[Tig] LUTs for Video File Codecs

Adrian Thomas adrian
Wed May 3 00:22:28 BST 2006

Thanks to oktobor for supporting the TIG

On May 2, 2006, at 22:53, Dan C. Tatut wrote:
> Photoshop has a tool that allows you to preview compressing for web- 
> like image formats (e.g. JPEG, GIF). What actually Photoshop does,  
> is compressing the image in memory and decompressing it again and  
> display the result. This is the preview of the compressed file.

Many compression tools do likewise, but this feature has limited  
value when using multi-pass VBR CODECs.

> Another issue is that all the codecs tend to have their own tricks  
> to compress images. There is no rule in image compression... that's  
> why you have so many available.
> Ideally one should output the media and send it to a compressor,  
> decompress it again and compare differences. This can be achieved  
> by plugging your color grading system's SDI output into a real-time  
> MPEG encoder for example, then plug the output into a real-time  
> MPEG decoder and feed-back the color grading system with the  
> result. Not so easy but feasible.

Feasible indeed, but probably of zero practical value. Even different  
encoders targeting the same CODEC - and for pedantry's sake neither  
QuickTime nor Windows Media are CODECs - give wildly differing  
results. The best course is to grade as normal and give your  
compressionist a solid, consistent target to aim at.

Adrian Thomas
+44 (0) 20 7240 2073

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