I have many scanned document in PDF.
I use ImageMagick with Ghostscript to convert PDF to PNG in big density. I use convert -density 288 2.pdf 2.png. After that I read the pixels with PHP and find where is QR code and decode it. Because image is very big (~ 2500px), it's need very much RAM. I want, before I read pixels with PHP, to crop the image with ImageMagick and leave only that part with the QR code.
Can I detect the approximate location of QR code with ImageMagick, crop and leave only that part ?
Sample PDF
Converted PNG
Further Update
I see your discussion with Kurt about better extraction of the image from the PDF in the first place, and his recommendation was to use pdfimages. I just wanted to add that you won't find that if you do brew search pdfimages, but you actually need to use
brew install poppler
and then you get the pdfimages executable.
Updated Answer
If you change the tile size to 100x100 on the crop command and run this for the second PDF you supplied:
convert -density 288 pdf2.pdf -crop 100x100 tile%04d.png
and then use the same entropy analysis command
convert -format "%[entropy]:%X%Y:%f\n" tile*.png info: | sort -n
...
...
0.84432:+600+3100:tile0750.png
0.846019:+600+2800:tile0678.png
0.980938:+700+400:tile0103.png
0.984906:+700+500:tile0127.png
0.988808:+600+400:tile0102.png
0.998365:+600+500:tile0126.png
The last 4 listed tiles are
Likewise for the other PDF file you supplied, you get
0.863498:+1900+500:tile0139.png
0.954581:+2000+500:tile0140.png
0.974077:+1900+600:tile0163.png
0.97671:+2000+600:tile0164.png
which means these tiles
I would think that should help you pretty much approximately locate the QR code.
Original Answer
This is not all that scientific, but it may help you get started. The key, I think, is the entropy of the various areas of the image. The QR code has a lot of information encoded in a small area so it should have high entropy. So, I use ImageMagick to split the image into square 400x400 tiles like this:
convert image.png -crop 400x400 tile%03d.png
which gives me 54 tiles. Then I calculate the entropy of each of the tiles and sort them by increasing entropy, also outputting their offsets from the top left of the frame, and their name, like this:
convert -format "%[entropy]:%X%Y:%f\n" tile*.png info: | sort -n
0.00408949:+1200+2800:tile045.png
0.00473755:+1600+2800:tile046.png
0.00944815:+800+2800:tile044.png
0.0142171:+1200+3200:tile051.png
0.0143607:+1600+3200:tile052.png
0.0341039:+400+2800:tile043.png
0.0349564:+800+3200:tile050.png
0.0359226:+800+0:tile002.png
0.0549334:+800+400:tile008.png
0.0556793:+400+3200:tile049.png
0.0589632:+400+0:tile001.png
0.0649078:+1200+0:tile003.png
0.10811:+1200+400:tile009.png
0.116287:+2000+3200:tile053.png
0.120092:+800+800:tile014.png
0.12454:+0+2800:tile042.png
0.125963:+1600+0:tile004.png
0.128795:+800+1200:tile020.png
0.133506:+0+400:tile006.png
0.139894:+1600+400:tile010.png
0.143205:+2000+2800:tile047.png
0.144552:+400+2400:tile037.png
0.153143:+0+0:tile000.png
0.154167:+400+400:tile007.png
0.173786:+0+2400:tile036.png
0.17545:+400+1600:tile025.png
0.193964:+2000+400:tile011.png
0.209993:+0+3200:tile048.png
0.211954:+1200+800:tile015.png
0.215337:+400+2000:tile031.png
0.218159:+800+1600:tile026.png
0.230095:+2000+1200:tile023.png
0.237791:+2000+0:tile005.png
0.239336:+2000+1600:tile029.png
0.24275:+800+2400:tile038.png
0.244751:+0+2000:tile030.png
0.254958:+800+2000:tile032.png
0.271722:+2000+2000:tile035.png
0.275329:+0+1600:tile024.png
0.278992:+2000+800:tile017.png
0.282241:+400+1200:tile019.png
0.285228:+1200+1200:tile021.png
0.290524:+400+800:tile013.png
0.320734:+0+800:tile012.png
0.330168:+1600+2000:tile034.png
0.360795:+1200+2000:tile033.png
0.391519:+0+1200:tile018.png
0.421396:+1200+1600:tile027.png
0.421421:+2000+2400:tile041.png
0.421696:+1600+2400:tile040.png
0.486866:+1600+1600:tile028.png
0.489479:+1600+800:tile016.png
0.611449:+1600+1200:tile022.png
0.674079:+1200+2400:tile039.png
and, hey presto, the last one listed (i.e. the one with the highest entropy) tile039.png is this one.
