Print resolution - again

[ahinterl]

I'd like to once and for all understand what programs like Lightroom and Photoshop do during printing.

Assume that I have an image of 1000x1000 pixels. There's no dpi, no ppi, no any other resolution defined, just the pixel size of the image.
Then, let's assume I have a Canon ip4950 printer. Maybe a bad example because you just know that the printer does 9600dpi, but you have no clue how many ppi's it has (i.e. the native "real" print resolution). Let's assume it does 600ppi (maybe that's even the truth?).

My understanding is that the term "ppi" refers to the number of "pixels" that the printer can place on paper within one inch. Each single "pixel" is a combination of one or more ink dots of different colors: The printer cannot mix ink, so it needs to place tiny dots close to others (it changes the pattern using "dithering") to form one "color pixel". Such a pixel is then what counts for the ppi resolution. So, the printer might be capable of doing 9600dpi, but since several dots are needed to form a single "pixel", we end up - in this example - with only 600 ppi. Ppi is not dpi :-)

Now, I want to print my image with all the resolution that my printer can do. I don't want to make my image a specific size, all I want is to get my image out of the printer with 1 pixel of my image = 1 printer "pixel" (knowing that 1 printer pixel is made of some dithered color dots). So, I don't care whether my printout would be poster or postage stamp size in the end.

Let's stay with Lightroom for now, though I guess in Photoshop it looks quite similar.

So, I call up Lightroom's print tab. Besides of the paper size - let's assume A4 - I can define the size of a singular rectangular area there which contains my picture. I have the respective info box activated, so in the print preview, I see an overlay of the size of the rectangular area as well as the resolution of the image contained within. Let's assume I see "272,217 x 204,4 mm @ 428 ppi" there: I have my Image centered on the A4 paper in landscape mode and sized so it almost fills the paper from top to bottom. Nevertheless the're white borders left and right of the image, and small white borders at the top and the bottom.

From what I see I would conclude that if I would print this out, the resolution capabilities of my printer would exceed the resolution of my image: I see 428ppi in Lightroom, and I know my printer can do 600ppi.
So, as a consequence, I would make the rectangular area in Lightroom smaller, in other words, I would shrink my image until the info box reads "...@600ppi". That's what I'd assume as being the "right" resolution because it matches the printer ppi exactly. Sure, I'd have much more white borders around my image, but I don't care.

That's my theory. On the other hand, I have read things such as that printer drivers do their own thing regardless of the resolution of the image sent to the printer etc. etc.

And, there's that "print resolution" check box and input value in Lightroom. My explanation for this:

As I have described above, Lightroom seems to be incapable of just taking an image file of size x,y and put it on the paper as it is. Instead, it puts that paper into a rectangular area of which I myself need to define the size. Since the size of the box is measured in length units and not in pixels, there's no connection between my image size x and y and the width and heigth of that box. In other words, I cannot size the box exactly the size of my image (in pixels). I need to work around this more bad than good by taking the image ppi and kind of estimate the printer ppi if I don't know it - the process I described above.

If I now activate the "print resolution" check box, I add another level of complexity to the print process: I force the printer to use a specific ppi instead of the one that Lightroom already calculated. So, in my example, if I set the "print resolution" to 500 ppi, this would be more than the 428 ppi Lightroom is giving me. What Lightroom or the printer do in this case I don't know, but I suspect a process called "upscaling" would be invoked: Since there's no more image information that 428ppi, Lightroom needs to interpolate to fill the gap to 500ppi.

Question: Am I correct with the perception that I have, or where does my model need corrections, and does someone have links to resources with explanations?

Andreas

[Tony Jay]

You seem to have a fair bit knowledge.

The question that I have for you is this:

Do you really want to know exactly what is going on  under the hood or are you just trying to use the software (LR or PS)?

Depending on the answer myself or others will have a better idea of what you really need to know.

Regards

Tony Jay

[ahinterl]

Tony, I'd really like to know what's going on "under the hood" - understanding is key for me. Stupid usage of programs without knowledge is not my thing.

Andreas

[ErikKaffehr]

Hi,

The printer has a native resolution. Let's assume 600 PPI. You are right about the way pixels are created, it is called dithering.

Normally you would define the print size. If you also give PPI Lightroom will use a combination of "bicubic interpolation" variants to resize the image to that PPI. If this interpolation is not done the printer driver will do the rescaling. It may do it better or worse. Jeff Schewe says LR does it better. I'd expect the differences to be quite subtle.

I'd suggest that there is little reason to print at native PPI.

Best regards
Erik

I'd like to once and for all understand what programs like Lightroom and Photoshop do during printing.

Assume that I have an image of 1000x1000 pixels. There's no dpi, no ppi, no any other resolution defined, just the pixel size of the image.
Then, let's assume I have a Canon ip4950 printer. Maybe a bad example because you just know that the printer does 9600dpi, but you have no clue how many ppi's it has (i.e. the native "real" print resolution). Let's assume it does 600ppi (maybe that's even the truth?).

