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Hi Guys,

So I recently tried to print out one of my images to give as a gift to some friends and family using snapfish, a UK based printing company. On the first attempt that they tried I was very unimpressed with the resolution and print quality. They gave me a refund, but I am now looking to see what I can do to improve the image quality. I feel like something somewhere has gone wrong in the way that I have processed, scaled or sized the image. I am not too sure. I use photoshop and usually when everything is viewed digitally compression and quality doesn't matter as much compared to printing. When I export the image as a jpeg even at maximum quality selected the image file size will go down to 3mb the original tif file is 56.9mb, so that does seem like a significant reduction in quality.

 

I have attached the base tif file here, if anyone could provide some guidance that would be great. 

 

Best,

SHO 2.tif

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A lot of online print shops are not expecting astrophotography type pictures, so they often do some post-processing themselves on the pictures that you upload.

You need to look for an option in the upload (if they support it), that the photo has already been post-processed and you want it printed as-is.

If your print provider does not allow this then I can recommend CEWE Photoworld - I have used them in the past, and using their free software I have found that the results of the print were as the photo looked in their software.

I think you can use them without downloading their software, but it is easier to use with the software (which apparently supports MacOS, Linux & Windows, I think).

Edited by gilesco
typo, software OS support
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Hi thanks for that. I will have a look at them for sure. Sadly for this particular image I have to  use Snapfish as they gave me credit rather than a full cash refund. 

 

Funnily enough I do know that Snapfish can produce good quality images sometimes as they have done some for me in the past it's seems to be a problem with this particular image. 

 

Best,

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19 minutes ago, 5haan_A said:

Hi thanks for that. I will have a look at them for sure. Sadly for this particular image I have to  use Snapfish as they gave me credit rather than a full cash refund. 

 

Funnily enough I do know that Snapfish can produce good quality images sometimes as they have done some for me in the past it's seems to be a problem with this particular image. 

 

Best,

Looks like Snapfish only allows you to upload files to a certain size, the nice thing about CEWE is that you are editing offline, so I just load my TIFF to the software (sometimes 500Mb in size) and I can work with it unadulterated, then once the photo type & size are set it uploads the pixels exactly as I see in the software for printing, making sure of the following option:

image.png.0aa01e78df0610739deb266da012c88d.png

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What exactly were you not pleased with?

What was the DPI of your print?

Minimum that you should go with is 300dpi, and use 600dpi if you can.

Size of your image is roughly 2500 x 2000. If you used 300dpi to print, this would make it 8.333" x 6.666" or about  21.16 cm x 17cm. That is about A5 sheet of paper size. That is rather small and this is lowest resolution that you should use for printing.

With 600dpi - you are looking at a6 or post card size.

How large did you want to print it?

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If you're trying to print larger, you could try step interpolation in photoshop, it's not magic but if you increase the image size by about 5% in steps it can work quite well.

Don't forget that if it's big, people will usually stand further away so it needn't be perfect ?

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I use https://dscolourlabs.co.uk/; their metallic prints. I took images I wanted to give as gifts, created four versions with different brightness and contrast levels, and combined them into a single image. Sent those off and got a small trial print. From that test image, I could pick the version that I felt worked best and get however many larger versions I wanted. 

I was happy with the result and so was my family.

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On 01/10/2020 at 13:12, vlaiv said:

What exactly were you not pleased with?

What was the DPI of your print?

Minimum that you should go with is 300dpi, and use 600dpi if you can.

Size of your image is roughly 2500 x 2000. If you used 300dpi to print, this would make it 8.333" x 6.666" or about  21.16 cm x 17cm. That is about A5 sheet of paper size. That is rather small and this is lowest resolution that you should use for printing.

With 600dpi - you are looking at a6 or post card size.

How large did you want to print it?

I think this was what my problem is. The size I printed was A3 size which explains why the quality of the print was so poor. 

 

21 hours ago, knobby said:

If you're trying to print larger, you could try step interpolation in photoshop, it's not magic but if you increase the image size by about 5% in steps it can work quite well.

