Resolution (Dpi) in print module

DxO PhotoLab
9

I print for other photographers and have to prepare images. What you are getting confused over is the mislabelling of resolution in pixels as dpi when it should be ppi.

Image resolution only applies to the image and is measured in ppi. Printers use dpi to define how many dots are laid down. Think about it - if one pixel was equivalent to one dot, how would you get one pixel that was anything other than the colours of the cartridges.

A 6000 x 4000 pixel image prints to 25" x 17" at 240 ppi, regardless of the printer resolution. What you get from higher dpi printers is smoother colours and gradients.

10

@Joanna’s printer has 180 nozzles for each of the c,m,y and k inks. 1440 dpi crams 8 times 180 nozzles into one inch. Multiply by 4 (colors) to get 5760 dpi. Combine with relative movements of paper an printhead to get whatever your print needs…

11

Printing more times with different colors on that place. Every color has its own nozzle on a different place.

From Irfanview, the printer window shows me the possibility to print the original size or different not original sizes. This printer is set to 600dpi so an image of 6000x4000 will become 10"x6.67". From what I remember it will print only 1 page filled with the top left part of the image.
I’m still not sure what happens with different sizes like “fit to page” or different dpi settings.
O yes, what I remember more was that when I send a picture with a setting request of 300 dpi and I print on the original size the printer will print an image of 20"x13.33" though the printer still prints on 600dpi. That’s a hardware property. What I still think, not sure, is that the image is resized to gain the demanded physical size with the native printer setting.

George

12

Thanks all for a flurry of responses. I’ll have another go.

Rob

13

Ppi is pixel per square inch, related to the native resolution of your camera sensor.
If you look at a bayer filter image on the web you see it’s 1/4 of the actual wells in a sensor. 1 pixel is one colorcode RGBL (l is your viewings device backlite strenght. Has nothing to do with exposure.)

DPI is dots per square inch. And because printers has diferent ways of making colors this can be a fox hole. Laser printers has tonerdots’s and the smallest toner partical is the smallest dot you can get. Office laserprinters do 600 and 1200 intepolair.
Because the paper moves and the laser writes only one line the horizonal and vertical resolution can differ. Laser is digital coded on/off( the optical layer on the drum and the lazerbeam diameter defines the maximum resolution and paperspeed is fixed(a minimum steps( resolution) by steppingmotor if you need a lower resolution it speeds up and the laser have more “off” moments.) together the give a square dpi resolution.
A inktjet can do much more overlay so that’s why a cheap 40 euro inktjet can give a nicer look then a 5000 euro laser printer of 600dpi which has more dot’s layed next to each other in threesomes and foursomes just in the right blend so you see one color while it is just dots.

Long story short.
If ppi< native dpi of printer,
1 no full paper and smaller image.
2 it add’s extra dots to fill the gabs between the dots.

If ppi> then native dpi of the printer.
The image will be compressed by the printer driver to fit the mechanical limitations.
So it’s no use to have more ppi sent to the printer then it’s native resolution can handle.
So the papersize influence the input resolution wile the printer on it’s max res keeps printing the same dpi.
Often is your develpper application a better place to balance this correctly. Scaling down is this called.
Scaling up means the source is smaller then the imaginary image in the printer.
Hence it add’s dot’s or scrink the image to fit 1:1.

Most printers can also print on a lower resolution then native and when you use a loup you see wider gabs and white paper.

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14

I normally use Apple’s own ColorSync Utiity to print externally from PL, having first exported to TIFF, resizing as required at 240ppi. I find this gives me more control and easier to use than the PL dialog.

I’ve just done a bit more research and found, in the manual, the print dialog with explanation.

I have a Mac and here is the print dialog for my printer :

Capture d’écran 2020-10-08 à 14.10.17
Capture d’écran 2020-10-08 à 14.10.17512×564 72 KB

As you can see, on my computer, the setting for dpi is labelled as Qualité and is in the Printer Configuration section of the dialog.

And here is a screenshot of the Windows dialog from the PL manual :

Capture d’écran 2020-10-08 à 14.18.15
Capture d’écran 2020-10-08 à 14.18.15816×435 301 KB

Here, you can see that the dpi setting is under the Printer settings section of the dialog.

This means that it is part of the printer’s behaviour and not part of the image itself. It refers to how dense you want the printer to lay down ink, (on mine) anywhere between “draft” quality and “SuperPhoto”.

If you are going to use the PL dialog to resize the image to fit on a particular size of paper, with certain margins, PL is going to choose a ppi that translates from the pixel size of the image to an area on the paper. This will be done totally irrespective of what quality dpi you choose for the printer.

Epson printers tend to have numbers like 1440, 2880, etc, whilst other manufacturers tend to base their printing resolutions on a multiple of 300. But I must emphasise that this has absolutely nothing to do with the finished size of the image on paper, purely the quantity of ink that gets laid down and the subsequent quality of colour and tonal variations in the final print.

When I print our photo club’s exhibitions, I tend to use “Superfin - 1440dpi” as a best compromise between quality and the amount of ink used and time taken to print.

As I said, I use an external printing utility and, thus, all images are prepared and sized on export at 240ppi to give me the required size to fit on the paper with the margins I want. Usually, for a landscape image, being printed on A3+ paper, to fit behind a mount board in a 50cm x 40cm frame, I export to TIFF with the longest side at 3638 pixels. This then fits (with a 2mm overlap) into an opening in the mount board of 380mm x 252mm. It’s extra work to use the external utility but, to my mind, when I am printing in bulk, for a specific frame size, it is a faster and easier workflow.

