RAW Image Files - please explain

I am correct in assuming the following about RAW image files.

RAW image files must be converted to say a jpeg or tif in order to be
processed in an image software package (eg Photoshop) for printing.

Or can RAW files be processed/manipulated as RAW files and then converted to
jpeg.

I keep hearing about RAW convertors but I don't understand when the
convertor is used and why.

Is it used before you can do any processing of the image or can the RAW
image be processed without any conversion?

Does conversion mean saving as a jpeg or tif or bmp?

regards

PeterH

The earlier post should read "Am I correct in assuming the following about
RAW image files?"

PeterH


"PeterH" reply to wrote in message
...
I am correct in assuming the following about RAW image files.

"Gareth Tuckwell" wrote in message
...

JPG is an acronym (anyone?). It applies an algorithm to the raw bitmap

Joint Photographic Experts Group, thus, more correctly, JPEG.

"Gareth Tuckwell" wrote in message
...

JPG is an acronym (anyone?). It applies an algorithm to the raw bitmap

Joint Photographic Experts Group, thus, more correctly, JPEG.

Raw image format is pure bitmap - no compression. I don't think RAW is an
acronym (I might be wrong), but I think it simply means the original and
uncompressed 'raw' image.

JPG is an acronym (anyone?). It applies an algorithm to the raw bitmap
image, discarding information that the human eye does not need to see in
order to understand the image, therefore the end result is an image with
less information, that looks almost identical to the original, but takes up
less file space.

You should work with (crop, colour adjust etc.) the original high quality
bitmap (raw) image and only as a last stage (if at all) should
you save using a compression algorithm such as JPG or GIF.

Photoshop, Paint Shop Pro and all photo manipulation software should be able
to work with raw images - I don't have a digital camera, only film + a
scanner, so I don't know what the files are called when you upload them to
your PC, but raw files should open as 'bitmaps'.

You can try this - take a copy of a bitmap file and do some work on it -
resize it a few times, then perhaps a crop, saving it after each operation
(as bitmap). Take a copy of the same original file and immediately save it
as a JPG, then repeat the resize, crop etc operations, again saving them
each time (as JPG). Once you have done a few operations on the JPG files you
will start to see the compression having an effect on the image quality - it
starts to look blotchy and smudged, whereas the bitmap version should still
be perfectly sharp and clear. This is why you should work with bitmap (raw)
images and save them with compression only at the end.

If you look in the help system for your photo software, or even a quick
search online, you will be able to read about the various compressions -
BMP, GIF, JPG, TIFF etc.



"PeterH" reply to wrote in message
...
I am correct in assuming the following about RAW image files.

RAW image files must be converted to say a jpeg or tif in order to be
processed in an image software package (eg Photoshop) for printing.

Or can RAW files be processed/manipulated as RAW files and then converted
to
jpeg.

I keep hearing about RAW convertors but I don't understand when the
convertor is used and why.

Is it used before you can do any processing of the image or can the RAW
image be processed without any conversion?

Does conversion mean saving as a jpeg or tif or bmp?

regards

PeterH

To understand RAW files, it is best to first look at the steps the camera
takes in creating the image. Firstly the sensor - each sensel (sensor
element) in the camera records either red, green or blue. The normal pattern
has red, green and blue in the ratio of 1:2:1. When you take a picture, the
CCD returns an analogue voltage for each of the sensels. This voltage gets
converted to a digital value (anywhere from 8 to 16 bits resolution) which
is associated with each sensel. This information is what goes into the raw
file. At this stage there has been no digital manipulation at all.
Practically all cameras will then take this raw data, and start processing
it. The camera will look at each sensel's neighbours, and interpolate a full
colour value for the resulting pixel in the output image. Depending on the
camera it may at this point enhance colour to give better saturation. At
this point the image could be downsampled to 24bit and saved as a TIFF
image. Most cameras then convert to JPEG prior to saving on the card.
Comments about your post are now sprinkled through....

"PeterH" reply to wrote in message
...
I am correct in assuming the following about RAW image files.

RAW image files must be converted to say a jpeg or tif in order to be
processed in an image software package (eg Photoshop) for printing.
Yes.

Or can RAW files be processed/manipulated as RAW files and then converted
to
jpeg.
Some manipulation could possibly be done as RAW but it wouldn't be normal.
RAW doesn't actually contain a usable image, it just consists of a bunch of
values representing either Red, Green or Blue depending on which colour the
particular sensel is.

I keep hearing about RAW convertors but I don't understand when the
convertor is used and why.
As one of the first steps - to convert the image into a usable image that
has RGB values for each pixel.

Is it used before you can do any processing of the image or can the RAW
image be processed without any conversion?
In theory some processing could be done on the RAW image, as long as the
program doing the processing understands that particular cameras image.

Does conversion mean saving as a jpeg or tif or bmp?
Conversion means converting to an image with RGB values at each pixel - once
that has been done it could be saved in any image format.

regards

PeterH

To understand RAW files, it is best to first look at the steps the camera
takes in creating the image. Firstly the sensor - each sensel (sensor
element) in the camera records either red, green or blue. The normal pattern
has red, green and blue in the ratio of 1:2:1. When you take a picture, the
CCD returns an analogue voltage for each of the sensels. This voltage gets
converted to a digital value (anywhere from 8 to 16 bits resolution) which
is associated with each sensel. This information is what goes into the raw
file. At this stage there has been no digital manipulation at all.
Practically all cameras will then take this raw data, and start processing
it. The camera will look at each sensel's neighbours, and interpolate a full
colour value for the resulting pixel in the output image. Depending on the
camera it may at this point enhance colour to give better saturation. At
this point the image could be downsampled to 24bit and saved as a TIFF
image. Most cameras then convert to JPEG prior to saving on the card.
Comments about your post are now sprinkled through....