I have drawn a rectangle around its location using this command
convert image.png -stroke red -fill none -strokewidth 3 -draw "rectangle 1200,2400 1600,2800" a.jpg
I concede there may be luck involved, but I only have one image to test my mad theories. You may need to tile twice, the second time with an x-offset and y-offset of half a tile width, so that you don't cut the QR code and split it across 2 tiles. You may need different size tiles for different size barcodes. You may need to consider the last 3-5 tiles located for your next algorithm. But I think it could form the basis of a method.
Related
Using ImageMagick or GhostScript or any PHP code how can I get the DPI value of PDF files?
Here is the link for two demo files
http://jmp.sh/O5g5wL4 -- of 72 DPI
http://jmp.sh/RxrnYrY -- of 300 DPI
I have used
$image = new Imagick();
$image->readImage('xyz.pdf');
$resolutions = $image->getImageResolution();
It gives the same result for two different PDF files having different DPI.
I have also used
pdfimages -list xyz.pdf
It gives a list of all information but how to fetch the DPI value from the list.
How to get the exact DPI value of a PDF?
As fmw42 says PDF files themselves have no resolution. However in your case both the files consist of nothing but an image. In one case the image is ~48 MB and in the other its around 200 MB.
The reason is that the images have a different effective resolution.
In PDF the image is simply a bitmap, a sequence of coloured pixels. These are then drawn onto the underlying media. At this point there is no resolution, the pixels are laid down in a specific media size. In your case 22 inches by 82 inches.
The effective resolution is given by dividing the dimension by the number of pixels in the image in that dimension.
So if I have an image which is 1000x1000 pixels, and I draw it in a 1 inch square, then the effective resolution of the image is 1000 dpi. If I change my mind and draw it in a square 4 inches by 4 inches, then the effective resolution is 250 dpi.
The image hasn't changed, just the area it covers.
Now consider I have two images drawn in 1 inch squares. the first image is 1000x1000, the second is 500x500. The effective resolution of the first image is 1000 dpi, the effective resolution of the second is 500 dpi.
So you can see that, in PDF, the effective resolution of the image is a combination of the dimensions of the image, and the dimensions of the media it covers.
That's a difficult thing to measure in a PDF file. The area covered is calculated using matrix algebra and can be a combination of several different matrices.
The actual dimensions of the image, by contrast are quite easy to determine, they are given in the image dictionary. Your images are: 1620x5868 and 3372x12225. In both cases the media is the same size; 22.5x81.5 inches.
Since the images cover the entire media, the effective resolutions are;
1620/22.5 = 72 by 5868/81.5 = 72
3372/22.5 = 149.866 by 12225/81.5 = 150
I think MuPDF will give you image dimensions and media dimensions, assuming all your PDF files are constructed like this you can then simply perform the maths, but note that this won't be so simple for ordinary PDF files where images don't cover the entire media.
Using mutool info -I -M 150-dpi.pdf gives:
Retrieving info from pages 1-1...
Mediaboxes (1):
1 (6 0 R): [ 0 0 1620 5868 ]
Images (1):
1 (6 0 R): [ DCT ] 3375x12225 8bpc DevCMYK (12 0 R)
So there's your image dimensions and your media size. All you need to do is apply the division of one by the other.
Note: In debian and related distros, mutool is contained in mupdf-tools package, not in mupdf package itself. It can by therefore installed by sudo apt install mupdf-tools.
I use pdfimages -list from the poppler library, gives you all the information about the images.
I've got a 8.5x11 PDF at 300dpi. It has a single UPC label in the top left corner of the PDF. Imagine that there could be 30 labels on a 1 sheet, but we just have 1 label.
I'm trying to crop the PDF to be just the size of the 1 label. So far I've got this
gm convert -density 300 single.pdf out.pdf
Which doesn't do any cropping. When I crop to say 300x100 it makes a 20MB file with 30000 pages.
I have not a clue how to use -crop to actually crop to the correct size. I need it to be 3.5inches by 1.125 inches.
Using the following input PDF (here converted to a PNG):
the following command will crop the label:
gm wiz.pdf -crop 180x50+1+1 cropped.pdf
This label is sized 180x50 pixels.
For an 8.5x11in PDF at 300 PPI you'd have a 2450x3300 pixels PDF (which I doubt you do, but that's another question) and you'd need to use -crop 1050x337+0+0 (more exactly, 1050x337.5+0+0 -- but you cannot crop half pixels!).
Note, the +0+0 part crops the top left corner. If you need offset to the right by N pixels and to the bottom by M pixels use +N+M...
Using ImageMagick instead...
You could also use ImageMagick's convert command:
convert wiz.pdf[180x50+1+1] cropped.pdf
Comment about image sizes...
One additional comment about this remark:
"I have not a clue how to use -crop to actually crop to the correct size."
There is no other real size for raster images than pixels. ABC pixels wide and XYZ pixels high...
