resolution, say 100-150-200-240-300-360 ppi or whatever. This way one is not skewing the evaluation by resampling a large original down. Have a copy of the vector art printed direct from Illustrator or from Acrobat PDF to the printer at this size, to compare against the Photoshop RIPed files.
2. Similar to point 1, scan an original on a flatbed at the same size but differing resolutions.
3. As you suggest, using a good digicam shot that has many pixels, print the original pixel content and then try resampling down to different resolutions in dupes at the same target print size.
This third option is the most subjective of them all, due to resampling methods and or sharpening skewing the evaluation. I think all three elements are needed in the test suite of images.
Creating such a printer test form is on my ever expanding "to do list".
Sincerely,
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
I got busy last night ( watched a movie on TV for goodness sake's ) and I'm gratefull to have your suggestions as a result.
My suspicion is that for most images we will not be able to see a discernable difference with good photographic images. And yes, this topic seems to pop up most in Fine Art Photographers printing exhibition grade prints.
Perhaps, as you suggest, things will be more visible with vector based images - but I do not create vector based images as a photographer - Maybe if I began to create borders and titles, kind of liked Ginger used to do so nicely, I might see more of a difference. I'll keep that in mind. I was really thinking about using one of the color calibrations test printing images - like the one from Smugmug or Bill Atkinson.
I justy thought I'd try a couple frames from a 1DsMkll that were sharp, exposed properly and sharpened nicely for printing. My interest is not whether I can create a situation where a change is visible, but rather, is this something I need to seriously need to consider when printing > 13x19 or so.
I have an Epson V-7000 flat bed, so I could scan an image - but a printed image will have been de-screened and resharpened in the scanner software, so ..............
Moderator of the Technique Forum and Finishing School on Dgrin
1: Vector art can be "photo realistic" and use gradations, blends etc. It is not always text, lines and filled geometric shapes. Some good free ones can be found on the Adobe Exchange website and often vector apps have some samples.
2. With digicams being so common today, we may not have easy access to film or reflective prints or even a scanner anymore. I propose using a Fuji Frontier contone photo output of some holiday snap crops, so no dot issues to worry about.
Both of these methods are moving away from your interest. Yours is workflow specific, while mine is trying to establish the base response of the printer in ideal conditions that may not be apparent in a given workflow. Don't worry too much about my suggestions, they were more "for the record" than anything.
Sincerely,
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
I decided to use a frame shot in Colorado during the workshop with Marc's Crew, since I know it was shot on a tripod, and I can use the entire frame which will give the number of total pixels needed.
I opened the file in ARC 4.1 and processed as I typically do - (the exposure was accurate) - just needed a little Recovery of a few dots of Highlight slider
I then opened the image into Photoshop CS3 in the ProPhoto color space as an 8 bit image. I found a likely black and white point, and adjusted with Levels to fine tune the color balance. I moved to LAB and sharpened the L channel with values of 30,30,2 - no extremes here, just a bump to make the image look a little sharper ( we could digress and argue abut what parameters would be best - but that is not the topic in this thread ) The image was brought into Photoshop from the RAW convertor at 300ppi. SO I did Image > Size to verify this and captured the dialogue box and dropped it into my image in the sky where you can see it. Shifted to sRGB. Here is my test image....
The full file is 9.707 by 14.56 at 300ppi
I then printed the central 8x10 portion of this image on Premium lustre paper using the correct profile for my Epson 4000 at 300ppi and with no color management by the printer.
I then reduced the size of the image slightly by increasing the ppi to 360 ppi with resampling to keep the image size the same. I then printed the central portion of this image just like the first one, at exactly the same size. I incorporated the Image dialogue box as before so it is clear the ppi of this image.
I then went back to the history palette before changing size of the image, and converted it to 72 ppi without resampling. The image size promptly increased to 72.806 x 48.542. I then printed the central protion of this image as before. I used the Photoshop printer dialogue box to diminish the size to the same as the first image 9.707 by 14.56.
The upshot of this is that I now possess three 8 x 10 prints that I cannot distinguish from one an other with an 8x loupe.
Maybe the fine art printers are that much more observant than I am, but I cannot discern any difference between the images. If there is interest, I will try to scan the prints and upload them for other's perusal - but maybe tomorrow.
Moderator of the Technique Forum and Finishing School on Dgrin
So then if i take all the info gathered here and incorporate it into what I already know ( hoping its correct ) i can answer my original question this way.......
When sending out images to online print services and such its a good idea to have the resolution set to 300 dpi. Ive heard that sometimes when sent through some internet services jpeg files get converted to 72 dpi and the guy / machine at the other end might reset the resolution which then might not print properly. This issue however does not apply to printing from smugmug.
