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07-28-2022, 06:15 PM   #1
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Increasing image size

I have owned the K20D for quite some time and happy with its performance. Now I want to make some large prints 20x30 inches from some of the images I captured with it.My printer wants me to send him jpegs with 300 DPI resolution. However, the pef images captured by the K20D has 72 DPI resolution with an image size of 3136 x 4864 Pixels with print size of 43.11 x 64.89 inches. If I change the resolution to 300 DPI, I get an print size of 10.35 x 15.57 inches. How do I bump up the print size to 20 x 30 inches? I use RawTherapee as the raw image processor and Gimp as my photo editing software, though admittedly I am not conversant with all the features of Gimp.

I was told that increasing the print size invariably reduces the image quality. How can this degradation be minimized?

mj

07-28-2022, 06:33 PM - 1 Like   #2
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Enlargement software like gigapixel can greatly help with this (Topaz Gigapixel AI Review - Introduction | PentaxForums.com Reviews).

The conventional way is just to up sample the image and apply some sharpening, which would be less detailed of course, but might work depending on the viewing distance for the print.

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07-28-2022, 06:49 PM   #3
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I recommend Gigapixel, I think there is a trial version, but PF also has a discount code. IT's money well spent, from my personal experience. IF you have a good source image, Gigapixel will enlarge it up to 4x with very good results.
07-28-2022, 07:01 PM   #4
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The other answer: increase pixels. Either by upgrading the sensor (The k-1 gives 36m) or stitching multiple images to increase pixels.

07-28-2022, 07:27 PM - 1 Like   #5
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There's new software called On1 Resize AI that's getting excellent reviews.
I've tried it with old images from my K200D and got great results.
07-28-2022, 11:30 PM - 1 Like   #6
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QuoteOriginally posted by mmjoshi Quote
I have owned the K20D for quite some time and happy with its performance. Now I want to make some large prints 20x30 inches from some of the images I captured with it.My printer wants me to send him jpegs with 300 DPI resolution. However, the pef images captured by the K20D has 72 DPI resolution with an image size of 3136 x 4864 Pixels with print size of 43.11 x 64.89 inches. If I change the resolution to 300 DPI, I get an print size of 10.35 x 15.57 inches. How do I bump up the print size to 20 x 30 inches? I use RawTherapee as the raw image processor and Gimp as my photo editing software, though admittedly I am not conversant with all the features of Gimp.

I was told that increasing the print size invariably reduces the image quality. How can this degradation be minimized?

mj
Very roughly calculated, you're aiming for 300dpi but you'll have about 157dpi using an image straight from the camera. As others have noted, you'd either have to use an upscaling program or you'd need to shoot a group of images, stitch those in post to create one image.

Be that as it may, another thing to be considered is viewing distance: With other words, if you look at your 30x20" print from up close, it will be obvious that it's a 157dpi image, if printed without any AI work done to it, but if your image is likely to be viewed from some distance, then the resolution becomes less important.

You may want to print a sample image(of a part of the image) and see if the quality matters at the viewing distance you envision. Good luck!
07-29-2022, 12:21 AM - 5 Likes   #7
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Using the software that you've got available, my preferred option would be the Lanczos upsampling in RawTherapee. Save the photo that you want to print as an uncompressed tiff file, then open the tiff in RawTherapee -- don't worry, it's capable of working with tiff and jpeg as well as raw. Turn off all processing options except resizing, choose Lanczos upsampling, and set the pixel dimensions to 6000x9000 (20"x30" at 300dpi). Then save the upsampled photo as a new tiff (or jpeg if that's what your printer demands).

Lanczos scaling is the best quality you'll get without investing in AI upsampling software like Topaz Gigapixel, and at normal viewing distances the quality will be fine. The sort of people who like to examine prints from three inches away might feel that it's not up to their standards, but honestly who cares what people like that think.

At the risk of going off topic, a thing that will make a much bigger difference to how the print looks at normal viewing distances is soft proofing. You'll find plenty of helpful guides online showing you how to do that in GIMP after you've resampled to the right size.

