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Archive 2013 · Image PPI to Printer DPI
  
 
blitzn
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p.1 #1 · p.1 #1 · Image PPI to Printer DPI


Hey all,

I've been reading about printing, specifically how I need to prepare my images to get the best quality print. (I own a 5Diii and Pixma Pro 9000 mkII - both new so I'm a newbie to printing). All the online stuff I find seems conflicting in its advice (240 ppi vs 300 vs 360 vs "native to the printer" etc - sRGB vs Abobe RGB)... I' looking for a good read on this so I can bring my own technical knowledge into my printer setup and image processing. So the question is:

What book/article would you recommend so I can get educated on printing and image prep for printing.


Thank you in advance for your suggestions!

Tom



Jan 25, 2013 at 07:23 PM
hugowolf
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p.1 #2 · p.1 #2 · Image PPI to Printer DPI


I can recomend 'From Camera to Print and Screen'
http://www.luminous-landscape.com/videos/tutorials/camera_to_print_and_screen.shtml

If you want it in book form:
http://www.amazon.com/Digital-Print-Preparing-Lightroom-Photoshop/dp/0321908457/ref=sr_1_1?s=books&ie=UTF8&qid=1359144549&sr=1-1&keywords=Digital+print
but the book isn't due out till spring.

Epson printers, 360 or 720 ppi is optimal. For HP or Canon, 300 or 600 ppi. The oft quoted 300 ppi is based on 150 lines per inch (lpi) for offset printing, although many C-type prints are made on Fuji Frontier machines with 300 ppi, or Noritsu machines at 300, 320, or 400 ppi.

The 240 ppi is often seen as the limiting resolution for a high quality print.

Brian A



Jan 25, 2013 at 08:17 PM
cgardner
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p.1 #3 · p.1 #3 · Image PPI to Printer DPI


DPI is a historical printing standard / term of art and the 300ppi requirement for reproduction dates from the introduction of B&W laser printers. My career spanned analog screens > digital equipment and here's the historical background as I understand from using it, researching it, buying it, and managing it for a living.

DPI = dots per inch comes from letterpress and offset printing which original used "hard" dots space 85, 120, 133, 150, etc per inch to create intermediate gray tones on white paper with black ink. The screen ruling would be selected based on what the paper could handle without the 90% shadow dots filling together. 85DPI was pretty standard for letterpress newsprint, 133DPI or 150DPI screening on clay coated papers which don't absorb the ink like a blotter. I created halftones and color separations with screen like that in the 1970s at National Geographic where I worked as a lab tech.

I first saw PPI mentioned in the context of printing vs. DPI in the mid 80s with the introduction laser printers. Like a printing press gray tones on a B&W laser printer are created with regularly spaced dots of various sizes. But on a laser printer they are created with sub-dot patterns within each printing dot.

Each printing dot was actually and 8 x 8 grid which was exposed one 8 row at a time as the paper passed over the fixed print head. The process would repeat 8 times to complete on row of printing dots. If no parts of the grid were exposed the tone of the dot would be white (just paper). If all 64 of the grid cell were exposed by the laser to fuse the toner the dot would be black. If half the grid cells were exposed the tone for that dot would be gray. By varying the number of 0-64 sub cells of each PRINTING dot which were solid the overall image had 65 discrete tones of gray in it.

As I understand it from reading trade journals at the time the 300 pixel per inch standard was arrived at by testing. It was well established from years of offset printing how fine a line ruling was needed at reading distance for the eyes not to resolve the dots: 150 DPI or 150 discrete dots to the inch for B&W and 133 DPI for color. It was possible to use a courser screen ruling for color because the four colors overlapped at different angles to create more continuous coverage of the papers.

Different digital image (PPI) to 150 DPI sampling rates were tried and shown to people to rate which sucked and which fooled them. The consensus was that between a 1.7 to 2 pixel > printing dot ratio produced the best looking results ON A B&W LASER PRINTER. So to get a realistic image on the 150 DPI laser printer a pixel resolution of between 255 ppi (150DPI x 1.7) and 300 ppi (150 x 2) was needed.

