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Re: [OM] Spotmeters

Subject: Re: [OM] Spotmeters
From: Moose <olymoose@xxxxxxxxx>
Date: Thu, 26 Feb 2015 13:20:20 -0800
On 2/26/2015 8:04 AM, Chris Trask wrote:
....
      I'm going to again disagree here.  In the E-500, an ORF file is 13.6M, 
whereas a TIFF file is 24M.  Since the sensor itself has approximately 8MP and 
3 bytes/pixel (or 1 byte/colour/pixel or 24 bits/pixel), the dead-nuts raw data 
from the sensor is  approximately 24M, the same size as the TIFF file.

Once again into the breach. You are WRONG, WRONG, WRONG!!!

The data from the sensor in a Bayer array camera, which is what you have, and indeed the vast majority of digital cameras, is one value per pixel. That's it, all there is at the sensor level, an individual light measuring semiconductor junction behind a colored filter, recording the level of light that fall on it. And that's what is recorded in the RAW file.*

Three values per pixel doesn't exist until the RAW file has been converted. It is data derived by computation from the RAW data.. However, the data values in the RAW file consist of 12 bits, not 8. Depending on how data data is encoded, that may mean two bytes per pixel or three bytes per two pixels.

THE RAW FILE IS THE SOURCE! It IS "... the dead-nuts raw data from the sensor ..." It is as close to the actual data read off the sensor as it is possible to get. ANY derivative format contains slightly less accurate data about the light that hit the sensor.

The data from RAW conversion varies with different converters. Just this morning, I received a promotional email from PhaseOne, claiming superior color in RAW conversion from their software to that made by others. And there is a slight, but noticeable, difference in the samples in the email, even in small JPEGS on the web. As I recall, AG agrees with them about skin color accuracy from most RAW formats.

That being the case, I'm making a safe assumption that the TIFF format is the 
ultimate RAW format

NOT, NOT NOT a safe assumption! Your confusion of size with amount of 
information is WRONG!

  (no compression and hopefully no processing),

Where do you come up with this stuff????? An eight bit TIFF file has been heavily processed, and data has been thrown away. First, the single color pixels have become three value pixels by calculating imputed values from adjacent/nearby pixels of the other colors, together with its own single color brightness.

In addition, the 12 bits of brightness data for the single color sensed by each pixel has been processed into 8 bits by literally throwing away information. (This is not true of all TIFF files. If you use ACR/LR, Oly Viewer, etc, and specify 16 bit output to a TIFF, you will get a 48 MB or larger output file, as you do below.)

whereas the ORF file is slightly compressed (but no processing).

Another place where a distinction must be made. Well, two, really:

1. You are assuming compression because the ORF file is smaller than the TIFF. If you understand the above, and the way sensors work, you will understand that a one value per pixel file may be smaller than a three value per pixel without compression or information loss.

2. There are two general categories of compression, and a third one of apparent 
compression.

a. Defined generic image file formats, TIFF, JPEG, PNG, PSD, and so on, are defined abound byte boundaries, and so come in 8, 16 and 32 bit per value varieties. In a proprietary format, such and Oly's ORF, Canon's RW2, etc., there is no need to waste space by adhering to byte boundaries. Data may be packed more efficiently. Packing is lossless, and is not compression, in the sense meant about image files.**

12 bit data values, such as used by all Oly sensor systems up until the E-M1, pack nicely, three data values in two bytes. Most RAW formats from various manufacturers use packing. It makes writing to the card faster and allows more images per card. (It is also FAR less processor intensive that actual compression.)

b. There is actual compression, as opposed to packing, that is lossless. Uncompression results in data exactly the same as the original. The TIFF format accommodates lossless, as well as lossy compression, depending on what the code writing the file does. I believe some RAW formats may do this. But it is processor intensive, and earlier camera processors are not particularly powerful or fast. I don't believe Oly uses it in their ORFs.

c. JPEG allows only lossy compression, although at the highest settings, the loss is minimal. TIFF MAY thus lose less information from the original than JPEG.

      I revisited my B&W experiments from last year and looked at the few ORF 
files I had saved.  I exported one as 16-bit TIFF (resulting in a 58M file) and 
viewed it in Corel PhotoPaint and DxO FilmPack.  The resolution was nice and crisp, 
but I would like to be able to bypass the ORF-to-TIFF conversion and record the 
same image as TIFF.

And I would like to be able to fly under my own power. Neither is possible. Unless, of course, you are able to hack the firmware code in your camera and rewrite it.

You are setting your cap for something unattainable, and actually not desirable, from a technical perspective. Basically, nobody, but for a few odd Oly 4/3 bodies, outputs TIFFs. And those are compromised in two ways:

1. They are eight bit.

2. They  bake in the RAW conversion algorithms of the time, while RAW 
conversion has improved since.

 And once they came to their senses, they quit.

      This may seem like a lot of work, but I am determined to find some way of 
overcoming the problems associated with taking digital B&W photos with glass 
Wratten filters.

Did you read my post on this subject? Look at the images?

Yes, I can presently do so by taking the best possible colour photo and then 
post-processing with FilterSim and DxO Filmpack, but I would really like to return 
to the hard-won expertise of taking good filtered B&W photos in the field.

And I've tried to show you how to do that, but it would appear that you aren't 
listening - or looking.

Tired of Obtuseness Moose

* You nit pickers, who claim that some processing occurs pre RAW file creation, please shut up for now. That a discussion for folks who know what a RAW file is.

** Back in the age of dinosaurs, when memory and disk storage space were at a premium, I was programming a data capture system. Many input fields were yes/no, binary. I packed eight of those into each byte of storage data. This was not compression - each piece of data still contained the same information. When unpacked, there was no difference from what was originally captured.

--
What if the Hokey Pokey *IS* what it's all about?
--
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