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gordonr

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Posts posted by gordonr

    Curves and Levels (Difference?)

    in The Digital Darkroom: Process, Technique & Printing

    Posted

    The most fundamental point (in addition to those listed above) is that levels uses a single curve function called <a href="http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html">Gamma</a> (http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html), which closely approximates the logarithmic human visual system, as well as the phosphors in computer monitor CRTs.

    <p>

    Curves allows you to choose any function, which might better approximate parts of the image needing adjustment, but which might also produce unrealistic tones and posterisation, if not carefully used.

    Cluster size in Windows

    in The Digital Darkroom: Process, Technique & Printing

    Posted

    Cluster size is directly relevant to the total size of the FAT (File Allocation Table), and inversely proportional to the amount of overhead processing involved in file I/O (fragmented files). However, with today's CPUs and RAM available, cluster size is unlikely to have any performance effects.

     

    If you make the cluster size too large and have many hundreds of thousands of files, you may run out of clusters before the disk is full, because of the wasted space.

     

    Cluster size has no effect on the underlying hardware, and the biggest effects of disk performance is latency (the time taken for one rotation of the disk, i.e. RPM), and track-to-track seek-times.

    Major trouble posting to my gallery

    in PhotoNet Site Help

    Posted

    Photo.net has always recompressed images (see many previous threads). The issue with your flower photo is with 2X2 chroma subsampling (pink/red is particularly noticeable), not recompression itself.

    <p>

    This problem has occured since the major server upgrade in March (I have pointed this out to Brian M.) For more information see my article on <a href="http://www.photo.net/learn/jpeg/">Jpeg Compression</a> (http://www.photo.net/learn/jpeg/).

    <p>

    Here is an example of what you image would look like if the chroma subsampling issue were fixed (36KB). There is no visible difference from the original (116KB) IMHO.

    Poor reproduction of reds on photo.net.

    in PhotoNet Site Help

    Posted

    There have been several complaints about photo.net Jpeg compression, particularly since the last server upgrade in March. It seems the new server uses 2X1 chroma subsampling (averaging) when recompressing images. The human eye is quite sensitive to red, and this loss of saturation in certain images is certainly noticeable.

    <p>

    Using 2X1 subsampling makes colour Jpeg files up to 30% smaller (depending on image content), so there may be a good reason for this.

    I have mentioned this several times to Brian M, but I think he had other priorities. Sorry I didn't see this thread earlier.

    <p>

    See my article on <a href="http://www.photo.net/learn/jpeg/">Jpeg Compression</a> (http://www.photo.net/learn/jpeg/).

    PHOTO.NET caching question

    in PhotoNet Site Help

    Posted

    You can manually tidy up the cache without resorting to deleting it all, but this can be tedious. All the pop-ups, banners, and other trash that most sites are loaded with, will fill op your cache quickly (these can certainly be deleted). Increase the size-limit as large as feasible, but note that early versions of IE (up to 5.0) only calculated based on 2GB hard drive capacity...

    Getting scans from a photo lab vs film scanner

    in The Digital Darkroom: Process, Technique & Printing

    Posted

    Find a lab with a Sony UY series 35mm Film Scanner, and ask them to use the high resolution setting. These can scan 1100dpi in 6 sec, and 2200dpi in 9 sec. This may cost slightly more, but the largest cost is film handling time, not scanning time.

     

    Mine was less than $1 for a cut strip of 4 negatives (better if the whole roll is uncut). This is not as high quality as the top-end scanners, but certainly adequate for most purposes.

    Whats wrong?

    in PhotoNet Site Help

    Posted

    Can the original poster please let us know if anything has helped? Alternatively, can you post the original image as an attachment to this thread. (Attachments are NOT recompressed, unlike gallery photos).

    Whats wrong?

    in PhotoNet Site Help

    Posted

    With all due respect, most of the information above is misleading. I wrote a lengthy article on <a href="http://www.photo.net/learn/jpeg/">Jpeg Compression</a> (http://www.photo.net/learn/jpeg/) which explains your problem.

    <p>

    Your Jpeg (currently) in the database has a chroma subsampling of 2X2. That means that highly saturated areas of colour tend to smear out, and produce the most objectionable aretefacts. I have seen plenty of examples of highly saturated images such as yours with the same problem.

    <p>

    Try resaving the original image at the highest possible quality setting, and see if that improves it when uploading. Photo.net should recompress and use 1X1 chroma subsampling.

    <p>

    It is most likely that your photo editor has done the 2X2 subsampling (either Photoshop at a low quality setting, or another image editor which always uses 2X2 subsampling).

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