My understanding is that the term "ppi" refers to the number of "pixels" that the printer can place on paper within one inch. Each single "pixel" is a combination of one or more ink dots of different colors: The printer cannot mix ink, so it needs to place tiny dots close to others (it changes the pattern using "dithering") to form one "color pixel". Such a pixel is then what counts for the ppi resolution. So, the printer might be capable of doing 9600dpi, but since several dots are needed to form a single "pixel", we end up - in this example - with only 600 ppi. Ppi is not dpi :-)

Now, I want to print my image with all the resolution that my printer can do. I don't want to make my image a specific size, all I want is to get my image out of the printer with 1 pixel of my image = 1 printer "pixel" (knowing that 1 printer pixel is made of some dithered color dots). So, I don't care whether my printout would be poster or postage stamp size in the end.

Let's stay with Lightroom for now, though I guess in Photoshop it looks quite similar.

So, I call up Lightroom's print tab. Besides of the paper size - let's assume A4 - I can define the size of a singular rectangular area there which contains my picture. I have the respective info box activated, so in the print preview, I see an overlay of the size of the rectangular area as well as the resolution of the image contained within. Let's assume I see "272,217 x 204,4 mm @ 428 ppi" there: I have my Image centered on the A4 paper in landscape mode and sized so it almost fills the paper from top to bottom. Nevertheless the're white borders left and right of the image, and small white borders at the top and the bottom.

From what I see I would conclude that if I would print this out, the resolution capabilities of my printer would exceed the resolution of my image: I see 428ppi in Lightroom, and I know my printer can do 600ppi.
So, as a consequence, I would make the rectangular area in Lightroom smaller, in other words, I would shrink my image until the info box reads "...@600ppi". That's what I'd assume as being the "right" resolution because it matches the printer ppi exactly. Sure, I'd have much more white borders around my image, but I don't care.

That's my theory. On the other hand, I have read things such as that printer drivers do their own thing regardless of the resolution of the image sent to the printer etc. etc.

And, there's that "print resolution" check box and input value in Lightroom. My explanation for this:

As I have described above, Lightroom seems to be incapable of just taking an image file of size x,y and put it on the paper as it is. Instead, it puts that paper into a rectangular area of which I myself need to define the size. Since the size of the box is measured in length units and not in pixels, there's no connection between my image size x and y and the width and heigth of that box. In other words, I cannot size the box exactly the size of my image (in pixels). I need to work around this more bad than good by taking the image ppi and kind of estimate the printer ppi if I don't know it - the process I described above.

If I now activate the "print resolution" check box, I add another level of complexity to the print process: I force the printer to use a specific ppi instead of the one that Lightroom already calculated. So, in my example, if I set the "print resolution" to 500 ppi, this would be more than the 428 ppi Lightroom is giving me. What Lightroom or the printer do in this case I don't know, but I suspect a process called "upscaling" would be invoked: Since there's no more image information that 428ppi, Lightroom needs to interpolate to fill the gap to 500ppi.

Question: Am I correct with the perception that I have, or where does my model need corrections, and does someone have links to resources with explanations?

Andreas

[Tony Jay]

Eric's reply is useful for several reasons.

Firstly there is no standard print size on paper for a standard dimension of pixels in a JPEG or Raw file or whatever.
This is an important principle to grasp.

A practical example comes to mind:
Yesterday I printed a large panorama, in this case, on a 24" roll with my Epson Pro 7900. The print was 50" long and 22" high.
I have also printed this same file several times on smaller format paper.

Based on suggestions from Jeff Schewe (LuLa's own Camera to Print and Screen is a fantastic resource by the way) I check the native resolution at the size I want to print. Doesn't matter what size medium one is printing on size the image appropriately to your taste. If the native resolution is less than 360 (on an Epson - different rules for HP and Canon: use 300 in this instance) then set the resolution in LR to 360 to allow upsampling. If the resolution is greater than 360 (300 with Canon and HP) then upsample to 720 (600 with Canon and HP).

With the largest print I have made of the panorama the native resolution was 240-ish and so I upsampled to 360. All the others were upsampled to 720. Were I to print this panorama on 44" roll paper then the native resolution would reduce to somwhere between 120-180. I would upsample this to 360 as well. Would one see a difference in resolution with a short viewing distance? Perhaps, but such large prints need a longer viewing distance so in fact lower resolution prints of that size are very acceptable.

Regards

Tony Jay

[ahinterl]

Thank you, got this source which helped a lot: http://www.digitalphotopro.com/technique/workflow/the-right-resolution .html

Looks like printing the way I want is an absolute exception and nobody really does it this way. That explains why programs like Lightroom or even Qimage don't offer an option to place images on a page using their native sizes (Qimage seems to be able to place one image on one page, but not mutliple images arranged at one page where all images retain their native sizes).

