resampling help needed - DPChallenge Forums

12/06/2005 09:36:58 PM · #1

Hi EVeryone,

I just can't get the system of resampling to a 48 MB size file as discussed on another thread - even when I put the pixel size to a really large amount (for example 13,000 x 9000) I still get a size of about 8 MB. Am I reading something wrong? These files are taking forever to save, edit etc. could it be I did upsize them to that large of a file? I am using Photoshop Elements, resample. Also, using bicubic smoother it still seems to have lost quite a bit of quality at 100% (even after sharpening, reducing noise) - is this correct as well, or should it still look good? Would also like to eventually submit to larger stock sites, so that's why I am trying this. Thanks in advance for any help. PS, my last attemp I changed to percent and hit 400 - is this correct?

12/06/2005 09:47:52 PM · #2

We need to know the size, in pixels, of the original.

R.

Sigma 105mm f/2.8 EX DG Macro for Canon

12/06/2005 10:07:02 PM · #3

Thanks,

The one I was playing around with was originally 3,456 x 2,304 pixels, 2.37 MB, at 72 dpi (I changed to 300 dpi before resizing), bit depth 24, taken with a canon rebel xt. After resizing: 13,824 x 9,216 pixels, 8.08 MB, 300 dpi.

Does this sound right to you?

longlivenyhc

Canon EOS-300D Rebel

12/06/2005 10:10:52 PM · #4

saving it as a tiff?

12/06/2005 10:12:15 PM · #5

..no....I was saving them as jpeg hi quality....is that what I am doing wrong??

12/06/2005 10:17:40 PM · #6

welll...

first, the dpi is irrelevant to the image size; it's just "printing instructions". Regardless of the dpi you specify, the pixel count on a given image is the same; the dpi just tells the printer how to space them out. So to speak.

Second, you're apparently doing this with jpg files? At what quality level? When I make RAW files with my 20D (roughly the same sensor as yours) they are nearly 9Mb in size. If you really NEED images that big, you better start working with RAW and use no compression at all.

Third, extreme upsampling in jpg often doesn't increase size that much at all, because the neighboring pixels in the upsample are duplicates of the existing pixels, so they don't add hardly anyuthing to the compressed dimensions of the image. To see what I mean in a native condition, shoot a black something-or-other and a very detailed something-else at the same jpg quality level and compare the file sizes. The black file will be MUCH smaller because everything compresses to a single value.

Robt.

Message edited by author 2005-12-06 22:19:52.

12/06/2005 10:19:24 PM · #7

Originally posted by BJ:

..no....I was saving them as jpeg hi quality....is that what I am doing wrong??

That's definitely part of the problem. You want to do all your work in an uncompressed format, .psd actually will be best. And you want to shoot in RAW if you can, so there's no compression whatsoever on the original image.

R.

12/06/2005 10:39:28 PM · #8

Thanks Bear music & longlivenyhc!!

I understand so much better now. I will start trying to shoot in RAW (haven't yet) or save as TIFF or PSD right away before resampling. (I just redid my photo but didn't save to TIFF first and ended up with 386MB file, lol!!).

Thanks again, this was driving me crazy. I also alway wondered why the file sizes were different to begin with when the settings were the same, now I understand that it depends on the initial compression:)

bj

Message edited by author 2005-12-06 22:59:35.

Prof_Fate

12/06/2005 11:49:13 PM · #9

I have a rebel, and a CRW (raw) file on disk is about 5Mb (varies based on file contents. I see 4.8 to 5.8mb in my one directory. the variation may be form RAW adjustments done in DPP).

JPGs (large fine) are 2.4 Mb or so, again, some variance.

If i open the jpg in PS, and save as a TIF (no other work) i get an 18Mb file. (this is an 8 bit file)

If i convert the RAW file to TIF 16 bit in DPP and save that i get a 36Mb file.