OSCommerce Product Manager

OSCommerce Product Manager for Windows
Tasklist

FS#347 - Use JPEG downsampling when resizing the images.

Attached to Project: OSCommerce Product Manager
Opened by Mario A. Valdez-Ramirez (mvaldez) - Sunday, 22 July 2007, 13:06 GMT
Last edited by Mario A. Valdez-Ramirez (mvaldez) - Saturday, 11 August 2007, 09:00 GMT
Task Type New feature
Category Backend / Core
Status Closed
Assigned To Mario A. Valdez-Ramirez (mvaldez)
Operating System All
Severity Medium
Priority High
Reported Version any
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Test the downsampling options in the FreeImage library and test for different downsampling settings to check what options gives better size vs quality. The idea is to create an automatic downsampling selector based on the desired quality level defined in the OSCPMWin configuration.
This task depends upon

Closed by  Mario A. Valdez-Ramirez (mvaldez)
Saturday, 11 August 2007, 09:00 GMT
Reason for closing:  
Comment by Mario A. Valdez-Ramirez (mvaldez) - Saturday, 11 August 2007, 08:59 GMT
These are some posts I made at the FreeImage forum at SourceForge:


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JPEG chroma subsampling / downsampling
By: Mario A. Valdez-Ramirez (mvaldez) - 2007-07-26 07:21

Hi,

Does FreeImage do any chroma subsampling when saving a JPEG image? If yes, is there any way to tune it or is it done automatically depending on the quality setting? If not, is this a limitation of the libjpeg library?

Thanks in advance,

Mario A. Valdez-Ramirez.


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RE: JPEG chroma subsampling / downsampling
By: Hervé Drolon (drolonProject AdminAccepting Donations) - 2007-07-26 16:06

FreeImage uses the LibJPEG "high level API" to store images. What LibJPEG does behind the scene is unknown.
You should download the LibJPEG v6b from http://www.ijg.org/ and read the *.doc files. These files explain the capabilities of the library and all the configurable options that could be added into a higher level API such as FreeImage.

Hervé


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RE: JPEG chroma subsampling / downsampling
By: Mario A. Valdez-Ramirez (mvaldez) - 2007-07-26 20:06

Hi. Thanks for answering my question, Hervé. I am already checking the libjpeg library documentation as you suggest. I'll post what I find.

Regards,

Mario A. Valdez-Ramirez.


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RE: JPEG chroma subsampling / downsampling
By: Mario A. Valdez-Ramirez (mvaldez) - 2007-07-27 08:42

I found the libjpeg library defaults to a 2x2 (4:2:0) chroma downsampling/subsampling which produces the smallest JPEG files. I tested changing the chroma subsampling to 2x1 (4:2:2) and no subsampling at all (1x1 / 4:4:4) and found the image quality the same than 2x2, but these modes caused the image size to grow around 30 to 40% (at least in my test images).

Regards,

Mario A. Valdez-Ramirez.

Comment by Mario A. Valdez-Ramirez (mvaldez) - Saturday, 11 August 2007, 09:00 GMT

So, this is a Will Not Fix. Closing.

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