Printing is like that: You have paper of a certain size, or want to have your images in a specific size on paper. So, you size your images to fit the desired dimensions. Not the other way round. In this, the normal case, I guess that almost all printouts will have some kind of resampling being performed.

Guess I'll test Qimage which promises to give the best results, don't know if Lightroom 4 is comparable.

Thank you for your help.

Andreas

[Tony Jay]

More to come:

It is far better to let LR do the upsampling than the printer driver.
The process in LR is somewhat intelligent as it changes the process depending on the degree of upsampling required.
Jeff Schewe is the resource to explain the exactitudes of the process although others such as Eric Chan and Andrew Rodney probably understand it really well.

The process by which the printer lays down ink is strictly proprietary but the principles of the dithering process as elucidated by you are basically correct and widely understood. Although the look and apparent quality of the print is determined to some extent by the dithering process as well as maximum resolution that a particular printer can deliver for practical purposes the maximum resolution can rarely be appreciated.
It is possible that the last paragraph is not well expressed so others might want to correct any apparent misconceptions - I didn't get much sleep on the weekend (and I wasn't partying!).

Regards

Tony Jay

[Bart_van_der_Wolf]

The printer has a native resolution. Let's assume 600 PPI. You are right about the way pixels are created, it is called dithering.

Indeed. Upon request, the printer driver can send the native resolution it expects to a software application. This is e.g. used by an application such as Qimage.

Normally you would define the print size. If you also give PPI Lightroom will use a combination of "bicubic interpolation" variants to resize the image to that PPI. If this interpolation is not done the printer driver will do the rescaling. It may do it better or worse. Jeff Schewe says LR does it better. I'd expect the differences to be quite subtle.

I'd suggest that there is little reason to print at native PPI.

I tend to disagree with that, also based on earlier tests reported here on LuLa. If I remember correctly, one of those tests showed visibly lower resolution for 359 PPI image data sent to a 360 PPI driver setting. Another improvement can be achieved by sharpening at the output size. It is counterproductive to first sharpen and then resample to a larger size.

How much the image improves will depend on several factors incuding image content, but the image will not become worse when printed at the native resolution because no interpolation is needed. The quality of resampling of course also makes a difference, but printer drivers are not known for their resampling quality, so whenever resampling is required (with subsequent sharpening), it's best left to quality software. IMHO, of course.

Cheers,
Bart

[dgberg]

Sort of the same topic.

We never hear too much about about resampling vs. upsampling.
The resample should always be better and creates more detail and sharpness from the original.
Where as the Lightroom upsample only creates more resolution.
At what point do you stop your resample(Say at 180 instead of 240) to control file size and then pickup a little more resolution in Lightroom with the upsample to 300 or 360?
Where does this all equal out if it indeed does?

[Scott Martin]

Everyone should do exhaustive testing and come to their own conclusions. One's source files and perception will make all the difference. It takes very rare images to show significant differrences between these higher resolutions.

FWIW, I have continued to evaluate and reevaluate this issue for over 20 years now and am currently using LR to sample everything to 480ppi for printing on both Epson and Canon printers. I have seen good reason to go with 480 ppi over 400, 360, 300, etc and have yet to see benefit from going higher. Just my $0.02!

[mgrayson]

I just made prints on an Epson 3880 at 240, 360, and 720ppi from a file with ~400ppi resolution at the print size. With a loupe, there is a clearly less definition in the 240ppi print, but the 360 and 720 prints are identical as far as I can tell. In LR4, letting the software handle everything.

Interesting!

--Matt

[Scott Martin]

I just made prints on an Epson 3880 at 240, 360, and 720ppi from a file with ~400ppi resolution at the print size. With a loupe, there is a clearly less definition in the 240ppi print, but the 360 and 720 prints are identical as far as I can tell. In LR4, letting the software handle everything.

Good - keep testing with different images at more resolution increments. I think you will eventually run into images that will see benefit from the difference between 360, 400 and 480ppi.

[Bart_van_der_Wolf]

I just made prints on an Epson 3880 at 240, 360, and 720ppi from a file with ~400ppi resolution at the print size. With a loupe, there is a clearly less definition in the 240ppi print, but the 360 and 720 prints are identical as far as I can tell. In LR4, letting the software handle everything.

Interesting!

Hi Matt,

Above 360 PPI on an Epson printer, make sure you select the "finest detail" option in the printer driver, otherwise it will downsample to 360 PPI.

Cheers,
Bart

[mgrayson]

Hi Matt,

Above 360 PPI on an Epson printer, make sure you select the "finest detail" option in the printer driver, otherwise it will downsample to 360 PPI.

Cheers,
Bart

Ah! I hadn't realized that. Reprinting with "finest detail" checked yields a slight, but clearly visible (with 8x loupe) improvement. Since the file was ~440 ppi, this isn't surprising.

Does 1440 dpi vs 2880 dpi matter here? I got some ink smearing on the edge of the print the one time I tried 2880.

Matt