JPG based file does not activate JPG lossless operations..

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maadjordan
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JPG based file does not activate JPG lossless operations..

Post by maadjordan » Fri Oct 22, 2004 4:33 pm

i have a webshots image which it is a jfif-based(jpg-based) image file..
when you open the file .. lossless tools are OFF so nothing can be done..
-i renamed the file info JPG which should be useless (as Xnview is set to look for header..) and the status is same..
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helmut
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Re: 1.74 jpg based files does not activate lossless option..

Post by helmut » Sat Oct 23, 2004 9:12 am

maadjordan wrote:i have a webshots image which it is a jfif-based(jpg-based) image file..
when you open the file .. lossless tools are OFF so nothing can be done..
-i renamed the file info JPG which should be useless (as Xnview is set to look for header..) and the status is same..
I don't know whether there's a difference between JFIF and JPG. What happens if you unset the option "Recognize only by extension" (Tools/Options/File list)?

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maadjordan
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Post by maadjordan » Sat Oct 23, 2004 1:17 pm

its same with/without the option.. (tools/option/browser/filelist)
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ckit
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Post by ckit » Sun Oct 24, 2004 3:20 pm

Have you tried converting the jfif-based(jpg-based) file to a pure JPEG (make sure quality is set to 100%) and then use the Lossless tools.
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Post by Dreamer » Sun Oct 24, 2004 4:01 pm

ckit wrote:Have you tried converting the jfif-based(jpg-based) file to a pure JPEG (make sure quality is set to 100%) and then use the Lossless tools.
It should be working, but if he's got 50kb image, he convert it to 100% quality jpeg, size could be 150kb, so any lossless operations are useless then...

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maadjordan
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Post by maadjordan » Sun Oct 24, 2004 10:10 pm

convert it to jpg would not preserve quality even with your recommended setting..

i can dump (decode) it into jpg because webshots are an encoded jpgs.. so XnView should provide the lossless toolbar for any jpg-based files.. like webshots and others..
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ckit
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Post by ckit » Mon Oct 25, 2004 12:54 am

Sigh, you want quality you should be using BMP or PNG.
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Post by xnview » Mon Oct 25, 2004 7:39 am

maadjordan wrote:i can dump (decode) it into jpg because webshots are an encoded jpgs.. so XnView should provide the lossless toolbar for any jpg-based files.. like webshots and others..
Currently i can't make lossless transformations on jfif based files!
Pierre.

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maadjordan
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Post by maadjordan » Wed Oct 27, 2004 8:58 pm

so it would fall into TODO list :wink:
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Drahken
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Post by Drahken » Wed Aug 24, 2005 2:13 pm

Umm... for all practical purposes, jpg IS jfif.
JPEG itself specifies only how an image is transformed into a stream of bytes, but not how those bytes are encapsulated in any particular storage medium. A further standard, created by the Independent JPEG Group, called JFIF (JPEG File Interchange Format) specifies how to produce a file suitable for computer storage and transmission (such as over the Internet) from a JPEG stream. In common usage, when one speaks of a "JPEG file" one generally means a JFIF file
There are other types of jpgs available (spiff is the official type), but all standard jpgs that you see on the web and whatnot are jfif files. Spiff, for example, was created later by the original jpeg group and is the official standard (jfif is merely the de-facto standard), but very few applications can open a spiff file (and even fewer can create one).

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Drahken
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Post by Drahken » Tue Aug 30, 2005 9:44 pm

Some additional info on JFIF vs JPEG:
==========================
"JFIF" is the correct name for the image format commonly known as "JPEG." Strictly speaking, JPEG is a method of compression. The image format using JPEG compression that is by far the most common is JFIF. There is also a subformat of TIFF that uses JPEG compression.

EXIF is an image format that is a subformat of JFIF (to wit, a JFIF file that contains an EXIF header as an APP1 marker).

JFIF files can have either 8 bits per sample or 12 bits per sample. The 8 bit variety is by far the most common. There are two versions of the IJG JPEG library. One reads only 8 bit files and the other reads only 12 bit files.

There are two variations on the CMYK (and likewise YCCK) color space that may be used in the JFIF input. In the normal one, a zero value for a color components indicates absence of ink. In the other, a zero value means the maximum ink coverage. The latter is used by Adobe Photoshop when it creates a bare JFIF output file (but not when it creates JFIF output as part of Encapsulated Postscript output).
JFIF stands for JPEG File Interchange Format

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