I'm using an image loader (DevIL) for image loading. Im just wondering if the image format (the uncompressed format in memory) loaded from files (.jpg, .png, .bmp etc) is determined by the image loading program itself, or is some way contingent upon the actual image file.
All of the images I have looked at so far seem to be loaded into the RGBA / UNSIGNED_BYTE format. However I am wondering if I can always rely on this. Is it conceivable that an image might actually be loaded into the RGBA / FLOAT format instead? (NOTE: i am hoping that the loaded image format will always be the same, i want to rely on it:)
I can't find any docs in DevIL that explains this point, so I'm hoping anyone experienced with imaging / image loading could give me an answer just based on their experience / common sense.
Thanks
I don't know DevIL, but nearly any imaging library is going to provide you with an image object that has some concept of Pixel Format. The pixel format tells you how the image is laid out in memory. Looking quickly at the docs, I see that IlTexImage has a property called Format which can be one of IL_COLOUR_INDEX, IL_RGB, IL_RGBA, etc. The docs say
The format of the image data. Formats accepted are listed here and
are self-explanatory
Related
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'm trying to create a small PDF file, embedding one optimized PNG image displayed as a header and footer on a 3 page PDF (same image must appear 6x in the PDF)
My optimized PNG image is only 2.3KB. It looks very sharp.
Failed with libreoffice
When I insert just one instance of the 2.3KB PNG image into a Libreoffice Writer doc containing only text, then export as PDF I can see that the image gets re-compressed to JPG and the resulting PDF file grows by about 40KB after adding the image. It also loses quality, the PNG also gets JPG fuzzy edges.
If I right click the image and select compression, there is no way to disable recompressing the image (it's already optimized better than libreoffice could do it) I've tried setting a compression level of 0,1,9 etc. Choosing JPG, no resize, lossless, etc but there was no improvement.
Failed with wkhtmltopdf
I also tried making a test page and used wkhtml2pdf but it did the same thing. Adding the low quality flag made no difference.
PDF Spec suggests PNG is supported?
From skimming the PDF spec, it looks like PNG images are supported.
Even plain text PDF files are surprisingly large
The disappointing thing is also when I take a 7KB HTML file which is basically just <html><body><p>foo...</p><p>bar...</p> (only about 15 paragraphs) with no CSS. The resulting 2 page PDF file is 30KB. Why should a 7kb (almost plain text) file become 30kb as a PDF?
Suggestions?
Can someone please suggest how to make a small PDF file in Linux?
I need to include 7KB of text and repeat one PNG image 6 times.
Manually or programatically. I'll take whatever I can get at this point.
PDF Spec suggests PNG is supported?
PNG isn't supported per se; PDF allows embedding JPEG images as-is, but not PNG images. PDF does borrow a set of features of the PNG format, however.
rinohtype (full disclosure: I'm the author) tries to embed as much as possible from PNG images as-is into the PDF. This does involve some bit-juggling to separate the alpha channel from the color data for example, but no reencoding of the image is performed. It does not (yet) support interlaced PNGs.
rinohtype should be able to do what you want to achieve. But please note that it currently is in a beta stage, so you might encounter some bugs.
Even plain text PDF files are surprisingly large
To keep the PDF size as small as possible, make sure not to embed/subset any of the fonts. Use only the fonts from the base 14 PDF fonts which are provided by PDF readers.
What you want is certainly achievable. Regarding the image quality, I would recommend making your image twice the size that you want it to actually display at in the PDF to keep it looking sharp.
As to the size, I've just modified a test in my PDF writer module (WIP..) to include a 7.2K png, 200px x 70px, in a PDF twice and the PDF came out at 6.8K 8). There's not much text included, but more text will only add what it's worth + a small percentage.
You can see the module and original test here.. https://github.com/DoccaPDF/docca-pdf-writer/blob/master/src/tests/writer.js#L40
That test adds ~112K of images to the PDF and results in a 103K PDF.
Of course not all images are created equal so you milage may vary..
*the images are only actually added to the PDF once, but are displayed multiple time.
I'm building a web application (RoR) that manages images that are in raw image format. I need to create thumbnail/web versions of these images to be displayed on the site. Currently, I'm using imagemagick, which delegates to dcraw to produce the jpeg thumbnail. The problem I'm running into is that the thumbnail deviates from the look of the original; the image gets darker and the white balance is sometimes heavily shifted.