Where it gets really confusing is how the 2 for 1 downsampling from 300 pixels per inch get translated (on a laser printer) into 64 block grids spaced 1/150th per inch center to center. That's done mathematically at a level beyond what I understand.

Like many conventions submitting 300ppi resolution images was used by people like magazine art directors who really didn't understand technically why it was a convention. But as with the laser printer development test it was obvious that files with lower resolutions sucked.

Back in the 80s - 2000s I was production manger and later director of a publication printing plant printing. Well into the 2000s we did most of our reproduction for magazines by scanning transparencies. The few digital images we used were reproduced in smaller sizes. If you took the pixel dimensions of the SOOC file and divided by 300 it told you the max. size it would print acceptably. A 2.1 MP camera producing a 1200x1800 file SOOC could make a decent looking 4 x 6 image. Push it any larger by resampling in Photoshop and the image quality deteriorated.

For a full page 8.25 x 10.75 magazine page you needed a camera that produced (8.25 x 300) x (10.75 x 300) = 2475 x 3,225 = 7.9 MP SOOC. For a two-page 16.5 x 10.75 = 4,950 x 3,225 = 15.9 MP SOOC. The 8MP sensors didn't arrive until around 2004. 16MP sensors several years later. Now the SOOC resolution of some cameras is so large is is necessary to downsize their SOOC files for use on a two-page magazine layout.

The 300ppi min for reproduction is still used as commercial standard because most commercial / editorial work stills winds up in print in a magazine at some point. But advances in post processing and inkjet printing has made it obsolete for images not printed on a high speed magazine press.

Inkjet work differently

Ink jets have discretely spaced jets on the print head (Typically 300 / 360/ 400 per inch) but the jets don't form discretely spaced dot on the paper as with offset printing. The paper and the print head can move in increments smaller than the jet spacing. For example by moving the paper 1/2 the speed as normal a 300 jet print head will put 600 "splats" of ink on the same area of paper as at normal speed. The printer can control the the movement of the head across the paper the same way, and control the frequency and volume of the ink spurts. All those physical design factors translate into needing fewer ppi to get acceptable results vs. printing on an offset press.

The best way to find out the best ppi for a printer you own or print on at a vendor is to take a section of a file, resample it in Photoshop so it is the same size image but changes in PPI resolution, print them and compare. Compare them side-by-side and like the laser printer testers 30 years ago you'll know by eye which suck and which are acceptable.

The min ppi which looks acceptable will vary with printer / paper choice and other variables, and with content. If an image doesn't have fine detail, like skin in a portrait, a lower ppi level will be acceptable. If the image has fine detail it will need more ppi to look good. But more ppi isn't always better. As with lens resolution as you stop down at some point, you need to determine with testing on your equipment, the test image IQ will start to deteriorate as ppi increases. Fine detail will get lost in the sea of overlapping ink spatters.

Personally I used a Apple Quick Take 100 .8MP camera in late 1994. Even at postage stamp size the IQ sucked.

In late 2000 I bought a 2.1 MP Kodak DC290. On a desktop inkjet I could get a 4 x 6 print that was an acceptable match to a 4 x 6 film neg photo print. Printing on more forgiving $25,000 dye sub proofer I was able to get acceptable looking 12 x 18 prints, some which are still on my wall. Experimenting with Genuine Fractals and a wide format ink jet I was able to create an acceptable 24 x 30 print for a portrait IF you looked at it on the wall from across the room.

I waited until 2004 and the 8MP Canon 20D before jumping to DSLR and giving up film completely so I would be able to produce 8 x 10 prints that looked as good as an 8 x 10 created on film. I upgraded to a 14MP 50D and can get the same quality in a 12 x 18 with a SOOC file and print larger as needed by applying PhotoChops. I don't feel any compelling need to buy a higher resolution body because I have not made a print larger than 12 x 18. When I make a 600 x 900 file for a web page I'm actually "throwing away" more pixels vs the SOOC file than I did with the 2.1 Kodak and must apply things like USM to compensate.

