Author Topic: Problem about the images quality  (Read 649 times)

Omino di Carta

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Problem about the images quality
« on: October 18, 2016, 01:43:00 pm »
Hi everybody,
I'm new of the forum. I've a problem about the images quality when I export in PDF for printing (CMYK). I use Scribus 1.4.5. I notice that the quality of the images are lower than the original versions, even if not too. I see this problem above all in the gradients: in a few words there is the banding effect, but the images are TIFF in high resolution (400 dpi). I export the PDF with a minimum resolution for the images of 400 dpi. I have tried to combine methods and qualities of compression, but the result is always the same, also without compression method. Is there anything that escape me?

Thanks and excuse my poor English.

a.l.e

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Re: Problem about the images quality
« Reply #1 on: October 18, 2016, 02:17:45 pm »
ciao omino di carta

welcome in the forum.

can you please provide:

- a sample .sla
- with a sample image
- and the pdf this produces?

anyway, if you want to have the images in the same resolution as in the .sla, you don't need to set a minimal or maximal image resolution. just get them to be embedded as is.

Nermander

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Re: Problem about the images quality
« Reply #2 on: October 18, 2016, 03:59:17 pm »
What are you using to view the PDF? I think it may be an issue with your PDF viewer, because Scribus will usually embed an image "as is" (unless you request downsampling of large images).

Omino di Carta

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Re: Problem about the images quality
« Reply #3 on: October 19, 2016, 12:09:19 am »
Thank you for your replies, a.l.e and Nermander.
I use Adobe Acrobat Reader DC to view the PDF, but I see the banding also if I put the file in the browser Chrome, for example. I think that the problem concerns the exporting process, not the viewer or Scribus. I tried to attach a original image and only the page of the book with it in PDF, but the files are too large, also in a zip archive (9,35 MB). Anyway, there is a very light banding also in the original file, probably it become more accentuated during the export.

Omino di Carta

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Re: Problem about the images quality
« Reply #4 on: October 19, 2016, 12:53:01 am »
Hi,
update of the situation: I tried to import the PDF in Photoshop and, magic, the image is like the original. Should I trust of Photoshop and not of Adobe Acrobat Reader? :o

mnawij

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Re: Problem about the images quality
« Reply #5 on: October 19, 2016, 01:40:23 am »
Hello Omino di Carta,

Is the banding only on the screen or also when you print on a postscript level 2/3 printer? Banding can occur as a display issue depending on your video card and the OS settings.  Also are you "rasterizing" the whole pdf in photoshop or are you using the import photo option to retrieve it out of the pdf?  You could place the same original picture by itself within Scribus and making the document size the same and then export to pdf with the same settings and see what happens... if the banding is there you can then upload the new pdf which should be smaller (in theory anyway). If the banding is not there maybe you have some elements over the photo such as vector or type? Another option is to save the tiff as a different file type such as png, eps, bmp, or jpg as a last resort and recreate the pdf to see if the banding is still there.

mnawij

a.l.e

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Re: Problem about the images quality
« Reply #6 on: October 19, 2016, 10:35:32 am »
framadrop is a good was for sharing files...

https://framadrop.org/

:-)

Omino di Carta

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Re: Problem about the images quality
« Reply #7 on: October 19, 2016, 12:22:29 pm »
Hello Mnawij,

the banding is on the screen. If it's a problem caused by the video card, I think that I should see the banding also in Photoshop. To see the PDF in Photoshop I simply opened the PDF page (with the TIFF image) that I exported from Scribus to try, without changing the resolution (400 dpi).
I tried, as you told me, to export the PDF page in another format (JPG). I imported it in Scribus and exported the PDF. In Acrobat Reader I have the same problem (perhaps worse). And, like before, there isn't  the problem in Photoshop. I tried to save the TIFF in JPG, import it in Scribus and export the PDF. The banding is a little less but it's present in Acrobat. Also in this test, in Photoshop there isn't the problem.
It's true that a light banding there is in the original file (I'm a illustrator and always I clash with the problem of large raster gradients, I can only reduce the banding with a little of noise effect), but I don't think that Photoshop adds and views something that there isn't. I don't think even that it fixes the banding. It will be Acrobat that visualizes badly instead. A little odd!
« Last Edit: October 19, 2016, 12:30:30 pm by Omino di Carta »

Omino di Carta

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Re: Problem about the images quality
« Reply #8 on: October 19, 2016, 12:47:51 pm »
Hello everybody,

this is the link of Framadrop (thank you a.l.e) for the zip archive with the original image (TIFF) and the PDF page with it: https://framadrop.org/r/n0YTH4KeY6#fMEqw7ffM2f0dgXf5E0vOorAwQeUqILpsjvKJuvHcBU=
The banding is on the background, more on the bottom.