I'm assuming that the raw format default setting can't be read by dcraw, and thus it's left guessing how to parameterize the raw conversion. I can play around with customizing these setting, but it seems getting it right on one image causes others to be further off the mark.
Is there a better way to do this in order to get a result that more closely mimics the what I might see in a raw viewer like photoshop, or even Mac OSX preview? Given that Mac OS X supports a variety of digital camera raw formats, is there anyway to utilize the OS's ability to render preview images (especially considering that result is what is expected).
The raw images that I'm using are 3FRs and fffs (both from Hasselblad).
I can post samples if people are interested.
Thanks
Look at "sips" and "Resizing images using the command line" to get you started.
Sometimes when I see a lower resolution load before I see the full image. This is not done in jQuery as it also happens when you load the image stand-alone. I have not a single idea how they do this, but I guess it's something server side.
My question is, how would I do this on my own server?
The images are stored in "progressive" or "interlaced" JPEG format, meaning that the low-res image data is stored before the high-res data (in layman's terms). You can encode any JPEG as interlaced. You can even do it on the server using imagemagick.
Here's Jeff Atwood talking about this.
I use Abbyy FineReader for ScanSnap to OCR a couple of scanned PDF files. The software claims it retains the original PDF images. The PDF file sizes pre-OCR and post-OCR are almost identical, which is good.
After the software is done, all PDF images appear anti-aliased in Acrobat X. Page navigation is much slower than before, and when I zoom in/out, the images first go to what looks like the pre-anti-aliasing version before quickly changing to anti-aliased images.
Left: Scanned PDF / Right: after OCR with Abbyy
I would like to get the original images without anti-aliasing back. Interestingly, when I open a single page from the anti-aliased PDF in Photoshop, there is no anti-aliasing and the image looks like the left one.
My limited PDF programming experience leads me to believe that Abbyy likely sets some kind of anti-alias flag for each image during OCR processing. How do I un-set this flag?
Any pointers to useful ideas would be much appreciated.
After the software is done, all PDF images appear anti-aliased in Acrobat X. Page navigation is much slower than before, and when I zoom in/out, the images first go to what looks like the pre-anti-aliasing version before quickly changing to anti-aliased images.
Actually in the original file 2013_11_15_22_51_31.pdf contains a JPEG image while the OCR'ed file 2013_11_15_22_51_31_OCR.pdf contains a JPEG2000 image.
Comparing them in third party viewers, it becomes clear that the image in the OCR'ed file is not inherently anti-alias'ed. Furthermore there is no evident flag in the PDF instructing PDF viewers to apply anti-aliasing to the JPEG2000 image. Thus, Adobe Reader seems to automatically render JPEG and JPEG2000 images differently, applying anti-aliasing to the latter but not to the former.
Comparing both images in detail, though, it becomes clear that these images are not identical but instead the image in the OCR'ed PDF is slightly rotated.
I assume Abbyy FineReader recognized that the original scanned image is not correctly oriented. Thus, it rotated it slightly to correct this orientation.
Thus, replacing the image in the OCR'ed version with the one from the original one is no option: Due to the rotation the OCR information would partially be somewhat off.
What you might want to try is to recode the JPEG2000 image to JPEG and replace the image in the OCR'ed version with this recoded one. This will mean some loss of quality but most likely you can get rid of the anti-aliasing this way.
Be aware, though, that the JPEG2000 image is slightly larger than the JPEG image to accomodate for the rotation.
PS: As #VadimR pointed out, there is indeed an /Interpolate true entry in the image dictionary of the OCR-ed version I missed when looking at the file. This does not seem to be the major issue slowing down the rendering.
There is /Interpolate true entry in image dictionary of OCR-ed version, and that's what causes 'anti-aliasing'. Whether that (and not JPEG2000 instead of JPEG compression) is a cause of slow-down, you check on large enough files.
To un-set this key, the best would be to turn it off while creating a file, and if that's not possible, to write and run a small program in suitable language.
But, since your file doesn't sport 'compressed objects' and offending key is in plain view inside a file, in the spirit of 'job done quickly' you can simply process your file e.g. like this:
perl -M-encoding -0777pe "s!/Interpolate true!' 'x17!ge" <in.pdf >out.pdf