YMMV - If I was making a living selling large fine arts prints of landscapes or posters for commercial clients I'd buy the biggest MF sensor I could afford because I would have a compelling need for more pixels.




Edited on Jan 26, 2013 at 11:39 AM · View previous versions



Jan 25, 2013 at 10:27 PM
blitzn
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p.1 #4 · p.1 #4 · Image PPI to Printer DPI


Wow- thank you both for the thoughtful and extensive information. I knew that to print I would need to embrace a long learning process, and these posts prove it!

Thank you so much..... and now I'm off on the journey.......



Jan 25, 2013 at 11:51 PM
Bifurcator
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p.1 #5 · p.1 #5 · Image PPI to Printer DPI


Well, my opinion might seem a little harsh but:

Unless your intention is to become a fussbudget and spend long hours with a magnifying glass in your hand comparing pixels there really is nothing to learn. I spent weeks examining every aspect of printing in the modern studio and I managed a page-layout company for a couple of years in the mid 90's. As C. Gardner mentions inkjet is not like laser printing! So you can ignore anything about laser printing.

You can pretty much toss all of this learning curve into the trash can and save yourself a heap of mental strain!

Get it looking good on screen, press print, auto-scale to page and check the Let Printer Manage Color box. The one time in fifty it doesn't look as expected hold up the print next to the monitor, decide what needs changing in the print, do that, and reprint.

For A4 printing about 150PPI on up is fine and for your B3 sizes 120PPI on up is fine. And you can't tell the difference between 200PPI, 217PPI, and 600PPI. With your camera that means you don't have to worry about anything (unless you're cropping down around 100% or something... ), just print it.

If you haven't tried it already I urge you to do so before going on with this (IMO) wild goose chase. Get an image you like, process it. If it's something that needs to look "sharp" sharpen it a little more than you would for forum posting, and print it at the full camera resolution (no scaling) on an A4 sheet of photo-grade paper - this will probably be around 700PPI with your camera. Then scale it to150PPI, re-add any sharpening that was lost and print it again at A4 (about 8x10). Now leave the room and have someone tac the images on the wall. Reenter the room and see if you can tell any difference.

If for some reason you have superman's eyes and can actually tell a difference then print another at 180PPI in the same way and try that.

Why is this true? Because a printer doesn't actually have a "native resolution" - that's a myth! Every image you send to your printer will be MASSIVELY dithered! All! No matter what PPI you send. Try it. Find some person on-line who thinks he knows what your printer's "native resolution" is and then make a pattern with 1 pixel wide dots or lines and send it to your printer at that PPI. Now look at it at between 3x and 10x magnification. This is what you will see:



Printer output examined. Data was sent at the printer's "native resolution"
See below to understand the pattern data.
You're seeing six black pixels and four white pixels of the pattern.



Here's what the full pattern looks like when zoomed up in photoshop (source data, screen grab).



Here's the full source image with the embedded pattern (top/left of stem)


It pretty much doesn't matter what PPI I send this data to the printer at. Anything over about 150PPI will look just like this. If the PPI is too low however the printer's conversion engine will add too much smoothing (interpolation) which can indeed make image detail appear soft - but that's typically not until lower than about 120PPI.

Consider also viewing distance! This image is from a D700 and looks totally awesome wall sized! How can this be? Because no one sane anyway looks at it from less than 1 meter away and probably not less than 4m.



See the green box below for a close-up of the print above - also in green. Focus distance about 5m with 35mm Equiv FL.




Taken from about 1.5m away with an 85mm Equiv FL. (See the green box in the full image above)



The rule I've found is that if it looks good on A4 (8x10) then you can use the same data to print any size - all the way up to the size of the Empire State building, the state of Texas, or the size of any planet you choose. Only you need to consider the cost of ink.


So the conclusion is as stated in the beginning. Just print and don't worry about it. Add a little extra sharpening over what you would for forum posts, let the printer manage colors, and enjoy - without becoming a fussbudget. If you have your color profiles set and your monitor even close to being calibrated, you need not chase the wild goose any farther than that.