In summary, the dpi setting in the dialog is all about the quality of the printed image on a given paper surface; it doesn’t affect the image resolution or size, which, for you, using the PL dialog, will be calculated automatically as you choose the layout and margins you want on the paper size and quality of your choice.

Of course, the poorer the surface of the paper, the lower resolution (dpi) you will need, otherwise you can oversaturate the paper with ink, which not only looks horrible but, also, costs a lot more in ink :wink:

On your printer, I would suggest using 1200dpi on a photographic quality paper.

As for colour and sharpness, if you don’t have a colour-managed workflow, where you have created ICC profiles for your screen and printer, you will only be able to use pre-created printer profiles or let the printer make a best guess at the right rendering. This could mean that the print doesn’t look like what you see on screen and you might end up reprinting a couple of times before you are satisfied.

Bearing in mind the cost of paper, but especially inks, it really is worthwhile spending out on a calibration tool for both your screen and printer and spending time creating profiles, one for each ink/paper combination. Then you would choose to let PL manage your colour by setting the colour profile drop down to “managed by PL” and choose the profile of your choice

15

Shouldn’t that be dpi? :stuck_out_tongue_winking_eye:

16

Pixel/inch, not square inch. The same for dpi.

George

17

Look at the size of your tiff file. It doesn’t change when you change the dpi. That dpi is just a request to the printer to print that image as if that setting was used. So if you print original size, not my naming, and you have a setting of 300dpi and your printer prints at 600dpi then the image will be resampled 600/300=2 times to gain the same photo size when it would be printed on a 300dpi printer.

When the photographer sets the dpi field, he/she is wanting an explicit size of the picture. When using original size.
If you want a picture A3 just specify that, the driver is calculating the intermediary size of the image.
The qualification is telling something about the result of the print. But that doesn’t only depends on the dpi.

George

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18

This is simply not correct. As I said, exhaustively, in my previous post, dpi is everything to do with print quality and nothing to do with image size. The setting is under Printer Settings and does not affect the image size in any way. Please stop giving erroneous information to people who are struggling to understand the basics.

19

Ah too long back that theorie of this.( mm2 or inch2 looked ok but i think it’s 600x600 ppi so also 600x600 dpi.)
Are you sure? So it’s liniar x-as writing dots per inch which defines the resolution?
and no y-as, moving paper , dots per inch.
Sounds correct for a scanner that’s line by line with a multifunctional in ppi.
Doesn’t matter for the rest of the post.:grin:

20

Have a look. It’s very basic. Document size = amount of pixels/print resolution. As you can see the print resolution is expressed as pixel/inch. It’s Adobe.

The printer dialog in PL doesn’t let you to print in original size, only some pre-defined sizes. The resolution is showing the native resolution of the used printer. Calculation is done by the printerdriver.

George

21

For sure, it’s linear.
I still don’t know how the resizing i done.

George

22

i take your word for it! :smiley:

Out your link: (about downsizing and upscaling)

Bicubic Sharper (downsizing)

A good method for reducing the size of an image based on Bicubic interpolation with enhanced sharpening. This method maintains the detail in a resampled image. If Bicubic Sharper oversharpens some areas of an image, try using Bicubic.

Bilinear (upscaling)

A method that adds pixels by averaging the color values of surrounding pixels. It produces medium-quality results.

Better methode:

Bicubic

A slower but more precise method based on an examination of the values of surrounding pixels. Using more complex calculations, Bicubic produces smoother tonal gradations than Nearest Neighbor or Bilinear.

you can slow down writing speed on the drum (less lines/sec) so the papermovement has more time to transport between the writing lines. then you lower the y-resolution.

23

I refer to resizing when printing.
When taking pictures we deal with a exposure triangle. The exposure is determined by aperture, shutterspeed and iso. The same we have with printing: image dimension in pixels, print resolution in dpi or ppi, and document sizein inch. If we change one of them, at least one of the others has to be changed too. So let’s say I don’t want to resample but still want that specific document size. The only thing I can change is the print resolution. But what happens then, that’s what I don’t know. The printer print resolution can’t be changed, it’s hardware.So my idea is that some kind of resampling is done in the background. I’m not sure of this.

George

24

I remember a picture of a grave I took with text on it, shot under 45 degrees. Full size it was ok, just good. But when zooming out the text showed faults. I tried then to see the difference between printing that image when resampling to the right size based on the printers resolution and the other with let the printer do it. The last one was better.

George

25

Yes a printer can change it’s resolution.
By placing the dots wider of each other. Less dots is less resolution.
Resampling is deleting some of same color pixels in groups and replace, add more “space of nothing” on that same spot.
Only then is the size the same.

Other way around, a low ppi 100x100ppi causes bloks and zigzaged lines in the image if a 600dpi printer and the full size A4 is. Every 6st dot is a color.
I can show some examples made by a laser printer as in a office 600dpi colorprinter when i make some photo’s in different ppi export.
Printing on A4.
And use a paper loup to show the toner drops.

26

I’ve a brother color laserprinter, 600 dpi. I don’t use it for pictures.
And I have a HP Photosmart c309a. Also 600dpi. I can’t change it.

George

27

yesyes, already corrected in my post… :zipper_mouth_face:

28

We never have print resolution in ppi. Printers only know about dpi. They are dot devices, not pixel devices.

Only if you are talking about images, not printing here. Print scaling is different to resizing an image and can result in very poor results but it will only be printing the pixels in the document, just with more or less dots.

Certainly resampling is done but not at a pixel level, just the spacing between the dots.

I repeat - printers are dot devices, not pixel devices. But printers have software in them that manages the output quality, speed and distance between the dots. thus the idea of resampling, but not at a pixel level and changing the dpi of a printer does not change to size of the print.

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