Don't forget that if it's big, people will usually stand further away so it needn't be perfect ?

I think this is a really important thing to think about because I do want to print bigger in the future. What would be good on my part is to get a good understanding of how I can create big pictures. As Vlaiv said the size of my image is 2500x2000 at 300 dpi that translates to 21.16cm x 17cm. How would I go about doubling or tripling the size of my image without sacrificing a massive amount of quality? I do think A3 is a good size for a print, A4 at a minimum. I will try the interpolation method you suggested as an option.

 

20 hours ago, old_eyes said:

I use https://dscolourlabs.co.uk/; their metallic prints. I took images I wanted to give as gifts, created four versions with different brightness and contrast levels, and combined them into a single image. Sent those off and got a small trial print. From that test image, I could pick the version that I felt worked best and get however many larger versions I wanted. 

I was happy with the result and so was my family.

I will check them out. It's nice being able to share our hobby in this way with friends and family. 

 

Best,

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10 minutes ago, 5haan_A said:

I think this is a really important thing to think about because I do want to print bigger in the future. What would be good on my part is to get a good understanding of how I can create big pictures. As Vlaiv said the size of my image is 2500x2000 at 300 dpi that translates to 21.16cm x 17cm. How would I go about doubling or tripling the size of my image without sacrificing a massive amount of quality? I do think A3 is a good size for a print, A4 at a minimum. I will try the interpolation method you suggested as an option.

One thing to remember is that the 300 dpi "rule" is from the days of glossy magazines. And really only applied to those sorts of people who listen to HiFi's in order to try and discern the hiss, crackles, pops and other faults.

Consider the resolution of your monitor. Even a large one (70cm across, not diagonal) gives a perfectly acceptable resolution at 1920 pixels per line. That is 70 DPI.

The reason is that the larger a screen is or the larger a print, the further away a person views it from. I get poster size photos printed at 100 DPI and they come out as good as I would ever wish for. It may well be that if a person scrutinised one from right up close, they might see a little pixelation, but nobody ever does :)

 

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A lot also depends on the surface, we had an Acrylic and Aluminium 12"x12"  print from photobox (I think) the gloss of the Acrylic was much preferred over the almost matt/semisheen Aluminium. 

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DPI for printing is much more complex than the 'use 300dpi' usually offered.

300dpi is the general rule for books and magazines etc. that will be viewed at a comfortable reading distance. At A4 that's an image about 3600 x 2400 pixels (~8Mp). This effectively gives you what Apple calls a 'retinal display' - that is the resolution is roughly that the eye can perceive so you don't see any artefacts and maximum usable detail is presented. In practice, we often interpolate images to get this resolution (one of my roles is a magazine editor) and it's surprising what you can get away with. Photographers are often astounded that 8 megapixels is plenty for the cover of a normal UK magazine (perhaps not Vogue or National Geographic...)

For images to be viewed at greater distances lower DPI can be fine, for example a typical pullup display may be printed at 300dpi but the pre-interpolated image may well below 100dpi and still look fabulous at a normal viewing distance. On the other hand I have produced artwork for interpretation boards and used ~600dpi for the component images and downsampled to 300dpi for the final artwork, as it would be viewed close up.

Ideally I would aim for about 150dpi multiplied by the viewing distance in metres, but you can go lower than this. For example, many desktop computer screens used to be 90 dpi but images looked fine on them at about 1 metre distance.

The problem with most astro images is that they are often oversampled already with the finest detail being 2 or 3 pixels. They normally look fine as they are lightly blurred rather than pixellated, but it does mean they can look mushy and soft when blown up.

One trick we often use in the magazine is to resample an image with interpolation and then apply a judicious amount of sharpening (usually just unsharp mask, but sometimes deconvolution) to bring definition to the sharp edges in the image which creates the illusion of higher resolution. This suits the sort of  images we have which are typically machines etc. but may not work as well with 'organic' shapes like people or nebulas!

Another tip is to view your image at 100% on your computer screen i.e. one pixel per screen pixel. This allows you to 'lean in' a bit and make a fair judgement of how sharp it really is.