Edited on Jan 28, 2013 at 07:12 PM · View previous versions



Jan 27, 2013 at 06:34 PM
blitzn
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p.1 #6 · p.1 #6 · Image PPI to Printer DPI


Bifurcator - with two kids in college, what seems like two fulltime jobs, and a lovely wife with whom I wish I could spend more time, your advise is welcome news. "Click on print" will be my first step as I think you may be right, I just may be happy with the results and I can go back to work, or walking with my wife - while we just enjoy the new wall art!

Thank you all for the input.



Jan 28, 2013 at 04:47 AM
marko1953
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p.1 #7 · p.1 #7 · Image PPI to Printer DPI


Wow, that's what i like about these forums, one reply gives a detailed, historical account of the history of printing, another says:
"Get it looking good on screen, press print, auto-scale to page and check the Let Printer Manage Color box."

I usually follow the KISS method "Keep It Simple Stupid" !




Jan 28, 2013 at 11:11 AM
RustyBug
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p.1 #8 · p.1 #8 · Image PPI to Printer DPI


+1 @ practical limits for routine ... vs. ... exacting criteria for "fussbudget".

This is my "fussbudget" book.
http://www.amazon.com/Fine-Art-Printing-Photographers-Exhibition/dp/1933952318

Yet my last printing was @ my local Staples (nearest lab is 70 miles away) and I received awards in (regional) competition (i.e. not hindered by the printing). Granted this printing was only 12x18 (trimmed to 12x16, matted into 16x20 frame), but the image "held up" in competition without using the "fussbudget" approach (despite my typical "fussbudget" tendencies).

My typical "fussbudget" advice is in line with Uwe Steinmueller's advice at matching dpi and "native to the printer" rastering ... which typically means, call your printer and let him guide you to what dpi you should be preparing your file to be printed at. But since you're doing your own, and it is only going to be at nominal print size ... just go with the OEM recommendations and you should do fine to start.

There is a time & place for "fussbudget" ... and in those instances where it is needed, it is valid for consideration. But for getting started ... hit "Print" and go from there. "Fussbudget" can wait (for now) while you enjoy the "KISS" approach ... even though it may prompt a future desire for a "fussbudget" approach someday.

Despite my "fussbudget" tendencies to align dpi/rastering/file size/print size/etc. ... they all play "second fiddle" compared to aligning my comp/crop for intended print size ... i.e. it gets printed at whatever fits.

Here's the one I took to Staples (hard to believe the "fussbudget" me actually did that) for a competition.







Jan 28, 2013 at 01:38 PM
RDKirk
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p.1 #9 · p.1 #9 · Image PPI to Printer DPI


I waited until 2004 and the 8MP Canon 20D before jumping to DSLR and giving up film completely so I would be able to produce 8 x 10 prints that looked as good as an 8 x 10 created on film. I upgraded to a 14MP 50D and can get the same quality in a 12 x 18 with a SOOC file and print larger as needed by applying PhotoChops. I don't feel any compelling need to buy a higher resolution body because I have not made a print larger than 12 x 18. When I make a 600 x 900...Show more

I'm more of a fussbudget than you, Chuck. Because I routinely make 20x30 and larger prints, I waited until the 5D2 to retire my medium format film cameras.



Jan 28, 2013 at 03:43 PM
cgardner
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p.1 #10 · p.1 #10 · Image PPI to Printer DPI


Mine was a historical overview of why 300 ppi became a "knee-jerk" benchmark for output resolution. It reflects my learning curve of starting making halftones with screens and litho film. Like any history you should learn from it and move on to avoid making mistakes you might have otherwise out of ignorance and bad advice, such as needing 300 ppi output resolution.

300ppi is still a valid criteria for images printed in magazines but not for ink jets. I said that and suggested taking an image and printing it at various output resolution on your printer to determine what is the lowest resolution that YOU find acceptable. That will vary by individual, content of the photo, and viewing distance so there is never one "right" answer that applies to all photos at all viewing distances.

