How to convert scans to reasonable size?
First my environment:
Hardware: Epson Perfection V200 Photo scanner Software: xsane-0.995 (Linux) I scan magazines at 300dpi with this environment, which produces PNM files which are about 25MB (2544x3509 pixel, depth 24). Of course I can't (or am not willing) upload these images directly to an image hoster. Therefore I currently convert the images with the convert program from ImageMagick: convert -resize '1680x1680>' infile outfile.jpg; This produces images with a maximum side length of 1680 pixels, the image size is about 300 KB. My question: Is there a better way to compress the images to a reasonable size? |
I always batch-convert with GraphicConverter
PICT 32 bit -> jpeg |
Thanks for the response, butI have to rephrase my question: Is there a better way to get a better quality/image size (in bytes) ratio?
One example: I've converted the same scan with two different options to approximately the same size (380 kB): 1st Conversion: convert -resize '1680x1680>' page26.pnm page26-1680x1680.jpg (uses standard compression 85): http://img235.imagevenue.com/loc391/..._123_391lo.jpg 2nd Conversion: convert -quality 27 page26.pnm page26-q27.jpg (this sets the "JPEG compression" to 27 without changing the image size): http://img162.imagevenue.com/loc895/..._123_895lo.jpg Which one is better? Of course proposals for other programs which produce better results are welcome |
Panorama : resize / resample
http://img188.imagevenue.com/loc647/..._123_647lo.jpg left origin 95%, middle resize + zoom , right resample + zoom. ( irfanview ) The resample function in Irfanview softens during the resample and reduces the filesize. Panorama: jpg compression http://img257.imagevenue.com/loc370/..._123_370lo.jpg from left to right: 100%, 501KB 60%, 69KB 95%, 302KB 85%, 156KB It can be useful to save with high compression values ( 85%+ ) if the pic contains reflexions ( metal, fingernails, hair, ... ). Lower compression values decreases the depth effect due to lower brilliance. |
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I don't know about Linux, but I use Irfanview myself. IMO it produces very good results with the quality setting at 80%. |
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25MB
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Code:
> convert page26.pnm page26.bmp # converts PNM to BMP (lossless) PNM and BMP are almost the same formats, they store for every pixel the full information (e..g. 24 bits RGB value or 8 bit grey value). |
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The first picture. Why? Because the second picture has too many JPEG artifacts.(the Quality=27 is too low) There is a problem here, the first picture's size is 1218x1680 (resized 50%), the second picture's size is 2544x3509. It's not easy to compare them when they have different sizes. Is there a better way to get a better quality/image size (in bytes) ratio? No. If you want good quality you pay with a bigger file size. The JPEG compression is lossy, you can use it with Quality setting between 70-100, 85 is a good compromise. Some HQ (big sizes) examples: 1. 200dpi descreen on - 600kB http://img262.imagevenue.com/loc137/..._123_137lo.jpg 3. 300dpi descreen off, edited - 1MB http://img209.imagevenue.com/loc432/..._123_432lo.jpg 5. 300dpi descreen on, edited - 1MB http://img142.imagevenue.com/loc443/..._123_443lo.jpg It's interesting that the 300dpi pic with descreen ON has a little moire, and with descreen OFF no moire. Tuffy |
Back in the days when I was fiddling with these options, my rule of thumb was: scan with high resolution, reduce afterwards - although I left the reduction to a picture editor (PaintShop Pro), not the scanning software. Though this may have also been influenced by the tiny little issue that my first scanners didn't support picture reduction.:rolleyes:
Anyway, that strategy that seemed to help with Moire patterns. When I got Moire with scanning at 300dpi I moved to 500pdi or even 1000dpi, creating a monster-sized file, and then let the picture editor do its magic afterwards. |
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