Color vs Grayscale

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Color vs Grayscale

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seagrave

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13. March 2010 @ 13:25

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If color is 24bit and grayscale 8bit... does it stand to reason that a B&W file encoded as color will be 3 times larger for the same quality?

On a side note... how can one tell from an existing video file whether it was encoded as grayscale? I find nothing in file properties and nothing in GSpot... and least nothing that stands out.

Thanks!

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seagrave

Member

13. March 2010 @ 15:23

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Damn... I did a test using TMPGEnc encoding a B&W source to DIVX in both color and what I hoped was true grayacale (turning down the chroma) but the final file sizes were the same.

So I did a test in Handbrake which does have a true grayscale option... this time to AVC... and again the file sizes were the same.

Oh well... I thought I could get better compression on B&W videos using grayscale... but I guess not. Or am I missing something?

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This message has been edited since posting. Last time this message was edited on 13. March 2010 @ 15:52

scum101

Suspended due to non-functional email address

14. March 2010 @ 14:20

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what are you missing hmm#?.. want a clue?.. file size has everything to do with number of pixels and average levels (actually amount of change of levels between each frame.. why analog video captures are huge until processed).. and nothing at all to do with colour... A file of black will be the same size as white will be the same size as red.. or blue.. or any other colour you want to pick.. it will also be very very much the same size as a still image video of the same run time... add motion and it will grow.. in proportion to the amount of detail and change between subsequent frames.

If you want to make a video file significantly smaller you have to sacrifice dynamic range.. detail.. or frame size

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http://www.gnu.org/philosophy/right-to-read.html
http://www.fsf.org/

This message has been edited since posting. Last time this message was edited on 14. March 2010 @ 14:21

davexnet

Senior Member

16. March 2010 @ 11:45

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Here's my understanding - even though you set grayscale, the encoder
still produces a 24-bit file.

Apparently earlier releases of Xvid included an 8-bit mode,
but it is no longer present.

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seagrave

Member

17. March 2010 @ 11:43

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Originally posted by scum101:
A file of black will be the same size as white will be the same size as red.. or blue.. or any other colour you want to pick.. it will also be very very much the same size as a still image video of the same run time... add motion and it will grow.. in proportion to the amount of detail and change between subsequent frames.

Greetings Scum101. What I was wondering about is in grayscale each pixel will be described in one of 256 values. In color each pixel is in RGB, each color with 256 values for that rough total of 17 million possible colors. It would SEEM that grayscale video should be 1/3 smaller that color. This is what happens in photos.

For example I just took a color image, and in Photoshop saved it as an uncompressed TIF. I got a 29276KB image.

I converted it to grayscale and saved it in the same manner and the size was the same. Which is more in keeping with what you suggested.

But when I chose another option and discarded the color information and again saved it as an uncompressed TIF, the resulting file was down to 9779megs. 9779x3=29337 which is right around 1/3 the size. This is what I expected.

So perhaps there's no true grayscale in video? It's merely a B&W image encoded as 8bit RGB?

Or is there a similar way in video to discard all that color information and reduce file size?

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seagrave

Member

17. March 2010 @ 11:44

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Originally posted by davexnet:
Here's my understanding - even though you set grayscale, the encoder
still produces a 24-bit file.

Apparently earlier releases of Xvid included an 8-bit mode,
but it is no longer present.

Thanks Davexnet. That explains everything!

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