Thanks
« Last Edit: October 19, 2016, 12:54:43 pm by Omino di Carta »

mnawij

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Re: Problem about the images quality
« Reply #9 on: October 20, 2016, 08:08:52 am »
Banding issues are always a pain, at least for me.  Transparency flattening can also cause banding, not sure how it works in Scribus, but I have the same problems with Indesign and Illustrator if I choose pdf 1.4 and lower.  Also have you tried changing the colorspace to RGB to see if it still happens? Just trying to narrow down the possibilities... Another issue with low color value gradients is if the photo is 8bit, I am not sure if 16bit images can be used in Scribus and it's pdf export though.  Also photoshop always has had banding issues that are not always noticeable, CS6 and above has a dithering option to help smooth these out but before that you had to use the blur or spatter type filters to improve gradients.  In photoshop open the hue/saturation, bump hue to 180 and the saturation to 70-90 and you will see the banding that is there increased dramatically.  Also which program did you do the original design work, a vector program or bitmap? Vector gradients converted to bitmap/raster seem to always have more problems when printed than printing straight from a vector program.  I will try and print it on my digital press sometime in the next few days and get back to you in the banding is seen when printed.  I hope I am not confusing you even more.

mnawij

a.l.e

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Re: Problem about the images quality
« Reply #10 on: October 20, 2016, 08:35:52 am »
the images shows ok here.

i've extracted it from the pdf and i get a 1379x2204 image that looks ok when magnified.

but it's not the same resolution as in the original image (half of it)

hard to say why, without being able to see the .sla file (and the pdf export settings)

ah, one last thing: i cannot recognize any "buffa ironia" in the image... the error must be much deeper...

Omino di Carta

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Re: Problem about the images quality
« Reply #11 on: October 20, 2016, 11:34:59 am »
Banding issues are always a pain, at least for me.  Transparency flattening can also cause banding, not sure how it works in Scribus, but I have the same problems with Indesign and Illustrator if I choose pdf 1.4 and lower.  Also have you tried changing the colorspace to RGB to see if it still happens? Just trying to narrow down the possibilities... Another issue with low color value gradients is if the photo is 8bit, I am not sure if 16bit images can be used in Scribus and it's pdf export though.  Also photoshop always has had banding issues that are not always noticeable, CS6 and above has a dithering option to help smooth these out but before that you had to use the blur or spatter type filters to improve gradients.  In photoshop open the hue/saturation, bump hue to 180 and the saturation to 70-90 and you will see the banding that is there increased dramatically.  Also which program did you do the original design work, a vector program or bitmap? Vector gradients converted to bitmap/raster seem to always have more problems when printed than printing straight from a vector program.  I will try and print it on my digital press sometime in the next few days and get back to you in the banding is seen when printed.  I hope I am not confusing you even more.

mnawij

Hello mnawij,
I tried to export the PDF in RGB and the situation is better. I know that in 16 bit the banding problem is lesser, but the files become more large. I use Photoshop to color my illustrations and , when it is needed, I add a little noise effect only on the level with the ugly gradient. When I created this illustration I was less careful than now and I tried to solve after, anyway, improving the gradient. In print I don't know if the banding will be visible, there is also the printer quality variable. Anyway, I thank you for your future print test, so we will see what is happen.


the images shows ok here.

i've extracted it from the pdf and i get a 1379x2204 image that looks ok when magnified.

but it's not the same resolution as in the original image (half of it)

hard to say why, without being able to see the .sla file (and the pdf export settings)

ah, one last thing: i cannot recognize any "buffa ironia" in the image... the error must be much deeper...


Hello ale,
the quality of image depends also from the monitor. I use an old cathodic tube monitor: the lcd ones don't go well for coloring, they are too bright (only the most expensive ones go well!). I don't know what type of montor you use, anyway, yes, it's true. Maybe it will visible in print. The resolution of the image in PDF is reduced second the exporting setting to 400 dpi (the original image is in 600 dpi). Since I have both images in 400 dpi and images in 600 dpi, I set to 400 dpi minimun. So I think the PDF size will be lighter.
Then, don't worry, the "buffa ironia" isn't a special thing! This bunny girl isn't  a real bunny, not? :D
« Last Edit: October 20, 2016, 11:36:48 am by Omino di Carta »

a.l.e

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Re: Problem about the images quality
« Reply #12 on: October 20, 2016, 11:57:03 am »
if you want to keep control of the way your image gets resized, you have to resize it in gimp before loading it into scribus!

if you check the image shrinking, while exporting to pdf from scribus, you have no control on the way the process ends.

... and yes, now i see how "buffa ironia" could be a thing: a bunny that is not a bunny is no irony, so you you mean that calling it irony is funny... or not.
(do yourself a favor: do not share such images on forums that are not about rabbits; they could be misunderstood)

Omino di Carta

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Re: Problem about the images quality
« Reply #13 on: October 20, 2016, 04:39:50 pm »
if you want to keep control of the way your image gets resized, you have to resize it in gimp before loading it into scribus!

if you check the image shrinking, while exporting to pdf from scribus, you have no control on the way the process ends.

... and yes, now i see how "buffa ironia" could be a thing: a bunny that is not a bunny is no irony, so you you mean that calling it irony is funny... or not.
(do yourself a favor: do not share such images on forums that are not about rabbits; they could be misunderstood)

You are right, but when I tried to export only the page with the image in 600 dpi (therefore without resizing by Scribus), I got the same result. I wait the possible print of mnawij, if printed it results well, it's only a visualization issue.

Regarding the illustration, its meaning would be clearer (I hope!) knowing the character, her personality and her story. This illustration isn't end in itself. It would be a teasing of her be a pin-up: the character is a model and, in this illustration, she mocks herself. Anyway, I will follow your advice!

mnawij

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Re: Problem about the images quality
« Reply #14 on: October 25, 2016, 03:39:49 am »
OK, I printed both the .tif and pdf file on my digital press.  The .tif file printed great very minimal banding.  The .pdf file the banding showed up mainly the bottom third of the gradient, though not as bad as what is viewed on the screen, but definitely still noticable.  The only difference I see between the two files is the .tiff is 600dpi whereas the .pdf file is 400dpi, so there is downsampling taking place somewhere in the pdf export and that could definitely be causing the banding.

Hope this helps,

mnawij