image size

I am so confused. I thought i knew what I was talking about but i dont. I Have a K5, and I want to print out an image to 100cm by 70cm. How do i do it. Pixel size, thought it all made sense,resolution, seems pretty simple, but why is it that a 16mp camera will only give the dimensions of 55cm by 35cm image size??? And how is it possible that you can magically increase the image size and pixels on elements (does this decrease the quality for prints). I am so so so so so confused. Help!!!!!!!!!!!!!!!!!!!!!

Two ways in Photoshop.

1. Set the parameters in the crop tool to the size you want, at 300ppi for printing.

2. Alter the image size in the image size dialog (Image>Image Size) setting 300ppi as the resolution.

Photoshop will resample and create whatever size you want. Bicubic resampling is fine, but if you want to Bicubic Smoother for upsizing and Bicubic Sharper for downsizing for the web.

Visible to PU Plus members is a series of six short articles I did for the magazine that cover the very basics to get people "up and running" in a straightforward manner.

Further to the last post I made, don't forget when resizing that it's no use defining a print size that isn't the same aspect ratio as the image you want.

In that case you will need to make the image smaller than the paper size in one dimension so that all the image is included. There will be some blank area on the print that can be trimmed off.

This is what I'd probably do - (in the 'Image Size' command, within the 'Image' tab in my version of PS): Untick the 'resample image' check box and type in the image size you want, in cm. The resolution will adjust itself accordingly and as long as it's over 200ppi you're fine.

But if you want to retain the 300ppi resolution, leave the 'resample image' box ticked and select 'bicubic smoother' from the drop-down menu. Sharpen the image slightly before printing if you wish.

'Resampling' means interpolation - PS intelligently adds new pixels based on the existing pixels either size. This can reduce sharpness, hence my advice on sharpening.

Straight from the horses mouth so to speak...

http://www.adobe.com/designcenter/photoshop/articles/lrvid4289_ps.html

Simon

thanks guys all very helpful. I need to really experiment on large prints myself to really see these differences. It is definently one thing shooting digital to printing digital thats for sure.

However, if i were to print out a 16mp image at lets say a 100cm x70cm, my image resolution would end up resulting in 125ppi. After doing what is necessary in sharping and smoothing over as suggested, how bad would an image of this size really turn out?

If you leave the 'resample image' box checked, the image will still be 300ppi, albeit it will have been 'blown up' in photoshop using interpolation.

To check image quality, have a go printing it on A4 - leave the 'fit to paper' box unchecked in the printer and you will get an A4 sized portion of the overall image. Then put the image on the wall and see what it looks like, imagining it is part of a much larger print. Remember for big prints you will take a few steps back so don't be too critical of what it looks like close up

I took a pic at iso 200 and printed it at A2 after sharpening and contrast boost it was on a 12mp sensor and turned out fine with an expected little loss in detail(perceived) Dan

Interesting points. I am not sure how interpolation works, but i guess i will just have to try. Sabatini, a pro photo shop in Rome who have a quite professional printing service recommended me to increase the photo size to a stage where you hit a minimum of 100ppc. The said any smaller they won't do the print. I should recommend them this interpolation method and see what they say. Thanks all for the feedback

It's also worth remembering that you tend to view large prints from a greater distance, so the "apparent" quality stays about the same down to surprisingly low dpi. Modern interpolation techniques work pretty well. I'm particularly impressing with the Laczos3 setting in Serif PhotoPlus.

Al

Thanks for asking this question, you are not alone, in being confused by this.
I also cannot get my head around pixel size/pixel count, in relation to print size and ppi.
I have wasted so much printer ink and paper, without a decent print to show for it.

Having read all the replies to your question, which I am sure is very constructive advice, I am still totally confused.

You are correct, there is defiantly more to printing images than taking them.
I was completely at home in a darkroom with enlarger and trays of chemicals, but that was logical.

The next thing for me is to have a read of John’s, series of articles on this subject.

Take care.

glad my misfortune is of help to you. Basically to sum it all up from what i have learnt about this forum topic is what they say a standard photo should be printed at 240 dpi for exceptional image print quality. Standard digital slr's with lets say 16mp will get you a photo enlarged to 50cm x 30cm keeping 240 dots per inch. Obviously if you want to print bigger than that you 'll either need photo shop to increase the pixels for you, which i am not really that sure about, or just print bigger and end up with lets say 150dpi. In the end as mentioned early who's gonna look at the corner of a 1 meter large print for pixels, your gonna see the artwork from a distance.

Hows that for a conclusion to wrap up everyone's input?

It would be OK if accurate, but print resolution is normally 300ppi. Some printing houses specify different values and these should be adhered to for best results.

In practice, Photoshop resampling doesn't cause any particular woes if done withing reason.

Just to complicate things, for Projected Digital Images the image has to be:

Maximum horizontal dimensions: 1024 pixels
Maximum vertical dimensions: 768 pixels
Maximum file size: 900 kB
72 pixels/inch

this is so inter club competitions have a level playing field.


Regards