Legacy ImageMagick Discussions Archive

experts:
I've been learning IM for a while, its amazingly powerful.
I'm reading a lot, but so far I couldn't find a good way to do what I wanted ...

the issue:

I have scanned a lot of picutures/photos (totally around 800), the complexities here are :

* when I scan them, I set different DPIs , sometime 200
* sometime I scan with input size A3 (for large pictures) , or A4
* I also have some other pictures that was taken by camrols.

my goals:
I want to re-format ALL of my pictures, and
* make sure they can be printed to exactly (or at least roughly) the same physical size (A4),
* while at the same time, for bigger images only, don't lose resolutions
* for smaller image, I don't mind if they are expanded and lose some resolutions [/b]

so the whole purpose is, this way, later on I can merge them into a a pdf book with each page has the same size, and to make hardcopies.

I know it's easy for IM to convert between different format, resize, sample, and so on...
but whenever I *resize* a large picture to smaller size, it looks not as clear as the orignal ones, I guess I lost the resolutoin here.
I'm wondering maybe I need to use some kind of *density* knobs, but no idea how to achieve this goal....


hope I can get some experts' advices...

thanks!

regards
ping

First you have to understand that pixel dimensions don't equate to printed size. The latter depends upon the pixel dimensions and the density.

So to keep the printed size the same you need to make sure that when you combine the pixel dimension with the density (resolution in inches or centimeters) so that it matches the physical printed size of the A4.

According to http://www.imagemagick.org/script/comma ... s.php#page, A4 has a pixel dimension of 595x842 presumably at 72 dpi.

Thus if you divide pixels dimensions x 72dpi you get 8.26 inches by 11.69 inches. That seems to closely match https://en.wikipedia.org/wiki/Paper_size which say 8.27 × 11.69

So what you want to do is find the image size (without resizing) and compute what density you need to achieve these printed sizes in inches. Then just set the density of the images.

convert image -density XX -units pixelsperinch result

To keep aspect ratio, you should not have -density XXxYY with different XX and YY. So you may need to either crop or pad your image appropriately.

If you want smaller pixel dimensions than in your original image, you can resize and then do the same computations, but if you get too small pixel dimension, then you will lose quality and image will look blocky.

Alternately, you can resize your images (cropping or padding) so that you can use a nominal density (say 150 or 300) for printing. So you have to work it the other way -- for the given density figure out what the pixel dimensions will need to be to achieve the given 8.26 inches by 11.69 inches

Now I am not an expert on printing. So perhaps some of the photography experts, who do printing, can add to or correct my comments.

What format are your images now? Was the density already saved to the files by the scanner?

ping wrote: whenever I *resize* a large picture to smaller size, it looks not as clear as the original ones, I guess I lost the resolution here

Correct, better to change the density as described by fmw42.

ping wrote: later on I can merge them into a pdf book

I don't know if IM can create a pdf with more than one image per page, especially if they are at different densities. I'm not sure about outputting a multi-page pdf either. Other tools will give you more control over outputting a pdf book. Is creating a pdf file your main goal, or are you also needing some other image processing?

I don't print via PDF files, because that just adds an extra layer of complexity. A4 paper is 297x210mm (11.693x8.238 inches), but most printers can't print up to all four edges. If you use ImageMagick to convert a load of images to a single PDF file, the pages will be different sizes and aspect ratios. You would need to normalise each image to the same dimensions first, and to do that you need to know the printer's DPI (eg 1200, 600 or whatever). And you should leave a margin on all four sides.

For creating a photo album such as you describe, Ghostscript might be a better tool than ImageMagick.

I don't normally resize an image (in pixels) before printing it; I leave that to the printer driver. If I (very rarely) want to specify the dimensions of an image (in inches), I do as fmw42 says ... ... where I have calculated XX as appropriate.

Note that PNG does not properly support units of pixels per inch. IM will convert any value specified as such into the equivalent pixels per centimeter.

thanks a million guys for pointing these out!
fmw42, I'll try what you say, see if I can put that calculation in a small cript...

based on these, I have a couple of more concerns:
1) [fmw42], first of all, when I scan these pictures, the scanner generate PDF format, I assume your method applys to PDF also ?right?