Billboards can look "normal" despite having dots the size of golf balls if you view them from far enough away that the eyes can't resolve the dots. That's what makes the results acceptable or not. You can make the eyes see an image as continuous by making the dots smaller, or making the pattern more random. Ink jet do both compared to offset which is why much lower output resolution looks acceptable.

In terms of perception of 3D shape and texture in a photo, beyond reading distance the eyes react less to texture clues and more to the overall contrast seen on planes of the objects to discern their shape. A photo of a sailboat on the ocean will stand up better to enlargement on a billboard than a close up of leaves. Your brain will be able to identify "Hey that's a boat" from the outline clues created via contrast. But from a distance the shot of the leaves will just look like a green blob.

Because of that RustyBug's train tracks photo with strong contrast would stand up well to extreme enlargement. Bifurcator's shot of the sand dune? It will look like a tan blob.

But variables like content only become a factor when you start making large prints which will be viewed from a distance. Then you also have the problem of the overall impression from across the room, and how the image looks from reading distance when the viewer walks closer.

John Singer Sargent was a painter who created larger than life portraits. Seen from across the room entering the gallery they seem to have fine detail. But on close inspection you see the literally troweled on the paint with a mixing knife. What created the illusion of detail was how he placed white specular highlights in all the "right" places to create the impression of "hard" lighting (in photographic parlance). It tricks the brain into equating contrast in the 2D rendering with more angular 3D shape.

When USM is applied to a photo it creates a similar illusion the same way by increasing the contrast at tonal boundaries. So as you enlarge an image and the fine detail and edges turn to mush you can compensate by applying more USM. It will look worse at pixel-peeping reading distance but make the seen-from-a-distance view seem more similar to a smaller print seen closer.

The more important lessons I learned in a career in reproduction weren't the technical ones but the perceptual ways that the brain is fooled into thinking a 2D pattern of contrast is a 3D object. Those lessons help me to understand how to apply the technology to get the desired perceptual result for a given subject, print size and viewing distance.







Jan 28, 2013 at 04:04 PM
 

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hugowolf
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p.1 #11 · p.1 #11 · Image PPI to Printer DPI


Is it so much work, so time consuming, and worrying in Lightroom to select a profile from a drop down and type in 360 before pressing the print button? QImage even selects the printer's native resolution for you.

Brian A



Jan 28, 2013 at 04:21 PM
redcrown
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p.1 #12 · p.1 #12 · Image PPI to Printer DPI


For the "fussbudgets", an old bookmark of mine:

http://www.rags-int-inc.com/PhotoTechStuff/Epson2200/



Jan 28, 2013 at 04:40 PM
cgardner
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p.1 #13 · p.1 #13 · Image PPI to Printer DPI


hugowolf wrote:
Is it so much work, so time consuming, and worrying in Lightroom to select a profile from a drop down and type in 360 before pressing the print button? QImage even selects the printer's native resolution for you.

Brian A


The question here wasn't so much how to do it but rather why it is better to do it one way or the other. You and I understand what native printer resolution is and it's implications regarding output but does the OP?

Vince Lombardi famously started a coaching session with "Gentlemen, this is a football". It wasn't that the players didn't know how to play the game, they just had different concepts of what the correct way to play it was. Stepping back and starting over from the beginning gets everyone to understand and work towards the same goal. With printing, however you do it, the goal is to fool the brain into thinking the image is continuous tone when the method used to created it isn't.

The problem with the internet is you don't know what incorrect assumptions might underly a seemingly basic question. Just the use of the term DPI is a red flag because it does not apply to ink jet. Native resolution (print head spacing) doesn't equal DPI because the print head and paper can move in less than native resolution increments to overlap the jets of ink. But just telling the OP "Erase the term DPI from your vocabulary because it doesn't apply" doesn't help him understand why.






Jan 28, 2013 at 04:44 PM
dmacmillan
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p.1 #14 · p.1 #14 · Image PPI to Printer DPI


blitzn wrote:
Bifurcator - with two kids in college, what seems like two fulltime jobs, and a lovely wife with whom I wish I could spend more time, your advise is welcome news. "Click on print" will be my first step as I think you may be right, I just may be happy with the results and I can go back to work, or walking with my wife - while we just enjoy the new wall art!

