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by garik

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52

The JPEG format has the advantage of giving small files. The RAW formats have the advantage of preserving all the data collected at the shot. The PNG format gives neither of these advantages, so you don't even get a compromise between the other formats, you get almost only the drawbacks from both formats.


46

If the dimensions of the image are multiples of 8 (or 16 if chroma subsampling is used) then the rotations are lossless. Otherwise it is not possible to rotate the image without recomputing the blocks i.e. recompressing the image, which is lossy. The reason for this is that jpeg images are broken up into a series of 8x8 or 16x16 blocks which are compressed ...


39

Image size notes aside, a big reason is that PNG does not have a standardized means of EXIF embedding and that will immediately shy the camera makers away from it. There would be a lot of information lost by doing image conversion to PNG in camera as a result and, for the most part, would probably been seen as a negative by most photographers.


24

PNG may use a lossless compression algorithm, but it is lossy in comparison to the raw data. You lose bit depth, the camera may introduce demosaicing artifacts, you may bake in a bad color balance, the camera may apply inappropriate sharpening, the in-camera noise reduction may wash out detail, etc. I don't think there's a big demand for a format that's as ...


23

Photoshop + Layers FTW. (yes, you can also use the Gimp, or any other editing software with the same functions.) Start with your base image, in the case above, I used the jpeg quality 100 image. create a new layer atop it paste the second image into that layer set the layer style to "difference" create an effect layer atop that set the effect to threshold ...


21

I think you're going about this the wrong way. If you have 2GB of images at 4-5MB each, that's somewhere between 400 and 500 images. That's way too many. Even your close friends probably don't want to wade through all of that. Instead, go through and pick out the very best 10%. Or 5% or even 1%. Take some care and write a meaningful caption for each one. An ...


17

JPEG 2000 has not garnered wide acceptance due to a few factors. Lacking backwards compatibility to JPEG Lack of wide browser support Questionable legal status (Only) 20% higher performance, while considering how inexpensive storage is Additional processing power/time needed to create JPEG already considered quite good Amount of rework to the code in ...


16

Raw files are an intermediate format. It's essentially the unmodified sensor data (often in Bayer pattern), packaged with a bunch of metadata about the shot as well as a JPEG preview (for quick viewing). The data is both losslessly compressed and of a higher bit depth than that of JPEG. You only need to shoot raw if you wish to develop the photos into ...


14

JPEG actually uses two types of compression, a lossly and a lossless one. Lossless compression doesn't cause artifacts, so we can ignore that part. The particular type of lossy compression in JPEG, called a discrete cosine transform for the math knurds, allows a tradeoff between compression ratio and fidelity. Most software sufaces this as a "quality" ...


13

An example Using the current photo of the week image. This is the high-quality JPEG: re-saved in Gimp with JPEG quality 80 (low); please note the general loss of sharpness, "dots" around high-contrast edges, loss of detail in low-contrast areas: and re-saved in GIMP with JPEG quality 30 (very low); please note evident 8x8 blocks and severe loss of ...


12

If you save a JPEG image with an extremely low quality level, you WILL get compression artifacts. Its just a simple fact of JPEG lossy compression. If you wish to avoid compression artifacts, use a higher quality setting than 2. You won't need to save at maximum quality, as most images can be saved with a fairly low quality setting without noticeable loss in ...


12

If you upload a JPEG, Flickr does not modify the Original-size image in any way, apart from changing the filename. I tested it out by uploading a full-size, 100% quality JPEG to Flickr then re-downloading the Original size image and comparing it with the original (using a comparison tool called Beyond Compare). The two files are identical, byte for byte. ...


12

The first two images both have embedded color profiles. The smaller one has Adobe RGB, and the larger one has "TIFF RGB", which happens to consume more space. My guess is you probably want these to be sRGB anyway, with no embedded color profile. In the second case, it's the details. The hand photograph has big areas of the same color, a lot of blur, and ...


11

If you use Photoshop, here's how I'd do it: Put the two jpegs in the same psd file, in two separate layers. They should overlap exactly, since their dimensions are the same. (which one goes on top doesn't matter). Set the layer blending mode to "Difference." You'd see a mostly black result. Depends on the quality difference between the two original layers ...