2) [GreenKoopa], I setup the scanner's DPI to 200 full color or sometime even 300DPI,

but strangely, they all looks with a DPI 72 now regardless of what I set up in scanner...

ping@640g-laptop:~/personal-materials/xinuosong/xixibook/xixibook-raw$ identify xixibook17.PDF
xixibook17.PDF[0] PDF 841x1189 841x1189+0+0 16-bit Bilevel DirectClass 126KB 0.030u 0:00.019
xixibook17.PDF[1] PDF 841x1189 841x1189+0+0 16-bit Bilevel DirectClass 126KB 0.020u 0:00.019
xixibook17.PDF[2] PDF 611x791 611x791+0+0 16-bit Bilevel DirectClass 126KB 0.020u 0:00.019
......
xixibook17.PDF[19] PDF 611x791 611x791+0+0 16-bit Bilevel DirectClass 126KB 0.010u 0:00.000
xixibook17.PDF[20] PDF 841x1189 841x1189+0+0 16-bit Bilevel DirectClass 126KB 0.010u 0:00.000
......
xixibook17.PDF[22] PDF 841x1189 841x1189+0+0 16-bit Bilevel DirectClass 126KB 0.000u 0:00.000
xixibook17.PDF[23] PDF 594x841 594x841+0+0 16-bit Bilevel DirectClass 126KB 0.000u 0:00.000
xixibook17.PDF[24] PDF 594x841 594x841+0+0 16-bit Bilevel DirectClass 126KB 0.000u 0:00.000


ping@640g-laptop:~/personal-materials/xinuosong/xixibook/xixibook-raw$ identify -format "%x x %y" xixibook17.PDF
72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 Undefined x 72 Undefined72 ......

but according to this post: forums.adobe.com/thread/285624
PDF "doesn't have a DPI", so I think the result of "identify" might be bogus?

if PDF is not supported, then what format shall I convert all my PDFs to , in order to proceed?

1) [fmw42], first of all, when I scan these pictures, the scanner generate PDF format, I assume your method applys to PDF also ?right?

Scanning to a pdf is not advised if you want to do any post processing. You should be able to select other formats besides pdf. Typically there should be jpg and/or tif.

The pdf will probably say 72 dpi, because that is the vector wrapper. You would need to use some other tool to extract the image from the vector wrapper. That is also why it is not advised to scan to pdf.

see
http://www.imagemagick.org/Usage/formats/#vector

If you must save a result as PDF, then it should be the last step.

I don't use IM and PDFs together, but here is some general info:

ping wrote:according to this post: ... PDF "doesn't have a DPI"

PDF is a vector format. PDF files may contain text, drawings, etc. that don't have DPI. PDF files may also contain raster images, each having its own DPI. A PDF from a scanner likely contains a single image at whatever DPI you set at the time of scan.

ping wrote:but strangely, they all looks with a DPI 72 now regardless of what I set up in scanner

When PDF files are read in by a raster image program such as IM, you generally must specify a DPI to convert the entire file. 72 DPI is probably IM's default, which you should set before the file is read in (probably using -density). PDFs may also be multi-page, so you may also specify a page range to read in.

fmw42 wrote:Scanning to a pdf is not advised if you want to do any post processing.

I only scan to PDF if I need OCR or am sending the file unmodified to someone who needs to print it. What you want is the single image saved in the PDF in whatever resolution it already is, and I don't know how to achieve that using IM. There are utilities that can extract the images from a PDF without loss of quality.

again thanks for the valueable infomations, I took a day to read/learn/test what you guys mentioned
so it all looks, my current issues are that my files are all in the PDF format, not easy for IM to process

so my issues are:

1. is it really that impossible (although hard) to achieve my goal based on PDF file, using IM?
2. shall I convert my PDF to what other format to proceed ? if yes, how about IM's convert command?

## for 1 , I did some testing:

according to [this link](http://www.imagemagick.org/Usage/formats/#vector) you pointed:

> Consequently if you are trying to convert a image from a vector format, to another vector format, IM will essentially rasterize this image at the currently defined resolution or density which will hopefully (but unlikely) be suitable for the output device you intend to use it on.

so I did a test:

for [this file](http://pinggit.github.io/images/xixiboo ... tate90.pdf)

$ identify a2-IMG_1626-1024x768-rotate90.pdf
a2-IMG_1626-1024x768-rotate90.pdf PDF 768x1024 768x1024+0+0 16-bit Bilevel DirectClass 98.4KB 0.000u 0:00.000

I use this command:

convert a2-IMG_1626-1024x768-rotate90.pdf -density 93x88 a2-IMG_1626-1024x768-rotate90-density.pdf

and I got [this new pdf](http://pinggit.github.io/images/xixiboo ... tate90.pdf)

$ identify a2-IMG_1626-1024x768-rotate90-density.pdf
a2-IMG_1626-1024x768-rotate90-density.pdf PDF 595x838 595x838+0+0 16-bit Bilevel DirectClass 62.9KB 0.010u 0:00.010

the `-density` value (93x88) are calculated based on the theory I learned from fmw42, so it's (1024/11.69 x 768/8.27)