Given that Im using a Canon 30D, when printing a 8X10 ( the biggest print size id ever print ) there will be enough information so that very little resizing or upsampling should be necessary. Therefore I need not worry about changing the resolution to 300 before i print on my "home printer".The differences ( if any ) might be inperceivable - especially to my poor eyes. If my image contains lots of sharp details / lines sharp text etc. a lower resolution might even be favored. Unless however if the resolution is obviously low - it would behoove me to "upsample" the image. I then could print out at both resolutions to see if there is a difference. And it is here that the question might be best answered in that - I should "print" out my image to "see" if there are any differences rather than rely on a standard number ppi.
I think this answers my question....
Thanx to all who contributed to my understanding.
troy
For me, if you shoot RAW, the secret is to bring the image into Photoshop at 300ppi or so then - you should not need anymore pixels at that point for modest images like 8x10.
Moderator of the Technique Forum and Finishing School on Dgrin
Good point Pathfinder and obviously not only restricted to camera raw files - if all images are resized with resampling turned off to the desired minimum or optimum resolution, then one knows that the image is at the preferred largest output size and that if it is used at a larger print size then quality may drop.
Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
I don't think this is quite right and many users are confused by this. When you print at an online photo service, the ONLY two size parameters that matter are how many pixels you give them and the size print that you request from them.
The size a given image is labeled at (like 8x10 or 12x16) is just a label on the image (e.g. a piece of meta data). It has absolutely nothing to do with the pixels and nothing to do with how Costco prints it. Costco doesn't even look at it.
The labeled ppi is also a just a label and it is calculated by taking the real number of pixels and dividing by the labeled size. Costco doesn't look at this value either.
So, if you have a 2000x3000 pixel image and you asked Costco to print an 8x12 image from it, you would get exactly the same print if your image was labeled as an 8x12 at 250ppi or 16x24 at 125ppi or a 4x6 at 500ppi. Costco ignores the labeled size and ppi because you gave it a fixed number of pixels and you told it the size you wanted to print. That's all they need.
Now, one thing you do have to watch out for with Costco is their plug-in that does the uploading might actually downsample the image to a smaller number of pixels before uploading. This is an actual resample that would change your 2000x3000 pixel image to 1000x1500 or something like that. By default it does that and it also uploads faster because it's a smaller size. You have to find the right checkbox in their uploader to tell it NOT to do that. But, again, this has nothing to do with the labeled image dimensions or the labeled ppi.
To repeat, the only two size parameters that matter when you tell Costco to print a specific size are the number of pixels you start with and the size you tell them to print.
Costco's printer will have a "native" resolution that it wants to print at. This will vary by printer and since they use different printers for different sizes, this will vary by print size you order too. For moderate sized prints or enlargements, it it safe to say that the printer will probably have a "native "resolution somewhere in the range of 200-300 pixels per inch. If it was 250ppi, then for an 8x10, it would need 2000x2500 pixels to feed the print head. If you don't give it exactly this number of pixels, the software that drives their printer will take the number of pixels you did give it and resample them to match what the printer needs. This is all done automatically by the printer software and for moderate amounts of resampling is very high quality.
I generally do NOT resample my images (e.g. change the number of pixels) to try to match the printer's native resolution exactly. This is because I believe the printer's software does a fine job doing the resample and it's often hard to find out exactly what the native resolution really is. If you resample to try to match it and you don't get it perfect, then the printer software will resample again. You want to avoid multiple resamples since each one is a bit of an image degradation.
The ONLY time I think about resampling myself is if my image is more than 2x off from the printer's native resolution. So, if I had done some major cropping of an image and only had 800x1000 pixels for an 8x10, then I only have 100ppi at that size. In that case, I'd manually resample myself (and resharpen afterwards) to make the number of pixels match what the printer natively wants. I'm doing the resample myself in this case only because it's such a big resample that I'd like to control the sharpening that happens afterwards rather than leave that to an automatic process. If the resampling is a much smaller percentage I think it's better to make sure there aren't two resamples and just let the printer software do it once.
Is this clear as mud now?
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BTW - i didnt mean to use costco or any other printing service by name. But I have been told that sometimes this happens.....
from my discussion with an expert
"My suggestion to do it, is only if you're printing from some place where 300dpi is the default setting on their machines and an image you send them at 233dpi might get manipulated to fit their specs. On occasion I've seen this happen."
but that for the clarification and I will replace the name mentioned...
troy
You don't need a whole chatper, that's for sure. KISS.
This is old but gets to point quickly and easily:
http://www.digitaldog.net/files/Resolution.pdf
Author "Color Management for Photographers"
http://www.digitaldog.net/
I did mean to name Costco by name because I've printed there and found that their onlne uploader does downsample the resolution of the image by default. You do have to find the checkbox that tells it not to do that. I've gotten some really good prints there, but their defaults are geared more towards 4x6 prints rather than enlargements.
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