11

The image will be recompressed. The two scenarios you describe are actually effectively the same, because the lossy part of the JPEG compression discards information which stays gone when the image is decompressed. (Hence, lossy.) That means that reapplying with the exact same parameters shouldn't do much, either in terms of further space saves or in terms ...


10

Setting a minimum filesize whilst fixing the image width and height is silly. If you don't use compression then the filesize is determined by the image dimensions. And if you do use compression then the filesize is determined by the level of entropy (disorder) in the image. Some images have higher entropy because there is more going on, more detail etc. in ...


9

Better is a relative term and, to some degree, will vary in terms of amount between the two depending on a variety of factors including the bit-depth, frequency of discrete colours, etc. Some experimentation may be necessary on this front, though my reading indicates LZW is good for lower bit-depth images with lots of the same colours and tones in it and ZIP ...


9

JPG compression is done in blocks of pixels. In a highly compressed JPG image the edges of those blocks can be seen: in the original image two pixels may have been very close in brightness and color, but if they are in different blocks, then after compression and decompression (when viewed) each of their values may differ from the original, so you lose ...


9

You are correct that once you compress, there is no going back. The best way I would consider compression is to actually delete images which are low quality, uninteresting and near duplicates, rather than systematically reducing quality globally. This is probably not the question you were asking though :) The level of tolerable compression is mostly ...


9

Uncompressed RGB files (3 values per pixel) will be larger than your raws, as the raws contain a monochrome bitmap (1 value per pixel), and usually a downscaled, aggressively compressed preview that takes a fraction of the size, 400k for Canon 10MP cameras, and 1M for Nikon D5100 (I know these numbers because I used to read them out of the raw files and ...


8

If you are saving to JPEG after processing check your compression settings. File size can climb astonishingly high the closer you get to 100% quality without any noticeable difference in quality. Dropping it down to around 90% can cut file size quite a bit.


8

As is often the case, "there is no free lunch". JPEG is the de-facto standard image format, and uses lossy compression. That means that to get smaller file sizes, you will lose image quality. The only question is how much you lose, and whether that loss is acceptable. That said, there are lossless compression techniques that are used by other formats ...


8

Disks are still pretty cheap these days so there are advantages to JPEG files, even if they are as big as the original RAW, instant image preview, being able to display on computers without RAW software. The "quality" parameter determines the quantization matrix used to compress the data. Without going into too much detail this determines the degree to ...


8

To be frank, it is entirely anecdotal that a JPEG image should be exported at a certain compression level all the time. The amount of JPEG compression should really depend on the usage purpose for the JPEG, and the contents of the JPEG. The quality level one should choose when exporting an image to JPEG is highly dependent upon the kind of detail contained ...


8

There are a few tricks that can help, but you'll never get the same quality out of facebook as you would from a site that allows larger files without compressing them so aggressively. Here's a link to a facebook help page that describes some of the issues. Expand the section titled "How can I make sure that my photos display in the highest possible ...


7

Because people who really care a lot about quality generally just use raw files. JPEG 2000 is quite a bit of extra work to implement, for what is apparently perceived as a fairly minimal benefit in quality.


6

In a normal RAW image, the data is stored as linear values. However, this is very inefficient. We don't see light linearly, which is why gamma correction is needed from the RAW values to get the values you would output to a raster image, or to screen, etc. Vast amounts of values are allocated to the lightest areas where, after gamma correction, most ...


6

With any improved image format, there's a chicken and egg problem. A format isn't useful unless people can see it, and if there's not widespread display medium support, it's hard to get started. If you look at Wikipedia's list of applications with JPEG 2000 support, you'll notice that major web browser support is weak at best. Same goes for digital picture ...


6

Yes. How else could it be displayed? The screen needs to show the actual pixels, not an abstracted mathematical representation of them. Perhaps more crucially, a JPEG needs to be converted to a bitmap to be edited, which is why re-saving an image in JPEG can cause artifacts and loss of detail even if you don't change anything.



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