Hi All,

I started another thread on this some time back but as there are things I still don't understand I am hoping some one here may know the answer.

On the Alamny site it states

 

Note for images from digital cameras - We strongly recommend that images are captured on a digital camera capable of producing files of 17MB and upwards (6 megapixels). Please then interpolate the images to a minimum of 48MB using professional upsizing software.

This is the link if anyone needs it

http://www.alamy.com/contributors/stock-photography-technical-criteria.asp

 

I have a Nikon D100 which is 6 megapixels.If I shoot in RAW I get a 10 MB file per image.

Alamy states that the image should be saved as a jpeg file

I open the image in Photoshop CS2 and save the image as a jpeg and I end up with a 2.5 MB file.

Even using Genuine fractals 4.1 ( if I had it ) it will only up size the image by 800% without loss of quality ( They say it does ) so that gives me a 20 MB file,way short of what they require.

 

So how would one shoot a 17 MB file on a 6 megapixel camera.Do some 6 megapixel cameras acheive this.

Do I need a new camera :-( 

 

Maybe there is a simple answer to all this - sorry for being thick.

Any help greatly appreciated.

 

Eddie

The file size of 48MB they refer to is the size that is circled in my example. If you are in doubt if that is the correct file size, click on the little arrow to the right of these numbers... you'll see a drop down menu where you can choose "Show..." and then you'll see, among others, "Document Sizes". That is the correct uncompressed file size they refer to. Beware, if you are using multiple layers in your image, the second number shows the multiple layered file size.

Hi girsempa,
Thanks for the help - another question.
I followed your instructions and I opened a jpeg in CS2 and it shows the the document size as 17.2M  If so that explains them saying a 6 megapixel gives a file of 17 MB.
When I look at  the file size in my folder says 2.6 MB,is that because the file gets compressed or something when saved to the hard drive.
Thanks a million for your help so far
Eddie

Yes Eddie, the JPEG compression makes the file size on your hard disk much smaller, but when you open it in Photoshop, the document size in Photoshop will still be the same large size. Just try this: if you save the image as a TIFF file, and you choose Image Compression "NONE", you'll see that the file size of your saved image on your hard disk will be approximately the same (uncompressed) size as in your Photoshop document. That is because 'uncompressed TIFF' is a 'lossless' image format, whereas JPEG is a 'lossy' image format, that is, it looses image information when saved as JPEG. That's why Alamy asks you to save your image at the highest quality JPEG compression (10 or more), otherwise it will loose too much image information. I hope this explanation is useful and not too 'blurry' ;o)) Remember you can always ask away.... __/ Geert

@ejn...You said**...."****So how would one shoot a 17 MB file on a 6 megapixel camera."
**

This is from one of my posts here before...perhaps it will help you in understanding how a 6MP D100 can produce 17MB files....

"JPEG images only support 24 bits per pixel...8 bits for each of the red, green and blue channels....ie an 8bit image. Most consumer digicams have an onboard 8 bit D/A converter...resulting in the what we call 8 bit JPEG.
DSLR's on the other hand are able to capture a greater dynamic range because of the larger sensor size...so, they come with 10 or 12 bit A/D converters...allowing you to save in the RAW format.
Further;
8 bits = 256 levels of brightness per color channel
10 bits = 1024 levels of brightness per color channel
12 bits = 4096 levels of brightness per color channel

So, now if we take a 3008X2000 pixel image out of a Nikon D70, we get;

3008 X 2000 = 6016000 pixels

For a JPEG image there are 8 bits for each of the 3 channels per pixel...so 24 bits per pixel.

That give us...6016000 X 24 = 144384000 bits in total for that JPEG image.

Now remember that one BYTE = 8 bits....so 144384000/8 = 18048000 BYTES

Now remember that one MEGABYTE = 1048576 BYTES...so...

18048000/1048576 = 17.2 MEGABYTES!

If you open ANY 3008 X 2000 JPEG image in PS, it's actual size can be read at the bottom of the screen....it is exactly 17.2MB!!!!!

Now, to a TIFF image....a 16 bit TIFF image stores 16bits for each channel per pixel = 48 bits per pixel.

Which is exactly double the 24 from the JPEG example above...so, it would be approx 34 MB.

Do the math for your pixel count out of your cam....it should roughly match the image size numbers seen at the bottom of your PS screen