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My computer screen is 23" diagonal and has 96dpi. Mobile devices have very high DPI count and there is even named scale of different pixel densities:

image.png.380141a01fe318c5ca05dffef0903694.png

Screens produce their own light and that is quite different then reflected light of a print. Higher contrast can be obtained from display device than from print.

In any case, we can see what sort of resolution human eye supports. We resolve at best about 1 arc minute. Let's say that minimum viewing distance is 50cm. How small single dot should be in this case?

At viewing distance of 500mm (that is 50cm), 1 arc minute feature equals to 0.14544mm or if we want to get that to DPI 25.4mm / 0.14544 = 174 DPI.

For viewing distance of 30cm - which is "reading" distance, we thus need ~290DPI (174 * 50 / 30). This is why we say we need at least 300dpi for printed material.

Would 100dpi be sufficient? Well, yes if you have something that can be only viewed at 873.19mm distance or 87cm away, but bear in mind - people want to get close to these sort of images to better see the detail.

Your best bet is to aim for reading distance - around 30cm and go for at least 300dpi.

How to get such image and what sort of FOV can we expect here?

Key to creating large size image with smaller sensor is - making mosaic.

At best, one should go for 1"/px - higher than that will be oversampling. This translates into 5 arc minutes per inch.

Want to fill A3 print? You will need:

11.7" x 16.5" = 3510px x 4950px = 58.5' x 1° 22.5'

You have about 1.3 degrees x 1 degree - not very large FOV.

 

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On 01/10/2020 at 11:25, 5haan_A said:

Hi Guys,

So I recently tried to print out one of my images to give as a gift to some friends and family using snapfish, a UK based printing company. On the first attempt that they tried I was very unimpressed with the resolution and print quality. They gave me a refund, but I am now looking to see what I can do to improve the image quality. I feel like something somewhere has gone wrong in the way that I have processed, scaled or sized the image. I am not too sure. I use photoshop and usually when everything is viewed digitally compression and quality doesn't matter as much compared to printing. When I export the image as a jpeg even at maximum quality selected the image file size will go down to 3mb the original tif file is 56.9mb, so that does seem like a significant reduction in quality.

 

I have attached the base tif file here, if anyone could provide some guidance that would be great. 

 

Best,

SHO 2.tif 56.91 MB · 7 downloads

White wall are good. You will need to set your black point high though. To about 35 or so, their metal sublimation prints are great. Across the board it's very hard to see detail in the blacks unless you illuminate the print heavily and that leaves the image looking washed out in the mid tones. Better to raise them and aim for something that looks good under natural light levels. I have found that images that look good printed do not look good on the monitor and vice versa. 

I print at 200 - 250 DPI. Depending on the subject imaged. 

Edited by Adam J
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On 02/10/2020 at 16:36, vlaiv said:

Would 100dpi be sufficient? Well, yes if you have something that can be only viewed at 873.19mm distance or 87cm away, but bear in mind - people want to get close to these sort of images to better see the detail.

Your best bet is to aim for reading distance - around 30cm and go for at least 300dpi.

I really don't think that's the case.

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24 minutes ago, Stub Mandrel said:

I really don't think that's the case.

Quite, if you can see the pixels then the detail is lost, because each pixel and its surrounding pixels will only be your post processing, your detail comes about around 50 pixels square, looked closely.

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1 hour ago, Stub Mandrel said:

I really don't think that's the case.

Not sure that I get what you mean by this?

That 100dpi corresponds to about 87cm viewing distance or that one needs 300dpi for reading distance and for this reason it is best to print in 300dpi as people tend to look at objects at "reading" distance when they want to inspect it in more detail?

 

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The acceptable DPI for any picture depends on what the picture is consisted of, if it is a sparse picture then people are going to look at detail (searching for it), if it contains a single point of interest then people will step back and (hopefully) admire the whole.

It's even better if it looks good as a whole, and yet when you move in you see further detail without loss of quality.

Edited by gilesco
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