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Re: JPEG2000 compression [message #43457 is a reply to message #41151]

Thu, 14 April 2005 07:41

Emmanuel Christophe is currently offline

Emmanuel Christophe
Messages: 11
Registered: March 2004

Junior Member

Roberto Monaco a ï¿½crit :
> I have a question regarding JPEG2000:
>
> How do you control compression ratio when you save an image as JPEG2000
> using the IDL object?
>
> The following is curious: within a Photoshop plug-in I use to save JPEG2000
> images, "they" define a compression factor. If I save the same image with
> different compressions ratios (e.g. 1:1, 1:10, 1:40) I obviously get big
> differences in the resulting file sizes. But if you read these files into
> IDL objects, surprisingly all properties are exactly the same!! Same
> dimensions for the data array, same bit_depth, same number of layers, etc.
> ?? This does not make any sense to me ... I must be overlooking at something
> stupid?
>
> Thanks for any tips.
> Roberto
>
>

I got this problem before, I only manage to get lossless jpeg2000
compression directly with IDL. I went around this problem by calling one
free implementation of jpeg2000 (using spawn): jasper

;creating source j2k file from idl data (image)
im_jpeg=obj_new('IDLffJPEG2000',filenamesrc,/write)
im_jpeg->SetProperty, bit_depth=16, signed=1, reversible=1
im_jpeg->SetData, image
OBJ_DESTROY, im_jpeg

;compressing file
spawn,'jasper -f '+filenamesrc+'-F '+filenamenew+' -T jpc -O rate=0.2'
;reopening in IDL
im_jpeg2=obj_new('IDLffJPEG2000',filenamenew,/read)
imnew=intarr(ns,nl)
imnew=im_jpeg2->GetData()

Hope this help,
Emmanuel

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[Message index]

		JPEG2000 compression ratios? By: Matt Feinstein on Wed, 29 September 2004 05:14
		Re: JPEG2000 compression By: Emmanuel Christophe on Thu, 14 April 2005 07:41
		Re: JPEG2000 compression By: Rick Towler on Wed, 13 April 2005 16:27
		Re: JPEG2000 compression By: Roberto Monaco on Wed, 13 April 2005 12:55
		Re: JPEG2000 compression By: Rick Towler on Wed, 13 April 2005 09:24

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