I'm trying to have an identical output to what Adobe Acrobat does with File>>Save As>>Image>>JPEG. But whenever I use ImageMagick's convert it takes much longer and the resulting file is 2-3x bigger. I set the density option to -density 686 because that was the density of Acrobat's output according to the following:
Here is the result of convert (filename changed to Bitter_Creek.jpg), not sure why it says aspect ratio and the dimensions will still differ even when setting the size option to -size 14859x18388
Using the ls -l command to describe the resulting JPGs I get this:
(top file is result of ImageMagick's convert and the bottom file is result of Acrobat's Save As:
I would like to know which options to use to get an identical output.
Filesize of a jpeg image depends on quality setting. The default setting of Acrobat is "Medium" whose quality value is considerably low (62), whereas ImageMagick's convert is defaulted to higher value.
If you expect the equivalent result, add -quality 62 option to convert, although picture quality will be accordingly degraded.
Related
I am using ghostscript 9.25 windows.
I am trying to convert RGB pdf to CMYK preserve pdf using following command:
gswin32c.exe
-dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite -sColorConversionStrategy=CMYK -dProcessColorModel=/DeviceCMYK -dAutoFilterColorImages=false -dAutoFilterGrayImages=false -sOutputFile=out.pdf input.pdf
input.pdf file here
https://www.dropbox.com/s/8jfnov526nhb9m9/blank.pdf?dl=0
output.pdf file here
https://www.dropbox.com/s/ftrmm32mmixaxqh/out.pdf?dl=0
but my output becomes light compared adobe output, expected result is it should be dark when i do in adobe CMYK preserve option, i am getting little dark compared to ghostscript output. Am I doing anything wrong?
Should I use any icc profile?
Thanks
You say you are using ImageMagick, yet you give a Ghostscript command line....
I presume that when you say CMYL you mean CMYK.
There is nothing immediately obviously wrong with your command line, but you have given no example file, nor any reason why you expect the result to be 'dark'.
If you want to control the conversion then you will need to supply at least one and possibly up to 4 ICC profiles. You will certainly need a CIE->CMYK Output profile, and you might like to supply ICC profiles for Gray->CIE, RGB->CIE and CMYK->CIE as well, in order to override the default ones Ghostscript is using.
[EDIT]
The problem is nothing to do with colour conversion. Your original file contains nothing except a very large image, which is compressed with the Flate filter (lossless). It looks like this:
You've turned off auto filtering, but you haven't told Ghostscript which compression filter to use for images, so it sticks with the default, which is JPEG (DCT). The image now looks like this:
For the nature of your original image, JPEG (lossy) compression is an outstandingly bad choice. The output image compresses less well, and it loses fidelity. You should change to using Flate compression instead of JPEG for images of this kind.
By the way, the image in your original PDF file was defined in CMYK space already.
I have a directory called "plots_for_gifs", which contains 105 files, whose names are identical apart from they end in ...000.png, ...001.png ... etc. up to ...104.png. I am trying to convert them to a .gif using:
convert -density 150 -trim -delay 35 -loop 0 ./plots_for_gifs/*.png ./river_diff.gif
The image files are 491x411 pixels, however the gif produced is 7017x4958 pixels! Even though I am including "-trim", and the same occurs even if I add "-size 491x411"... any ideas?
I am running this in a bash shell in Ubuntu 16.04.3.
Mmmmm.... a couple of things.
You don't need -density at all with PNG files because it only sets the density to be used when rasterising vector files such as SVG. So, you can omit that.
If, as you say, your images are already the correct size, you don't need -trim. So, you can omit that too.
You don't need to prefix filenames with ./, as that just means "the current directory" which is the default anyway, so you can omit that.
Now to the actual problem. I guess your PNG files have been cropped from some larger images and have "remembered" their previous canvas size. The best way to make them forget, is to use +repage after loading them.
So, without seeing your files, I suspect you want something more like:
convert -delay 35 -loop 0 plots_for_gifs/*.png +repage river_diff.gif
If you find you do need -trim, add it into the above command before +repage.
If that doesn't work, please run the following command and paste the output in your original question - by clicking edit underneath it:
identify plots_for_gifs/*000.png
I use gostscript to convert text to outlines with the following code :gswin32c.exe -sDEVICE=pdfwrite -sOutputFile=output.pdf -dQUIET -dNOPAUSE -dBATCH -dNoOutputFonts -f test_new.pdf,it works.But i got a very small output file from 2.5M to 70kb.Then i find the picture became blurred in pdf.
Add -dPDFSETTINGS=/default,This will have the same result.
I's better to use -dPDFSETTINGS=/printer or -dPDFSETTINGS=/prepress,but 300dpi is not enough for me(or for my boss).
Is there any way to keep the original resolution of the picture.
Or how to set a higher dpi for images in output pdf.
The test file is here.
Thanks in advance.
The answer to your question is 'yes' (but see later). Don't use PDFSETTINGS, that sets lots of things all in one go. If you want control then you need to specify each setting individually.
Rather than use this shotgun approach you need to read the documentation, decide which controls affect areas you want to change, and alter those controls only.
