Large Prints ..

[bigdazzler]

If i have an image of approx 8.5MB (5000x2800 pixels) and want a print of approx 30x20, what ppi do i need ??

At 300, PS is telling me the image size is 16x9" , if I drop it to 150 ppi, it is telling me image size is 33x18"

Im a little confused, I dont normally print beyond about 18x12 (300ppi) so larger sizes im not real sure of.

Thanks in advance

[Calxoddity]

Daz,
I think if you tried something around 175dpi you'd be close - what you could do is adjust the dpi until you arrive at the desired output size. I assume this is being printed by a third party?

Regards,
Calx

[bigdazzler]

yea it will be mate .. i really wanna arrive at about 30x20 , so im wondering at what kind of dpi will i start to see a loss in IQ ?? So youre saying that 175 will be ok IQ wise ??

[I @ M]

Darren, have a read of http://www.ausphotography.net.au/for...ad.php?t=40702 the first image is the file resized for here, the second is a heavy crop from the third photo which is a 20x30 print hanging on the wall and shot through the glass in the frame.

Crappy old D200 10 mega pixels and uploaded to the printers as a jpeg at 300 dpi.

I am quite happy with the results at that size, as are others, so with your larger sensor on board the results will only be better.

[clcollins]

Daz,
If you read the tech help from your lab it will tell you. For prints I always use DPI 300 and have it sized to the dimensions I want. All of my print suppliers tell me 300 DPI is best... I thought you'd be able to set to 300dpi and then resize the image to 30x20 - that should work out right. It depends on what you are printing, if the image is of a person I wouldn't want to drop much below 300 due to skin tones etc.

[bigdazzler]

Thanks Andrew ,,, so I guess the output dimensions dont mean real much then ?? Because with these pixel dimensions and at 300ppi, it is telling me the image size is only 16x9 ?? Thats the bit that confuses me. You say you uploaded that image of the boat at 300 and your 30x20 seems to be really nice .. For me to get the PS image size anywhere near 30x20 I need to lower my ppi to 150 which then gives me 33x18

[Calxoddity]

Daz,
Here's a screen grab of a section of a page from the Epson Photo Print Guide (a 59-page document that you get on the CD with the r1900 and other printers), that talks about printer resolutions etc. This might be enough to get you heading in the right direction. Just to explain the colour coding: green is good resolution, red is overdoing it, yellow is acceptable. purple will have noticeable reduction in image quality, and pink resolutions are considered of insufficient quality to print.

(Mods - I believe this amount of use constitutes fair dealing for the purpose of copyright, but understand if this isn't okay...)

[JM Tran]

statistics and numbers will always be different than real world viewing Darren.

I print at 45x30 inch a lot for clients, and half the times the files are from 7-20mb per jpeg at 300 dpi.

results are great, remember its the viewing distance is whats important. A 30x20 inch will be more than easy.

[kiwi]

errr, I dunno, KISS, I just send everything thru to my lab at 300dpi. I dont change a thing apart from the crop.

[bigdazzler]

ok thanks all. Im not too concerned about it, I know I have plenty of pixels (25MP sensor)

I was just curious as to why PS was giving me 16x9 at 300ppi. I thought it would have given me a larger image size given the pixel dimensions.

[I @ M]

I am not sure of the process involved in resizing that the printers we use go to when our photos are uploaded. All we do is give them the whole file at 300dpi, tick the appropriate size box that we want them printed at and I guess their software does the sizing. Selecting a 20x30 in their program with the file from a 10mp camera ends up with their "quality indicator" warning us of reduced quality but so far we haven't seen any problems with the prints.

[bigdazzler]

which print lab are you using Andrew, if you dont mind ??

[Calxoddity]

Daz,
I don't know the answer to your last question re PS behavior in printing - I think it's telling you that if the desired/default output dpi is set to 300, this is as big as your print will go.

I have done some larger (but not as large as you are trying) in Aperture, where I've increased or decreased to dpi to come into optimal range.

Usually Aperture defaults to "best" dpi and shows you what the dpi result will be at intended output size. You can however change that. I had a 24MB scan that could have printed at almost 600dpi in A4, but I specifically selected 300dpi to reduce print time without sacrificing detail.

I also recall reading an article a month or two ago that said with poster-sized prints where the stand-off is intended to be a couple of metres, printing below 300 dpi to the low 200s will still result in a great print.

Now that I have the R1900 I'm itching to test the theory on some 42" panorama prints, but the cost of roll paper is the constraint at the moment!

Regards,
Calx

[bigdazzler]

Daz,
I don't know the answer to your last question re PS behavior in printing - I think it's telling you that if the desired/default output dpi is set to 300, this is as big as your print will go.

yea I think so too and thats the bit that was confusing me .. I expected to be able to go much larger at that ppi and those pixel dimensions.

Ah well, well send it off to the printers and see what happens

[Calxoddity]

yep - just divided 5000 and 2800 by 300, and it comes out as 16 x 9 (or near enough). So, if you want it bigger at 300dpi, you have to resize/resample the image to upsize it. Don't ask me about this though - I don't have PS and wouldn't have a clue of how to do it.

Regards,
Calx

[Bill44]

Not sure how it works in Photoshop but for export in Lightroom you set the physical size of the long side (in either inches or cm) and set the resolution at 300ppi and it resizes it.

[bigdazzler]

ok im at work now and working on my macbook .. I dont have any images from the A850 in this machine but I do have a few from my 10MP A300.

I just opened an image in PS which is 3872 x 2592 pixels, at 300 ppi , the "document" (print) size is 12x8.

If I then do as Bill says and enter 30" on the long side, the dialog box automatically resizes the short side to 20" and resamples the pixels to 9000 x 6025. So it seems it is adding pixels to achieve the desired print size at that particular ppi. This is all with the "resample image" check box ticked.

Now .. if I uncheck the "resample image" checkbox, and change the long side to 30", it again resizes to 20" on the short side but this time the pixels remain at the original dimensions (3872 x 2592) and the ppi drops down to 130ppi.

So 1. How does the resampling of the image (the adding of pixels) affect IQ ?? and 2. Is 130ppi too low for quality prints at that size (30x20) ??

Apologies if this is all basic stuff. Andrew (I@M) got me thinking about how a lot of our images are wasted sitting in computer hard drives and Id like to start printing a lot more of my stuff .. and im just trying to get my head around the best way to do it

[Bill44]

One thing that you need to bear in mind is the viewing distance that should be used for large prints. For example if you were to look at a roadside billboard at the viewing distance of a 6x4 print it would look hideous, and yet when you are driving past it can look quite sharp.

I have a mate who frequently does large canvas prints at 130PPI, and while canvas is a lot more forgiving than paper they look great.

At the PMA show in Sydney this year I viewed some absolutely huge prints, panormas 48"x 120", from the printers they were showing and up close they were a bit coarse, but viewed from about 4Metres they were magnificent.

[bigdazzler]

of course Bill .. i suppose im just wondering what an absolute minimum ppi resolution would be for something of that size, because you so often hear that print labs want a minimum of 240-300ppi for print files

[Bill44]

In conversation with the reps at the PMA show on this very subject the generally accepted minimum was 240PPI with 300PPI preferred. The reasoning being that, for example, it was far better to have an individual pixel split into say 4 pixels, rather than have a single pixel stretched to the size of 4 pixels, all to do with the preservation of detail.

It is very easy to see the similar reverse effect when you compare the same shot printed at 300PPI in 6x4 and 12x8, the 6x4 shot has lost a lot of detail due to the fact that 4 pixels have been crammed into 1.