"Kev" <(replacenumbersforletters)> wrote in message
Thanks for the explanation Mike,
Glad to help.
I’m sure you’ll have worked out by my 20MGPixel images that I have a 7mega pixel camera (7.2 to be exact, it’s the Sony Cyber-shot DSC-P200). I saved the file as Adobe TIFF after messing around with it.
I worked out it was bigger than my Nikon 😉
To print up to A4 size how would you suggest I save my files, as TIFF or JPEG? Maybe save as TIFF first and once manipulated return to JPEG to keep file sizes on hard drive to a minimum, or should I invest in a decent sized hard drive?
I save all my files as PSDs (TIFF as good or better as they don’t rely on Adobe to open) but print from JPGs.
I regulary print up to 20 x 16 (on line lab) and the quality is indistinguishable without a microscope. If you are home printing, run a copy of each off (TIFF versus JPG) and check for quality. More hard drives are always good for PS, but you could ( should?)always save your files to CD /DvD for security reasons (always make two copies) if nothing else. This would also free up space on your H/D.
If saving back to JPEG does the embedded information stay with the file or is it then lost?
It is exactlty the same situation as when you first opened the file from the camera, it is purely pixel dimension plus any compression applied to reduce file size.
You decide on the colour depth (1, 8 or 16 bit) when you open the file in something like PS.
Image mode isn’t "image information" (these are pixels) it is just a working/colour depth preference if you like.
Thanks again
You’re very welcome.
Mike
"Mike Hyndman" wrote in message
"Bill K" wrote in message
Mike Hyndman wrote:
"Kev" <(replacenumbersforletters)> wrote in message Hi,
I recently saved a JPEG from my camera to an Adobe TIFF file as I was advised that JPEGs lose information each time you open and close the file.
My query is how can a 3mb JPEG turn into a 20mb TIFF, if there is only 3mb
to start with where does the extra 17mb come from?
Cheers
Kevin
Good question 😉
Adobe TIFF? or PSD?
What is the "native" resolution of your camera? L x B in pixels. Each pixel, if 8 bit RGB, has 8 bits of red, 8 bits of green and 8 bits of
blue. 8 bits equals 1 byte. Therefore, each pixel needs to be multiplyed by
3 to display its memory requirements. So, if you have a 6MGPixel camera, the
the pixel dimensions will be 6 MPixels and if each pixel consists of 3 Bytes, your image memory requirements will be a bit less than 18MB, (1Megabyte isn’t 1000 x 1000, it’s 1024 x 1024 or 1.048576MB.which equates
to about 2.86 x pixel dimensions.
Even with a compressed JPG, you can check the actual pixel dimension memory
requirement in Image>Image size. Note how it differs from actual file size.
Opening and closing a JPG doesn’t impair the image quality, it is opening,
manipulating and then resaving the JPG that can cause loss of quality. Each
time the JPG is opened and saved the JPG compression algorythm is applied,
which "throws " pixel data away in reducing file size.
HTH
MH
Good explanation, Mike. I think even I understood it. Thanks —
Bill,
You’re welcome, GTH 😉
I forgot to add, that the pixel dimension size as displayed in Image>Image Size will change as the Image Mode changes, for example, change the mode to 16 bit RGB (2 bytes per pixel) and see the PD double. Convert the image to Grayscale (Only 1 Channel = 1Byte) and see the PD drop to about 95% of the L x B.
The JPG hasn’t got an Image Mode as such, that is provided by the likes of PS. That is why a 2,15MB JPG with a pixel L & B of 3008 x 2000 (6MBPixel camera) has a PD of 17.2 MB in 8 bit RGB and when you save this as a PSD or TIFF the Image Mode used is "embedded" in the file, accounting for the increase in file size.
Regards
Mike H