Thank you all for the input.

Good to hear you have your priorities in order. I have a 5D and a Pixma Pro 9500 II. My monitor is calibrated, so I click the print button and 98% of the time a get a spot on print.

Just try it. If your results are close to what you see on the screen and you're satisfied, you're good to go.

What software do you use? I'm printing from either PS6 or Lightroom 4.1. I normally just let either program handle all the details. Every once in a while I'll use NIK Sharpener Pro to do the sharpening for printing. It does a slightly better job under some circumstances.

BTW, using the above easy technique, I recently printed some 13x19 prints from 35mm and 4x5 negatives scanned on a new to me Epson V700. I am very familiar with the negs and have made wet lab prints from them using a Beseler 4x5 enlarger and a Leitz (Leica) Focomat enlarger. My results were as good or better than wet lab prints, I had far more flexibility in dodging and burning with this workflow.



Jan 28, 2013 at 05:02 PM
RDKirk
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p.1 #15 · p.1 #15 · Image PPI to Printer DPI


The problem with the internet is you don't know what incorrect assumptions might underly a seemingly basic question. Just the use of the term DPI is a red flag because it does not apply to ink jet. Native resolution (print head spacing) doesn't equal DPI because the print head and paper can move in less than native resolution increments to overlap the jets of ink. But just telling the OP "Erase the term DPI from your vocabulary because it doesn't apply" doesn't help him understand why.

And of course, printer manufacturers boldly display their dpi in their ads and packaging, so how can everyone else say "dpi doesn't matter" without explaining why it does not matter?

Thanks for the thorough explanation of how we got to where we are, Chuck.



Jan 28, 2013 at 05:36 PM
Bifurcator
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p.1 #16 · p.1 #16 · Image PPI to Printer DPI


blitzn wrote:
Bifurcator - with two kids in college, what seems like two fulltime jobs, and a lovely wife with whom I wish I could spend more time, your advise is welcome news. "Click on print" will be my first step as I think you may be right, I just may be happy with the results and I can go back to work, or walking with my wife - while we just enjoy the new wall art!

Thank you all for the input.

dmacmillan wrote:
Good to hear you have your priorities in order. I have a 5D and a Pixma Pro 9500 II. My monitor is calibrated, so I click the print button and 98% of the time a get a spot on print.

Just try it. If your results are close to what you see on the screen and you're satisfied, you're good to go.


Yup!

And just for the record I'm not saying fussbudgetry isn't fun and educational! Heck in those 2% of times when there is a problem the hundreds of hours you spent may even pay off - for you will know why the problem is happening and maybe even the best way to solve it. For me it was fun. I never used the information I learned for printing - ever. But I did get to answer a few hundred forum questions about how printers work, what happens to the image data throughout the pipeline, what profiles are about, the properties of various inks and papers, and etc.

And I might add that for other kinds of printing besides photographs on an inkjet a lot of it is actually required knowledge.


--
BTW: For magazines and such no one uses DPI or PPI. They speak in terms of LPI.
Oh, and that's not a sand dune... That's an enlarged section near her crotch. Follow the green boxes.



Edited on Jan 28, 2013 at 07:40 PM · View previous versions



Jan 28, 2013 at 06:52 PM
cgardner
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p.1 #17 · p.1 #17 · Image PPI to Printer DPI


The genius of profile based management of digital color is that is automatic. Like driving a car it's not really necessary to understand what makes makes the wheels turn until it stops working as expected. Then it's helpful to know your way around under the hood.

I start process control of color at capture with custom WB. That makes it nominal out of camera so regardless of what my adaptive eyes tell me based on the monitor image. I don't screw with it and don't mess it up. Because I don't mess it up with poor decisions when editing when I print using printer brand paper letting the printer manage the colors what the printer produces looks good too... automatically. I appreciate the genius in being able to do that automatically because I understand how it works.