However, image downsampling is not your problem. If you don't use -dPDFSETTINGS then PDF file written by Ghostscript contains an image at exactly the same resolution as the image in the original file.
Your problem is that the image is being written with JPEG compression, and JPEG is a lossy compression, so you are losing fidelity. Note that in the original file the image is written uncompressed, which is why its so large.
It looks like the original image was a JPEG, and the free PDF editor you are using has realised that so it saved the image uncompressed (I may be giving it too much credit here, it may save all images uncompressed). Applying JPEG to an image which has already been quantised simply amplifies the artefacts.
Instead you need to specify that you want images compressed with Flate, which is a lossless compression. The documentation for the pdfwrite controls can be found here, you need to change AutoFilterColorImages and ColorImageFilter.
Note that by not applying JPEG quantisation (a second time) and DCT encoding, the compression is less than your first experience. For me the output file comes in at just over 600Kb (leaving the font in place, and the text as text, would be a couple of Kb smaller). However the image is identical, as expected.
Since you are clearly using Ghostscript in a commercial environment, can I just point you at the licence and ask you to check that your usage is compatible with the AGPL, bearing in mind that this covers software as a service usage as well.
I am using GhostScript to convert large batches of PDF to PDF to reduce file size. The original PDFs vary in size and quality. Where there is a low quality, small file size (<350kb) PDF the output from Ghostscript is often poor.
Is there a way I can get GhostScript to ignore files below a certain size and just pass them through without downsampling?
Current settings:
SearchablePDFSetting=-dColorImageResolution=120 -dMonoImageResolution=38 -dMonoImageDownsampleType=/Average -dOptimize=true -dDownsampleColorImages=true -dDownsampleGrayImages=true -dDownsampleMonoImages=true -dUseCIEColor -dColorConversionStrategy=/sRGB -dFIXEDMEDIA -dDEVICEWIDTHPOINTS=596 -dDEVICEHEIGHTPOINTS=834
Thanks,
Vix
The pdfwrite device can already pass images (not files) through without downsampling, there is no way to 'pass through without changing' a file. If you want to not process files below a certain size, then don't process them.
To avoid further downsampling of images, you need to add the 'xxxxImageDownsampleThreshold' parameters (one each for Mono, Grey and Color). If you set this to (eg) 1.5 then images which are up to 50% higher resolution than the target resolution won't be downsampled.
Note that you haven't (apparently) set a GrayImageDownsampleResolution, you haven't set the downsample type for Color or Gray images and a MonoImageResolution of 38 looks pretty ugly to me.
The default Gray image filter is DCT (JPEG) as is the Color filter. If the original image was DCT then applying a second round of DCT compression will result in ugly artefacts, especially if the image is not downsampled. I would suggest you change the filter type to FlateEncode.
All these options are documented in ps2pdf.htm in the Ghostscript doc folder.
Add the option:
-dPDFSETTINGS=/screen
This "selects low-resolution output similar to the Acrobat Distiller 'Screen Optimized' setting."
I would like to split a large PNG file into A4 pages so they can be printed out easily.
I would like to use a Linux command line script to do this:
shell> split-into-a4-sized-pages some-big.png
I assume you have ImageMagick & pdfposter installed.
A) convert your .png to .pdf (using ImageMagick)
convert input0.png input1.pdf
B) tile your image using pdfposter:
pdfposter -s4 input1.pdf out.pdf
this command enlarges input0 exactly 4 times, print on the default A4
media, and let pdfposter determine the number of pages required.
Try using imagemagick's crop to your desired size.
Say you have a 640x962 image:
and you want to crop it into 4 320x481 images:
Use:
convert pexels-adonyi-gábor-1400172.jpg -crop 240x240+0+0 cropped.jpg
convert pexels-adonyi-gábor-1400172.jpg -crop 320x481+320+0 cropped.jpg
convert pexels-adonyi-gábor-1400172.jpg -crop 320x481+0+481 cropped.jpg
convert pexels-adonyi-gábor-1400172.jpg -crop 320x481+320+481 cropped.jpg
Now you'd have to find out how many pixels fit into an A4 page in your printer, and the dimensions of the image, and it is a very simple script from here.
Photo by Adonyi Gábor from Pexels.
You can use convert of ImageMagick to scale the image; there are probably other tools in ImageMagick to clip the image if you want.
I don't know of any ready-made command line tool to do this. Unless you use it all the time, ImageMagick may take longer to figure out the right combination of commands and options, than to write a quickie program.
An easy way, if you know Python at all, is write a few-line program using PIL (Python Imaging Library). To read an image takes one line. To extract chunks of some width and height at specified location to save as new image files, is also easy. Add a couple for loops to scan rows and columns of A4-sized chunks, and you're done.
If you don't know Python, just about all quick-to-write programming languages have a similar capability. The GD library comes to mind; it has bindings for several languages.
NetPBM's pamdice will do the splitting into multiple pages. You'll have to set the -width and -height options according to the DPI of your desired A4 images.
And you'll also have to convert the input image to netpbm format first with pngtopam:
pngtopam big.png | pamdice -outstem tile -height h -width w
That will leave you will a bunch of files called tile_x_y.ppm
Convert each one of those to PNG with pnmtopng