Reduction in file sizes 2.5MB to less than 1MB

[michael_chia1]

I just purchased a Nikon D70 and am quite pleased with it. I shoot

at at JPEG, Large, Fine which produces a file size of approximately

2.5MB. When I transfer it to my pc, it still remains 2.5MB.

However, when I open it in Photoshop, it is less than the original

2.5MB. Worse, after working and saving it, it comes down to just

under 1MB.

 

What happened? Is there something wrong I did? Or do I need

Captureware to keep the file size as they are. Have I lost any

information due to the smaller file size?

 

Can anyone help?

 

Thanks

Michael

[daveswitzer]

Likely it is re-saving the JPG (or should I say, re-compressing) in a more agressive fashion that the camera saved it as.

 

Check your settings on saving and crank 'em up full blast.. or better yet open the JPG's and save 'em as PSDs while you edit + keep them, then save down to JPG's if you ever require them (For putting online, submitting to get printed, etc)

[jon_austin]

The most obvious answer is that when you (re-)save the image, your quality (compression) level in Photoshop for saving JPEGs is more aggressive than that in your D70. Once that information is thrown away, it's gone. Try bumping up your quality level a bit (I use 10), and see what the result is.

 

Also, always work on a COPY of your JPEG image; never the original. That way, you can always retrieve a new copy of the original, as needed. And when working with a JPEG image, don't open and save it more than once. Every time you do this, you throw away more image data.

[jbs]

What I do....

 

Download jpg, burn copy...open jpg in PS work it save it as tiff, burn tiff copy. In this way I keep the original and the uncompressed edited finalized file without loss of info...Remember NEVER re-compress a compression....;)...J

[michael_chia]

Thanks for the responses. This actually what is happening.

 

I transfer the file still as jpeg at 2.5MB. In PS it opens it at 17MB !!!! After working on it if I save it as jpeg, it drops to less than 1MB!

 

But if I save it as tif, it remains at 17MB. Where did all the extra KB from?

 

Any ideas?

Thanks!

Michael

[maxz]

<BLOCKQUOTE><I>I transfer the file still as jpeg at 2.5MB. In PS it opens it at 17MB !!!! After working on it if I save it as jpeg, it drops to less than 1MB!<P>But if I save it as tif, it remains at 17MB. Where did all the extra KB from?</I></BLOCKQUOTE>

<P>It comes from simple math. An image from the D70s sensor of 3008x2000 pixels are 6016000 pixels. When an image is stored as RGB you need one byte per color and pixel, so 6016000 times 3 is 18048000 bytes (1 Mbyte = 1024*1024 bytes gives 17.21 Mbytes).</P>

<P>When you save something as jpeg, data is thrown away. But that data is data which you probably wouldn't see anyway. Instead it is filled with data that, together with the rest of the image data, compresses really well. Compression rations of 1:10 is very common and usually gives good results. The actual compression ration depends upon the image itself and how much you tell the compression algorithm to reduce the file size. Typical size of an 17-18Mbyte image would probably be between 1 and 3 Mbytes. Mind though, that repeted recompression of jpeg will eventually degenerate the image.</P>

<P>So, when PhotoShop keeps the image in memory for editing it is a raw bitmap, that is you have to use roughly 17 Mbyte. Uncompressed tiff are just the same.</P>

[gordonr]

My article on photo.net answers some of your questions: <a href="http://www.photo.net/learn/jpeg/">Jpeg Compression</a> (http://www.photo.net/learn/jpeg/)