The question of "do I have enough ppi" question got answered with the practical test I suggested 8 years ago when I bought an 8 MP camera. Now that I have a 14 MP camera I have more than enough ppi to make the largest print my printer can produce.



Jan 28, 2013 at 07:13 PM
blitzn
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p.1 #18 · p.1 #18 · Image PPI to Printer DPI


Cgardner said: You and I understand what native printer resolution is and it's implications regarding output but does the OP?

No I didn't and your post was so helpful for me - in part because I was reading a lot of conflicting information on the internet. I am a techie, well enough of one to understand everything you offered. So thank you, and also thank you to the others who have me feeling comfortable that the kiss method will be a sufficient starting point. My tendencies will be to become more of a fussbudget as I get deeper into the learning curve.

Thank you all.... T-



Jan 28, 2013 at 08:05 PM
dmacmillan
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p.1 #19 · p.1 #19 · Image PPI to Printer DPI


Kent (Rustybug) posted a link to "Fine Art Printing for Photographers:"

Here is a quote from a review of the book:
"Many photographers seem to have optimism that they can improve their pictures by more work and study. How else can one explain the many photography books on the market? Apparently some believe that they can improve the printing of the pictures that they've already processed in photo-editing software. Here's a secret. In most cases, if a photographer follows the instructions that come with his or her printer, the printer will produce as good a picture as possible." I regard this as wise words.

Modern inkjets are far more advanced than earlier models and your Canon is a very nice printer. A lot of what I read on the internet is years old and actually outdated. I like to know how things, work, but I am also a results oriented pragmatist. If I invest hours of reading and study, will all of this effort help provide better printing results? What options do I have for the time invested? How about actually practicing photography? How about taking walks with my wife or spending time with my grandchildren?

I had grand plans when I got my 9500 to do all sorts of testing and tweaking. I investigated some different papers and decided on a few that I thought met my needs. My results have been so good that I don't feel any need spending hours tinkering or reading technical tomes.

Edited on Jan 28, 2013 at 08:59 PM · View previous versions



Jan 28, 2013 at 08:58 PM
cgardner
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p.1 #20 · p.1 #20 · Image PPI to Printer DPI


LPI and DPI actually refer to the same thing, the spacing between centers of the dots. They actually are dots on the sheet so DPI is the more accurate term used by technicians who actually made the halftones and separations with hard dots, but we referred to them a "133 line screens" with the fact they were lines of dots taken for granted. Been there, done, that. Also taught it at a college for five years.

The original glass halftone screens (which we still had on the process cameras at National Geographic) were constructed by taking to sheets of glass with lines scribed in one direction 1/133th inch apart (LPI), filling them with pigment, then sandwiching them 90 degrees to each other to form the screen pattern (DPI). That was necessary because the technology didn't exist at the time to etch that fine a cross hatch on glass.

The halftone screen pattern with dot 1/133th in. center-to-center (133 DPI / LPI ) was created on high contrast litho film by creating a small (thousands of an inch) gap between the glass screen and film held on the camera back with vacuum so it created an umbra/penumbra gradient. That's how variable exposure was able to create variable size printing dots when the litho film was developed. It was something that required a great deal of precision and craftsmanship.

The contact screens we used to make halftones where a continuous tone pattern of 133 DPI dots on a sheet placed directly in contact over the litho film on the camera back. The gradients on the screen created the variable size dots on the litho film similar to how focusing the glass screen did it without the need to precisely focus the glass screen shadow pattern. We also had line screens to make line reproductions vs. dots.

My all time favorite quote on the subject was from a customer doing a color OK of a knife catalog in the mid-70s for the Guttman company (great name for a knife seller, no?). There was a problem with the cover reproduction on press and the CSR (not me) was trying to explain it to the owner who was there approving the press run using 10x loupe to examine the press sheet. Mr. Guttman interrupted and said, with a "Dots Smots, I sell knives and I pay you people to make them look good, so go do it..."

That's really all that matters: that the results coming off the end of the printer looks good.



Jan 28, 2013 at 08:59 PM
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