Resizing HDRI JPEG

[curly01]

Hi,


It might be perhaps a stupid question but. From what I know of JPEG - MPEG compression it works as follows. The codec divides the image in squares and looks in its lookup table the closest grayscale pattern that matches for each color channel. The images itself contains only references to that grayscale pattern. (Correct me if I'm wrong.) Beginning graphics designers sometimes tend to blow up (interpolate -> bilineair, cubic interpolation) the low res image to a high res images. This blurs out the image and you lose sharpness. By blowing up the image the grayscrale pattern becomes visible and you get these typical squares in an image. Is the same true for an HDRI JPEG?

[XDepthAdmin]

How jpeg works is described sufficiently well at Wikipedia: http://en.wikipedia.org/wiki/JPEG
As you can see the image undergoes "chroma subsampling", if that's what you refer to.
Then each YUV channel is DCT transformed.

By stretching up in resolution a jpeg-compressed image you might certainly worsen the chroma subsampling side-effects, resulting in something similar to "color bleeding", i.e. when color "areas" overflow to areas with a different color.

XDepth HDR behaves the same as a jpeg to this regard. Although chroma subsampling is an option in Jpeg; chroma subsampling options are: 4:4:4, 4:2:2 and 4:2:0. Their meaning is again at Wikipedia.
Currently XDepth HDR automatically handles chroma subsampling based on its quality factors, so it basically depends by the quality you save the image at.
If you save at 100% quality, you should not get worse results than stretching up any other type of image.
One thing to consider is, when you interpolate HDR data you get "blooming" effects due to interpolating high-value pixels. This happens even with uncompressed HDR images - and it's a natural and "wanted" behavior when dealing with HDR.

[curly01]

I know from my prepress background that in printing there is something called a gamut warning. When your image has colors that can't be represented in the color space CMYK for instance green screen green color (that's way to bright or other bright colors) you get a gamut warning indicating that the color can not be defined properly in the color space.

Is there something like that in HDRI?


Another question: What are the best monitor settings for viewing the HDR images?

[XDepthAdmin]

Simply put, there is no way you can "properly" view HDR images on a non-HDR display.
A good part of a HDR image can still be represented by the sRGB color space, but when it comes to very bright pixel values, you simply have to choose "an exposure" to view the whole image at - and the brightest pixels are shown in white.
There will be consumer-level HDR displays one day, probably sooner than later, where HDR luminance is properly represented.
On those displays, you will be able to appreciate all the contrast available in a HDR picture/movie, without the need of "exposing" the image.

Dolby Laboratories acquired such a technology not too long ago: http://www.dolby.com/promo/hdr/

[curly01]

Would you please post a list with available HDRI displays. (Otherwise I'll look it up on google.)

This one perhaps:
http://www.engadget.com/2008/03/31/sim2 ... prototype/

So, correct me if I'm wrong but HDRI contains much more color values then the human eye can distinguis. An HDRI display simply
maps the brightest and darkest values to a value the human eye can distinguis. (I hope I learned my lesson well. )
It would be nice to have a 30" lcd HDR screen for digital cinema (2K resolution) 2048 x 1080 pixels 24 frames per second progressive.


Another application of HDRI -> HDRI in games:

http://www.bit-tech.net/hardware/2005/1 ... _hdr_edr/1

(I'm interested in game programming -> where going to mess around with Blade3D or with Unity3D)
(Seems that you're technology has a much wider application then one would think.)

Have you already thought about medical imaging? ( X-RAYs are these days digital.)

[XDepthAdmin]

I imagine that's going to be the first HDR display - the one from Dolby - yes.
The HDR display works by boosting luminosity using ultra-bright LEDs. AFAIK they still have a couple of major flaws in their design though.
In theory an HDR "red" color, as an example, should be properly displayed over such a device, but apparently it comes out as a "bright white", instead as a "bright red"....the last time we saw it.
This is most probably because they lack a proper chroma encoding for their HDR compression system.

HDR and 48bit/pixel image and video compression have many applications, with medical image compression being one of those.
(and game development of course)

[curly01]

You're going to be able to buy a lot of Ferrari's with your technology if you play it smart.

[XDepthAdmin]

Oh, that would certainly not be me...but I will surely ask for a good raise.