I look at it, and print them to 2 A4 paper, for me basically, it looks the new file achieved what I hoped:
the size was shrunk to fit in an A4 paper for printing, but still looks as clear as the original one (not sure if it's more clearer)

these are good, but the only thing bad is, the new file is much *bigger (7 times in Bytes!)* than the original old one:

2330996 May 20 20:35 a2-IMG_1626-1024x768-rotate90-density.pdf <-- new file
335121 May 9 16:27 a2-IMG_1626-1024x768-rotate90.pdf

I'm guessing this was due to the internal tricks that IM is currently using , to convert between PDF (vector) images?

another thing I noticed, is that the DPI value we got from `identify` command seems to be 72DPI forever, even for the new file, which should be with DPI of 93x88, so it *IS* a bogus value, although my pdf image just contains one single picture in it.

but then even the pixel dimension it displayed (768x1024) is also bogus?

## for 2, I also did some test
I tested with 2 methods:

1. convert to *jpg* with IM's convert command
2. convert via [pdfimage tool](http://poppler.freedesktop.org/)

### first test: real picture
I first tried to convert [the same pdf photo](http://pinggit.github.io/images/xixiboo ... tate90.pdf) as above

$ pdfimages -j a2-IMG_1626-1024x768-rotate90.pdf test
$ convert a2-IMG_1626-1024x768-rotate90.pdf test2.jpg

$ identify test-000.jpg
test-000.jpg JPEG 768x1024 768x1024+0+0 8-bit DirectClass 327KB 0.000u 0:00.000

$ identify test2.jpg
test2.jpg JPEG 768x1024 768x1024+0+0 8-bit DirectClass 227KB 0.000u 0:00.000

$ identify -format "%x x %y" test-000.jpg
72 PixelsPerInch x 72 PixelsPerInch

$ identify -format "%x x %y" test2.jpg
72 PixelsPerInch x 72 PixelsPerInch

the generated files are here:
[via pdfimage](http://pinggit.github.io/images/xixiboo ... st-000.jpg)
[via convert](http://pinggit.github.io/images/xixibook-test/test2.jpg)

as I can tell:

* there are no difference, in terms of pixel size and resolution
* both picture looks as clear as the origial one
* just the IM version is 1/3 smaller than pdfimage version

### second test, drawings

I then did another test, this time the PDF under my test is not a real picture, but some drawings:
[oringal file](http://pinggit.github.io/images/xixiboo ... g_0113.pdf)

again I convert them into jpg via both tools.

interestingly, this time pdfimage generate a lot of files, while IM's convert only generate one file.

$ identify c-pg_0113.pdf
**** Warning: considering '0000000000 XXXXX n' as a free entry.

**** This file had errors that were repaired or ignored.
**** The file was produced by:
**** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<<
**** Please notify the author of the software that produced this
**** file that it does not conform to Adobe's published PDF
**** specification.

c-pg_0113.pdf PDF 612x792 612x792+0+0 16-bit Bilevel DirectClass 61KB 0.000u 0:00.000

$ pdfimages -j c-pg_0113.pdf c-pg_0113-pdfimage
Error (425): Command token too long

$ convert c-pg_0113.pdf -density 74x68 c-pg_0113-density74x68.jpg
**** Warning: considering '0000000000 XXXXX n' as a free entry.

**** This file had errors that were repaired or ignored.
**** The file was produced by:
**** >>>> itext-paulo-155 (itextpdf.sf.net-lowagie.com) <<<<
**** Please notify the author of the software that produced this
**** file that it does not conform to Adobe's published PDF
**** specification.

$ identify c-pg_0113-density74x68.jpg
c-pg_0113.jpg JPEG 612x792 612x792+0+0 8-bit DirectClass 104KB 0.000u 0:00.000

$ identify -format "%x x %y" c-pg_0113-density74x68.jpg
74 PixelsPerInch x 68 PixelsPerInch

generated files:

$ ls -l
total 12704
131928 May 21 17:32 c-pg_0113-pdfimage-000.jpg
6323873 May 21 17:20 c-pg_0113-pdfimage-000.ppm
1053989 May 21 17:32 c-pg_0113-pdfimage-001.pbm
1053989 May 21 17:32 c-pg_0113-pdfimage-002.pbm
1053989 May 21 17:32 c-pg_0113-pdfimage-003.pbm
1053989 May 21 17:32 c-pg_0113-pdfimage-004.pbm
37708 May 21 17:32 c-pg_0113-pdfimage-005.pbm
1053989 May 21 17:32 c-pg_0113-pdfimage-006.pbm
159420 May 21 17:32 c-pg_0113-pdfimage-007.pbm
1053989 May 21 17:32 c-pg_0113-pdfimage-008.pbm
103740 May 21 20:09 c-pg_0113-density74x68.jpg

they can be accessed in here:

[original](http://pinggit.github.io/images/xixiboo ... g_0113.pdf)
[pdfimage converted]
http://pinggit.github.io/images/xixiboo ... ge-000.jpg
http://pinggit.github.io/images/xixiboo ... ge-001.jpg
http://pinggit.github.io/images/xixiboo ... ge-002.jpg
http://pinggit.github.io/images/xixiboo ... ge-003.jpg
http://pinggit.github.io/images/xixiboo ... ge-004.jpg
http://pinggit.github.io/images/xixiboo ... ge-005.jpg
http://pinggit.github.io/images/xixiboo ... ge-006.jpg
http://pinggit.github.io/images/xixiboo ... ge-007.jpg
http://pinggit.github.io/images/xixiboo ... ge-008.jpg
[IM's convert]
http://pinggit.github.io/images/xixiboo ... y74x68.jpg

the interesting thing is, if you look at the jpg file that `pdfimage` extracted
from the original pdf, some parts of the drawing are missing... and they are put
in other `ppm` files.

My guess, based on the reading, is that the original drawing, when be scanned by
the printer, my printer happened to recognized some part of the drawing and
match them into some kinds of vector objects and hence stored in a different
format as a seperated objects, in the same PDF picture. that's why `pdfimage`
extract them into different files?

1. is it really that impossible (although hard) to achieve my goal based on PDF file, using IM?
2. shall I convert my PDF to what other format to proceed ? if yes, how about IM's convert command?

1. Probably. You would be better to scan to JPG or Tiff

2. You can extract the image first, but not via IM. See http://www.imagemagick.org/Usage/formats/#ps for other tools that will extract the image from the pdf

Once you have the image from the PDF, you should be able to proceed as described earlier.

Before we get lost in the details, lets go back to your constraints and goals.

1. You are starting with scanned-in PDFs. For images this possibly wasn't the best or easiest choice, but not necessarily catastrophic if you already have hundreds of scans. IM or otherwise, you probably need to extract the images before you can do anything with most any tool.
2. Is a PDF book the firm goal? Or are you just trying to resize (set DPI) and print?
3. You haven't mentioned any need for image processing or for scripting, so why IM? Why not extract the images from the scanned PDFs, import them into OpenOffice or whatever, resize the images and layout your pages, and save as a PDF?

hi GreenKoopa:
thanks for the summarization, I think you hit the essential of my issues here.


1. You are starting with scanned-in PDFs. For images this possibly wasn't the
best or easiest choice, but not necessarily catastrophic if you already have
hundreds of scans. IM or otherwise, you probably need to extract the images
before you can do anything with most any tool.

[ping]: I'm now learning what's the best tools to achieve that, some above links pointed to:

>Solutions include

> "pstoedit" to convert to other vector formats such as SVG.
> "pdftoppm" from the "ghostscript" package.
> "pdfimage" from the "xpdf" package.

>Another posibility presented by Wolfgang Hugemann is to directly extract any
>image contained by a PDF (especially from PDF's generated by scanners).
>Basically by extracting any byte sequence between "stream" and "endstream",
>and saving as a separate file.

I'm testing them one by one and see how to use them well...

2. Is a PDF book the firm goal? Or are you just trying to resize (set DPI) and
print?

[ping]: the PDF book is not the firm goal, but just a side product. I just want
to produce something (preferably PDF, but can be anything), that I can then
later send to the printing agent, so they can generate a decent-looking hardcopy
(with all images fit in A4 size nicely) for me.

3. You haven't mentioned any need for image processing or for scripting, so why
IM? Why not extract the images from the scanned PDFs, import them into
OpenOffice or whatever, resize the images and layout your pages, and save as
a PDF?

[ping]: I'm not mean to script, but only goal is to have a consistent looking
hardcopy book as I mentioned about. the method you mentioned here is also a good
hint. initially I thought since I have around 800 drawings (including a few
photos), I was thinking get nice CLI tools (like IM) is good for scripting...

so it all looks I now need to quick/tested way to extract PDF to images, do you
know of any verified easy way to do that? Otherwise I'm still spending days to
study those CLI tools (IM,pstoedit,...), while my deadline of the book delivery
are approaching ...

and, what image format is the best for me to convert to?

thanks as always!

search google for "extract image from pdf". there are lots of solutions and they may depend upon your platform, window, linux or mac. Not sure what you are using.

Your wanting a PDF book and A4 paper makes me think you are sending this to a document print shop (Kinkos around here), not a photo shop which would want jpegs. Perhaps we are over thinking your need. You can place images into book.pdf like this. See if it works for you too. Then replace the sample images with a few of your pdf scans.

convert -density 200 rose: logo: wizard: hald:4 -rotate "-90>" -resize 1500x2185 -page 1653x2338+27+27 book.pdf