07-29-2022, 01:38 AM   #8
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You will get better results if you just increase the photo size by 10% each time repeatedly until you get to the desired size, rather than jumping up to full size in one hit.
07-29-2022, 04:14 AM   #9
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QuoteOriginally posted by DeKay Quote
You will get better results if you just increase the photo size by 10% each time repeatedly until you get to the desired size, rather than jumping up to full size in one hit.
Do you have any examples or articles showing this? What program or method is used to do the expansions?
07-29-2022, 05:15 AM   #10
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QuoteOriginally posted by DeKay Quote
You will get better results if you just increase the photo size by 10% each time repeatedly until you get to the desired size, rather than jumping up to full size in one hit.
That's interesting. I've never tried any of the enlarging software but have watched a couple videos on them and have never seen anyone do it that way, it would be interesting to see the result difference.
07-29-2022, 06:33 AM - 1 Like   #11
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QuoteOriginally posted by MarkJerling Quote
Very roughly calculated, you're aiming for 300dpi but you'll have about 157dpi using an image straight from the camera. As others have noted, you'd either have to use an upscaling program or you'd need to shoot a group of images, stitch those in post to create one image.

Be that as it may, another thing to be considered is viewing distance: With other words, if you look at your 30x20" print from up close, it will be obvious that it's a 157dpi image, if printed without any AI work done to it, but if your image is likely to be viewed from some distance, then the resolution becomes less important.

You may want to print a sample image(of a part of the image) and see if the quality matters at the viewing distance you envision. Good luck!
Just as examples, I typically export my RIP files at 100ppi which is more than needed for a large print being viewed three feet away. You won't see the pixels. For really large stuff, maybe 5 feet tall and 10 feet wide, 50ppi is plenty. When we used to print billboards those were at 15dpi and looked great.

As you are recommend Mark, folks should print a sample at a lower resolution to see if a reduced size is just as effective at the intended viewing distance before spending excessive effort on creating a 300-600ppi or higher file. It's resources wasted if you can't tell the difference.
07-29-2022, 06:58 AM   #12
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QuoteOriginally posted by gatorguy Quote
Just as examples, I typically export my RIP files at 100ppi which is more than needed for a large print being viewed three feet away. You won't see the pixels. For really large stuff, maybe 5 feet tall and 10 feet wide, 50ppi is plenty. When we used to print billboards those were at 15dpi and looked great.



As you are recommend Mark, folks should print a sample at a lower resolution to see if a reduced size is just as effective at the intended viewing distance before spending excessive effort on creating a 300-600ppi or higher file. It's resources wasted if you can't tell the difference.
Even if you can't tell the difference some printers ask for 300dpi images.

07-29-2022, 07:13 AM   #13
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QuoteOriginally posted by DeKay Quote
You will get better results if you just increase the photo size by 10% each time repeatedly until you get to the desired size, rather than jumping up to full size in one hit.

I'm not sure how that could work. You'd be interpolating samples, then interpolating again and again and again, each time using worse data because of the previous interpolations.
07-29-2022, 08:00 AM   #14
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Given you selection of tools (GIMP + RawTherapee) I would suggest using the GIMP resynthizer plug-in as an option as it does have a resize option. Another GIMP plug-in to consider is the GIMP-ML plug-in. Both of these do some form or synthesis instead the nearest neighbor, or interpolation of linear, cubic, or lanczos scaling techniques. When the new pixels are made up instead of smoothed it shouldn't result in a perceived degradation in image quality like what one sees with interpolation methods.
07-29-2022, 08:03 AM   #15
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QuoteOriginally posted by KiloHotelphoto Quote
That's interesting. I've never tried any of the enlarging software but have watched a couple videos on them and have never seen anyone do it that way, it would be interesting to see the result difference.
It was all the rage years ago, as was stuff like 'just go 200% and let the printer driver/RIP do the rest.' It can work well. It can also not be the best method.


Image subject and capture (quality) matters, as does the PP work from WB to output sharpening, the two printers(person/machine), the substrate, etc. It can be worth the effort to make several test sample files, say 8x10ish depending on the two printers capabilities. This allows one to see the differences between screen and print output and say a file upped to 300dpi at your end vs one where the printer is given the duty; some of which are quite capable (not all Canon printers run the same software). The printer (person) ideally wants to do as little as possible to your file beyond inputting the number of copies and selecting the media; we do not know their capabilities - there can be a world of difference between a fella with a home office and prograf-2000 trying to defray the COO versus the the folks at a service/print shop with a set of prograf-6100's, or they can give you for all intents, the same output.
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