"PeterH" reply to wrote in message
...
I am correct in assuming the following about RAW image files.

RAW image files must be converted to say a jpeg or tif in order to be
processed in an image software package (eg Photoshop) for printing.
Yes.

Or can RAW files be processed/manipulated as RAW files and then converted
to
jpeg.
Some manipulation could possibly be done as RAW but it wouldn't be normal.
RAW doesn't actually contain a usable image, it just consists of a bunch of
values representing either Red, Green or Blue depending on which colour the
particular sensel is.

I keep hearing about RAW convertors but I don't understand when the
convertor is used and why.
As one of the first steps - to convert the image into a usable image that
has RGB values for each pixel.

Is it used before you can do any processing of the image or can the RAW
image be processed without any conversion?
In theory some processing could be done on the RAW image, as long as the
program doing the processing understands that particular cameras image.

Does conversion mean saving as a jpeg or tif or bmp?
Conversion means converting to an image with RGB values at each pixel - once
that has been done it could be saved in any image format.

regards

PeterH

Thanks Justin - great reply.

Makes more sense now.

regards

PeterH

PS - can you also help me with my second post to this NG re "Canon RAW with
JPG Embedded"?


"Justin Thyme" wrote in message
...
To understand RAW files, it is best to first look at the steps the camera
takes in creating the image. Firstly the sensor - each sensel (sensor
element) in the camera records either red, green or blue. The normal
pattern
has red, green and blue in the ratio of 1:2:1. When you take a picture,
the
CCD returns an analogue voltage for each of the sensels. This voltage gets
converted to a digital value (anywhere from 8 to 16 bits resolution) which
is associated with each sensel. This information is what goes into the raw
file. At this stage there has been no digital manipulation at all.
Practically all cameras will then take this raw data, and start processing
it. The camera will look at each sensel's neighbours, and interpolate a
full
colour value for the resulting pixel in the output image. Depending on the
camera it may at this point enhance colour to give better saturation. At
this point the image could be downsampled to 24bit and saved as a TIFF
image. Most cameras then convert to JPEG prior to saving on the card.
Comments about your post are now sprinkled through....

"PeterH" reply to wrote in message
...
I am correct in assuming the following about RAW image files.

RAW image files must be converted to say a jpeg or tif in order to be
processed in an image software package (eg Photoshop) for printing.
Yes.

Or can RAW files be processed/manipulated as RAW files and then
converted
to
jpeg.
Some manipulation could possibly be done as RAW but it wouldn't be normal.
RAW doesn't actually contain a usable image, it just consists of a bunch
of
values representing either Red, Green or Blue depending on which colour
the
particular sensel is.

I keep hearing about RAW convertors but I don't understand when the
convertor is used and why.
As one of the first steps - to convert the image into a usable image that
has RGB values for each pixel.

Is it used before you can do any processing of the image or can the RAW
image be processed without any conversion?
In theory some processing could be done on the RAW image, as long as the
program doing the processing understands that particular cameras image.

Does conversion mean saving as a jpeg or tif or bmp?
Conversion means converting to an image with RGB values at each pixel -
once
that has been done it could be saved in any image format.

regards

PeterH

"Gareth Tuckwell" wrote in message
...
Raw image format is pure bitmap - no compression. I don't think RAW is an
acronym (I might be wrong), but I think it simply means the original and
uncompressed 'raw' image.

The image may very well be (and mostly is) compressed, but with a lossless
compression algorithm. In the camera world, RAW means unprocessed CCD output
data. These files are mostly if not always of proprietary formats and
require vendor specific converters. Most converters have plenty settings for
post processing during conversioin (white balance, sharpening, saturation
and so on).

The main reason I use RAW is that the format has more bits per channel and
opens for more precise color correction and better dynamic range than 8
bits/channel. My camera has 10 bits/channel in RAW. Better cameras typically
have 12. I convert my images to 48 bit TIFF and process those in Photoshop
CS. At the very end I change to 24bit JPEG or TIFF depending on use.

To me, RAW is power. To others it implies a workflow that is too complex for
their needs/ability/interest.

/Helge

"Gareth Tuckwell" wrote in message
...
Raw image format is pure bitmap - no compression. I don't think RAW is an
acronym (I might be wrong), but I think it simply means the original and
uncompressed 'raw' image.

The image may very well be (and mostly is) compressed, but with a lossless
compression algorithm. In the camera world, RAW means unprocessed CCD output
data. These files are mostly if not always of proprietary formats and
require vendor specific converters. Most converters have plenty settings for
post processing during conversioin (white balance, sharpening, saturation
and so on).

The main reason I use RAW is that the format has more bits per channel and
opens for more precise color correction and better dynamic range than 8
bits/channel. My camera has 10 bits/channel in RAW. Better cameras typically
have 12. I convert my images to 48 bit TIFF and process those in Photoshop
CS. At the very end I change to 24bit JPEG or TIFF depending on use.

To me, RAW is power. To others it implies a workflow that is too complex for
their needs/ability/interest.

/Helge