Doug Kerr
Well-known member
Recently I replied to an inquiry by Kevin Carter in the ProPhoto Home forum regarding the significance of the resolution indicator(s) in an image file. The thread morphed into a discussion of the requirements/recommendations for file image resolution presented by various printing labs as part of their guidelines for clients.
At one time, these were (although not always clearly stated) cast in terms of the resolution indicator(s), a complete bum steer.
Today, though, the information is usually (although not always clearly stated) in terms of resolution (pixels/in) of the image file as reckoned at the size of the print to be made. The "recommendations" often include one or more of the following:
a. A desirable general resolution value, evidently conditioned on the assumption that a file of lower resolution will not produce a visually-good print of the size of interest. (Often 300 px/in is cited.)
b. An optimal resolution value, generally corresponding to the "native input resolution" of the printer chain to be used for prints in that size range. (MpixPro gives 250 px/in for this for all print sizes they offer.)
c. A "minimum" resolution, evidently conditioned on the assumption that a file of lower resolution will not produce a visually-acceptable print of the size of interest. (Perhaps 100 px/in is cited.)
It would at first seem that criterion (b) makes sense insofar as absolutely avoiding any need for interpolation to be done at the lab, rendering moot any issues about what interpolation algorithm might be used.
But there may be a wrinkle. MpixPro, for example, points out that because of small uncertainty in the lateral tracking of the paper web in their printers, they prepare the image for printing at an inch size about 1.5%-1.7% greater than the dimensions of the ordered print (and it "bleeds").
So if the user interested in an 8" x 10" print diligently resizes it to 2000 x 2500 px, at the lab it will be upsized to about 2030 x 2538 px (probably by part of the lab's pre-press processing system) before presenting it to the "native resolution" interface of the printer chain. Now I don't know whether that kind of upsizing is especially trivial or especially challenging - my guess is the latter.
A fundamental issue of discussion in this area compares two approaches to a situation in which the "original" image file (perhaps an edited crop of the camera original, presumably with an aspect ratio matching that of the print to be made) has pixel dimensions substantially smaller than those implied by the "recommended" resolution as applicable to the desired print size:
a. The user upsizes the image (using his choice of processing software, perhaps choosing among various offered interpolation algorithms and/or parameters) to the pixel dimensions implied by the "recommended" resolution as applicable to the desired print size, and sends that image file to the printing lab.
b. The user sends the image file as is to the printing lab.
It is often heard that (a) is the superior workflow in terms of getting the "best" print.
My question is, why?
Possibilities would seem to include:
1. The software used by the commenter is more sophisticated than that built into the pre-press processing system of the specific (or typical) lab, and thus generally or often results, under scenario (b), in a "better" (more visually-appealing?) print.
2. The software used by the commenter offers the user the opportunity to choose among different interpolation algorithms, and/or to adjust various of their parameters, so that the user can optimize the process to the nature of the scene, or the use to which the print will be put, thus leading, under scenario (b), to an especially "good and appropriate" print.
3. Something I never thought of.
I have almost no personal experience in this matter, When I have an image printed in a "lab", it is usually because I need a large "poster". I always follow scenario (b).
So what can you guys who deal with this matter regularly and in a demanding context tell me about this matter? If you do (a), what software do you use? And do you indeed sometimes switch interpolation algorithms or parameters to best suit the specific task at hand?
Thanks.
Best regards,
Doug
At one time, these were (although not always clearly stated) cast in terms of the resolution indicator(s), a complete bum steer.
Today, though, the information is usually (although not always clearly stated) in terms of resolution (pixels/in) of the image file as reckoned at the size of the print to be made. The "recommendations" often include one or more of the following:
a. A desirable general resolution value, evidently conditioned on the assumption that a file of lower resolution will not produce a visually-good print of the size of interest. (Often 300 px/in is cited.)
b. An optimal resolution value, generally corresponding to the "native input resolution" of the printer chain to be used for prints in that size range. (MpixPro gives 250 px/in for this for all print sizes they offer.)
c. A "minimum" resolution, evidently conditioned on the assumption that a file of lower resolution will not produce a visually-acceptable print of the size of interest. (Perhaps 100 px/in is cited.)
It would at first seem that criterion (b) makes sense insofar as absolutely avoiding any need for interpolation to be done at the lab, rendering moot any issues about what interpolation algorithm might be used.
But there may be a wrinkle. MpixPro, for example, points out that because of small uncertainty in the lateral tracking of the paper web in their printers, they prepare the image for printing at an inch size about 1.5%-1.7% greater than the dimensions of the ordered print (and it "bleeds").
So if the user interested in an 8" x 10" print diligently resizes it to 2000 x 2500 px, at the lab it will be upsized to about 2030 x 2538 px (probably by part of the lab's pre-press processing system) before presenting it to the "native resolution" interface of the printer chain. Now I don't know whether that kind of upsizing is especially trivial or especially challenging - my guess is the latter.
A fundamental issue of discussion in this area compares two approaches to a situation in which the "original" image file (perhaps an edited crop of the camera original, presumably with an aspect ratio matching that of the print to be made) has pixel dimensions substantially smaller than those implied by the "recommended" resolution as applicable to the desired print size:
a. The user upsizes the image (using his choice of processing software, perhaps choosing among various offered interpolation algorithms and/or parameters) to the pixel dimensions implied by the "recommended" resolution as applicable to the desired print size, and sends that image file to the printing lab.
There, because the recommended resolution may not precisely correspond to the native resolution of the printing system to be used, or perhaps because of the "expansion" issue I spoke to above, the image may be resized before being presented to the printing chain's "native" interface, this probably being done by software that is part of the lab's pre-press processing system.
b. The user sends the image file as is to the printing lab.
There, the image will be resized before being presented to the printing chain's "native" interface, this probably being done by software that is part of the lab's pre-press processing system.
It is often heard that (a) is the superior workflow in terms of getting the "best" print.
My question is, why?
Possibilities would seem to include:
1. The software used by the commenter is more sophisticated than that built into the pre-press processing system of the specific (or typical) lab, and thus generally or often results, under scenario (b), in a "better" (more visually-appealing?) print.
2. The software used by the commenter offers the user the opportunity to choose among different interpolation algorithms, and/or to adjust various of their parameters, so that the user can optimize the process to the nature of the scene, or the use to which the print will be put, thus leading, under scenario (b), to an especially "good and appropriate" print.
3. Something I never thought of.
I have almost no personal experience in this matter, When I have an image printed in a "lab", it is usually because I need a large "poster". I always follow scenario (b).
So what can you guys who deal with this matter regularly and in a demanding context tell me about this matter? If you do (a), what software do you use? And do you indeed sometimes switch interpolation algorithms or parameters to best suit the specific task at hand?
Thanks.
Best regards,
Doug