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A couple easy questions…
Posted by Yurii Hydrick on July 19, 2011 at 3:52 pmEasy for you guys. The first question is one I’ve been trying to find for a couple weeks now, just researching… In layman’s terms, what is gamma? I reiterate – in layman’s terms. Everywhere I’ve found always answers in an incomprehensible way – for me anyway.
Second question, is similar to the first. I keep seeing dpx file format… and though I understand that the concept is higher quality resolution per image… I’m not sure I understand the implications and process of what a dpx file is – or what they’re good for. Any help would be appreciated.
Best,
Yurii
Yurii
Yurii Hydrick replied 13 years, 3 months ago 4 Members · 7 Replies -
7 Replies
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Robbie Carman
July 19, 2011 at 7:25 pmYuri
I would suggest you pickup my good friend Alexis Van Hurkman’s book The Color Correction Handbook which you can find on Amazon. Alexis does a great job of going in to detail on these subjects and a whole lot more but in as you say “laymans” terms. Its a great read and will get you up to speed quickly.
Gamma is a deep subject that has many implications but put simply gamma is a non linear equal power adjustment. Often you’ll see gamma as it relates to a monitors non linear luminance response (2.2, 2.5 etc) in color grading to a non linear adjustment to mid tone contrast.
You should also check out the articles by Charles Poynton on the subject https://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html
DPX (digital picture exchange) is an uncompressed file format its often used when scanning film but its also used in high end digital recorder and as file exchange for VFX and of course in grading. While you can have a single DPX file they’re often grouped as image sequences. So for 1min of 24fps content you’d have 1440 individual frames or separate files. Its main advantages are in its high quality uncompressed nature but also how it can handle things like log image data.
Robbie Carman
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Colorist and Author
Check out my new Books:
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Yurii Hydrick
July 19, 2011 at 7:52 pmThanks Robbie! I’m going to look into Alexis’ book. I feel like I understand what it’s implications are (as I can see them obviously on the screen)… I just want to understand the color theory behind it all.
Thanks for answering about the dpx too. If you don’t mind me asking, how would it work into a workflow? Is it just a final output codec like ProRes, or more like an OMF (but for grading), or XML? I guess I’m just not understanding it’s place in a workflow.
Thanks again though, for helping.
Best,
Yurii
Yurii
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Robbie Carman
July 19, 2011 at 8:22 pmDPX can be input or output. For example you might have a project shot on film and using a datacine scaned to DPX files. From those DPX files you could create “offline” video files like ProRes etc to cut the story together and then in the finishing process in Resolve you could conform or relink back to the high quality DPX files.
Some editorial tools and plugins also allow you to edit with DPX files (glue tools for example enables this in FCP 7)
On the other end if you were doing a film out you’d most likely deliver DPX sequences for each reel of the film.
Its just another file format but a very high quality one. In fact if you want to play with DPX files to see how they can work download the AJA QT to DPX translator app from AJA (its free) and you can convert a QT to DPX and bring the image sequence into resolve. You can also of course output DPX from a project in Resolve.
Robbie Carman
—————-
Colorist and Author
Check out my new Books:
Video Made on a Mac
Apple Pro Training Series DVDSP
From Still To Motion -
Yurii Hydrick
July 19, 2011 at 9:13 pmGreat information. Thank you for your help, I appreciate it.
Best,
Yurii
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Fabio Cormack
July 20, 2011 at 12:14 amJust FYI, I bought this book today, Kindle version (for iPad) – excellent !
Fabio Cormack
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Robert Monaghan
July 20, 2011 at 2:12 pmHi Yurii,
Gamma is a way of adjusting an image, so that the image looks “right” in our brain. Computers (Cameras and scanners) all work best with a linear image. But when we look at a truly linear picture, it looks really dark to the human eye.
This is because Mother Nature has crafted our eyes to work best in Daylight. As a result, the majority of our eye’s receptors are set up to process brightly lit parts of an image, but darker parts are “flat”. (we have a hard time resolving details that darkly lit). — interestingly, there is an assumption that there is no details in the darks, simply because our eyes can’t see it. (Nocturnal animals have a different “Gamma”. They can see dark details better than they can see “daylight” details.)
So, what does this have to do with a Gamma Curve?
The Gamma curve is often a power function that draws a “curve”. Google “Gamma Curve” to see a graph.
When we take our gamma curve and apply it to the linear image, the lower 50% of the image’s brightness gets sharply contrasted, lifting/converting much of the darker pixel values into a broader range of low to mid tones. (for example, 18% grey – really dark in linear space, looks like it is actually 50% to our eyes.) The upper 50% of the image’s brightness looks really bright, even washed out in some cases.The resulting image looks “normal” to our eyes. Which is the main goal of a gamma curve.
Ok, why work in linear space, then? Well, the problem is that Computer Image processing algorithms and electronics, etc. all work best in linear space. Everyone and their dog has their own Gamma Curve. It is impossible to write mathematics to cover every type of Gamma curve. So linear is the best way to do image operations. (There are a number of other reasons for Linear, too. BTW.)
I hope this makes sense.
bob.
Robert Monaghan, CEO
Glue Tools LLC
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Yurii Hydrick
July 20, 2011 at 3:14 pmGreat explanation. Thank you Bob. I appreciate you, and everyone else on the forum, taking time to help me understand this better.
Best,
Yurii
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