Printing Images.

[ultramol]

Could anyone tell me , if ccd cameras have such a small amount of pixels how do you get to print  say A4 size prints from the original, which I generally print at 360dpi. Do you just use interpolation and if so won't that be pushing it a bit to far... Thanks....Geoff

[frugal]

An A4 sheet is about 11x8 inches. So at 360 dpi you want an image of 4000x3000 ish.

So you have two alternatives:

1 - reduce the dpi to fit a single image onto a page. A 1280x1024 image will be about 80dpi.

2 - create a 4x4 mosaic from multiple images

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[pete_l]

Considering that an LCD doesn't have a 360 dpi resolution, and images look perfectly fine on that, I'd suggest lowering your print resolution.

My 1920x1080 monitor has a horizontal screen size of 20 inches: 96 DPI and the image quality is perfectly acceptable.

This is a pub-discussion I've had with a semi-pro photographer friend. He insists that ALL prints MUST be 300 DPI or better. However in practice people view larger prints from further away, so if you want large prints, bear in mind that your viewers won't be getting right up, close, to it. So the resolution doesn't need to be that high.

[glappkaeft]

The only way to be sure that you'll be happy with the end result is to do a series of small test prints with different dpi. However just like Pete I have noticed that larger prints can get away with smaller dpi if necessary so the test prints represents the worst case.

The test prints will also tell you if the colour calibration is off or if the printer auto-"optimises" your images. I have had a large moon print (32x48 cm / 2000x3000 pixels) ruined by a heavy automatic contrast "enhancement".

[ultramol]

Thanks for this input. I have been a keen amateur photographer for 45 years and have yet to take any astro photographs except through an eye piece,( its my ambition to rectify this hence the question I posed)  . But even if you reduce the print dpi to say 240 the resulting image will be soft. Its quite acceptable for a screen to be 72dpi but this would just give a very blocky enlargement if printed at this. A mosaic sounds the most reasonable solution, or a very big chip in an imaging camera but I would expect them to be expensive. Years ago in photoshop interpolation was hit and miss and I used to enlarge by the 10% method but now in cs5 the algorithms are superb and its surprising what you can get a way with. Also sharpening is now a lot better so selective sharpening will, I suppose , help in this matter. Some of the lunar images on this site are as sharp as a needle and these are the sort of images I hope to learn to do , with your help, Just got to get my equipment now and start shooting. Thanks once again....Geoff

[Jannis]

What i've personally noticed, is that on smaller prints, say 10-15cm, i need higher DPI, as i usually look more closely at them. While an A4 print for example, is usually observed from a bit of distance, and is therefor not as critical. But of course, if you want high resolution prints, then you either need a high resolution sensor, do a mosaiq, or alternatively do a drizzle stacking, wich can increase the resolution significantly.

[ultramol]

Thank you Jannis, now for my next question ! What is a drizzle stacking ? It sounds intriguing.

[frugal]

The dpi also depends on what you want the print for. The front cover of a coffee table book or a quality print hanging on a wall have different dpi requirements to a photo in a newspaper or a blog.

If the original poster has been a keen photographer for 45 years then he (and his photographic collegues) are likely to have higher standards in the print quality. In the same way that experienced astrophotograhers here fuss about slight star trails in a photo or woodworkers fuss about tight fitting joints. They are things that others might not notice, but you do , so they are important.

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[Jannis]

Drizzle is basically upsampeling the resolution using multiple images.

You can read a little more about it here: http://deepskystacker.free.fr/english/technical.htm#Drizzle

[Guest]

The ideal distance to view a photo from is equal to the diagonal size of the image (cant remember where I read that).. Photographers print at 300dpi but you can easily get away with less.  There is a trick in Photoshop where you can increase the size of an image with almost no image degradation:

On the menu go Image \\ Image Size

Set the increase in size to 10%

Set the Interpolation to Bicubic Smoother

Press OK

[Guest]

PS I created an action with this (ie a macro) and assigned it to F10 key then just repeatedly press F10 to upscale an image

[ultramol]

Thanks for your thoughts and thanks for the link jannis

[ollypenrice]

People from the print and daytime photography world don't always understand astrophotos. Firstly we are resolution limited by the seeing and, secondly, we are dealing with absurdly small amounts of light. We can cut ourselves a bit of slack, therefore. We are using telescopes, not microscopes.

In preparing an image for print I'd advise lifting the low values in Curves and ignoring the increase in noise, which will not be resolved in a print copy anyway. (Loss of resolution's positive side!)

The magazines generally ask for 200DPI or thereabouts.

Olly

[ultramol]

As much as I love taking pictures I also like the PS side aswell. Hopefully it wont be long now before I start taking astro images and then work on them in photoshop. Some of the lunar pix are outstanding, it looks as though you are about to land on the surface ! If I get anywhere near to them I will be very happy indeed.