There is no such thing as an absolute, real size for a digital image that you can measure in inches... unless you additionally can state the resolution at which a given image is rendered on a display or a print device!
An 8.50x11in sized image at 300 PPI will translate to 2550x3300 pixels.
However, if your image does not contain this amount of pixels (which is the real, absolute size of any raster image), you may still be able to render it at 300 PPI -- but its size in inches will be different from 8.5x11in!
So, whenever you want to crop, use the absolute number of pixels you want. Don't use resolution/density at all on your command line!
What i say in the title is what i'm doing manually right now for 30 levels!
I'm building different color tshirt previews, every level represents a color and there's a level on top with the draw to be printed.
If I can do it automatically I'll have lot of time saved!
Anybody can help?
Use convert from the ImageMagick tools:
convert multilayer.xcf output.png
The result will be a separate PNG for each layer:
output-0.png
output-1.png
output-2.png
[…]
And: don't use JPG if you continue to print it on T-Shirts… JPG is lossy and doesn't support alpha-channels, which is important for most T-Shirt prints.
i want to shrink png or jpg on OSX. i only want to shrinkg without affecting the image quality.
like tinypng.org
is there any recommended library? i just know imagemagick. is there a way to do that natively? or another library to shrink/compress images without affecting the image quality?
my aim is to shrink the file size, for example:
logo.png >> 476 k before shrink
logo.png >> 50k after shrink
Edit: to be clear, i want to compress the size of the file, not the image resolution.
TinyPNG.org works by using image quantisation - the similar colours in the image are converted into a HSV or RGB model and then merged depending on the distance.
How does it work?
...
When you upload a PNG (Portable Network Graphics) file, similar colours in your image are combined. This technique is called “quantisation”
...
src: http://tinypng.org
An answer here outlines a method of doing so: https://stackoverflow.com/a/492230/556479.
There are also some answers on this question with refer to how you can do so on Mac OS using objective-c: How do I reduce a bitmap to a known set of RGB colours
See Wikipedia for a more in depth guide: http://en.wikipedia.org/wiki/Color_quantization
Did you have a problem using ImageMagick? It has a rich set of quantize functions such as
bool MagickQuantizeImage( MagickWand mgck_wnd,
float number_colors,
int colorspace_type,
float treedepth,
bool dither,
bool measure_error )
Here is a very thorough guide to quantization using imageMagick
My suggestion is to use http://pngnq.sourceforge.net, it will give better results than ImageMagick and for the single example given in http://tinypng.org, it also produces a very similar output. It is a tiny C implementation of the method present in the paper "Kohonen Neural Networks for Optimal Colour Quantization". That alone is much better since you are no longer relying on closed unknown implementations.
Original (57 KB), tinypng.org (16 KB), pngnq (17 KB):
Using ImageMagick, the best quantization to 256 colors I can get uses the LAB colorspace and dithering by Floyd-Steinberg:
convert input.png -quantize LAB -dither FloydSteinberg -colors 256 output.png
This produces a 16 KB png, but it contains much more visual artifacts:
I have a camera which produces photographs of 3008x2000 pixels. I use Image Magick to scale and resize the photos to be put up on my website. The size of the images I am using on the website is 602x400. I use this command to reduce the size:
convert DSC_0124.JPG -scale 20% -size 24% img1.jpg
This produces an image which is 602x400 pixels in size. But the file size will be always above 250KB. More images on a single html page means the page will be heavier and loading time will be longer. Are there any features in image magic that will help me to keep the file size as small as possible, possibly, below 100KB. But the image size should be the same, that is, 602x400px. I have achieved similar optimisation with SEAMonster tool for MS Windows. As it doean't have a commandline alternative, it wouldn't be of much help when there are hundreds of images to be converted.
Use command as Delan proposed with additional "-strip" flag to remove EXIF data, this have reduced the size of some of my images drastically. Here is a bash script for unix platforms, but you can use the second part only for individual images.
for X in *.jpg; do convert "$X" -resize 602x400 -strip -quality 86 "$X"; done
This will convert all images in the directory.
Use -quality to set the compression level:
convert DSC_0124.JPG -scale 20% -size 24% -quality [0..100] img1.jpg
You can define the maximum size of the output image at 100KB like this:
convert DSC_0124.JPG -resize 602x400! -strip -define jpeg:extent=100KB img1.jpg
If you are running your website on PHP, you might want to consider the SLIR image resizing script, it does a great job resizing to various constraints (see below) and caches the results.
Parameters:
w Maximum width
h Maximum height
c Crop ratio
q Quality
b Background fill color
p Progressive
http://shiftingpixel.com/2008/03/03/smart-image-resizer/
http://code.google.com/p/smart-lencioni-image-resizer/