74

Sorry, but your basic premise is wrong: an image can be encoded as an array of RBG pixels with 8 bits per value, but there are a lot of other ways: one channel with one bit/channel (pure black and white), one channel with x bit/channel (grayscale formats, x will usually be 8 or 16, giving 256 or 65536 values), various palette-based formats (cf.GIF) full-...


50

If at the core, photos are just 3 channels of pixel values [0, 255] X RBG, But photos are not "just 3 channels of pixel values" even "at the core." Computer screens are typically made up of an array of RGB pixels, so if you want to display an image on a computer screen you must, at some point, map whatever image data you have into an array of RGB pixels, ...


30

The size of files compressed with JPEG vary depending on the complexity of the image. Trying the control the file sizes the way you describe will result in highly variable perceived image quality. Consider the following options instead: The good-enough approach. Use a quality setting that you find acceptable, like 75. Compare the size of the result with ...


19

In addition to @remco's fantastic answer, I want to add why there are different codecs for (roughly) the same purpose. Codecs are designed to: Be lossless vs. lossy Encode fast vs. reduce filesize Asymmetric vs. Symmetric en-/decoding Be compatible with software Be perceptionally almost lossless in different compression levels / situations Have features ...


18

No. This is a wrong approach. File size in pixels, yes, has something to do with the final weight, but it is not the only factor. Make a test. Take a completely white file of the same 2400x600px, and save it as JPG. Now take a photo of a forest (same 2400x600px) with lots of details and save it. This file will be larger using the same compression settings....


17

JPEG is an image format with lossy compression. This means, every time you save a modified JPEG image, its quality gets slightly reduced because the algorithms used for encoding and compressing the information (namely DCT - discrete cosine transform) do not work pixel-perfect but only store the most important (depending on the quality/compression level) ...


14

To simplify a bit, JPEG image compression splits the image into different frequency components and stores them separately. Depending on the compression settings, it also stores the higher frequency components with less precision, since any round-off errors in those components are less visible to the human eye. After rounding off the data, it then applies a ...


12

There are several reasons why this assumption is incorrect, and they all come down to one thing: What scale are you actually using? And that can be broken down a little further: What is 255? "Color" is not a property of the physical universe. It is a sensation that arises in the mind. And, that includes things like "blue", "green", and "red". A scale ...


11

TIFF is a container format which supports a collection of other standards and like any container what's in it will be entirely down to what you (or whoever wrote the TIFF export you're using) has decided to put in it. At a guess from the file size your converter has gone to 16bpc/RGB uncompressed. If so then that file size looks about right. If it is ...


10

This is not only possible, but extremely likely, when you're using a compressed image format such as JPEG. Data compression methods in general become more efficient as the data to be compressed decreases in entropy (try creating zip files of a large page of actual text vs. the same sized page of a single repeated character). The more features or fine ...


10

If at the core, photos are just 3 channels of pixel values [0, 255] X RBG That is a seriously broken assumption and the rest of your question is simply not answerable without breaking away from it. I mean, what makes a RAW different than a TIFF -- aren't these all limited to values between 0 - 255? The term "raw" can refer to two different things, a "...


10

Web developer here. Here's how I'd approach this: 1. Determine the displayed image dimensions and required screen resolutions. Your first task is determining what pixel sizes the images will be displayed at. Are they product photos in an online store? A photo gallery? User profile photos? Multiple different sizes? Make a list of the pixel dimensions you'll ...


8

An image doesn't have a DPI until you print it. All it has are dimensions in pixels. Anything else is simply an interpolation of one system to another in order to display on your screen... which is probably about 72dpi anyway. If your image is 6000 x 4000 pixels, then that's its size, whatever dpi you think you may have saved it at.


8

No, an image is not just RGB values in the range 0-255. Even if you ignore storage formats, there are many ways to describe color. Here are some examples: Red, green and blue components (RGB) Cyan, magenta, yellow and black components (CMYK) Hue, saturation and lightness/value (HSL/HSV) The amount of light that hit a group of sensors in a camera The amount ...


7

JPEG is a lossy format and it has variable quality levels which result in larger or smaller file sizes. Whenever you save a file in a lossy format, additional detail is lost, so even though you saved the finished version as a higher quality JPEG, it is still actually lower quality than the original was, despite the growth in the file size. It is still ...


7

Even if you knew the exact amount of free space remaining on your memory card you could still only guess the approximate number of remaining frames you could add to the card. It is, in fact, exactly what your camera is already doing for you. This is because even RAW files are compressed, albeit losslessly, and so the exact size of a file depends upon the ...


7

The "ImageOptim" tool pulls together a bunch of other things, and in the case of JPEG files, the relevant thing is the MozJPEG optimizing encoder. If you use this encoder and then resize and save with a different encoder, you will lose the benefit. Saving with the optimizer needs to be the last step. Also worth noting: if you're starting with a JPEG and ...


6

To a very large extent, pixels don't matter - or at the very least, more pixels won't make things significantly worse. What does matter is the size of the sensor in each camera - the EOS 600D has an APS-C sized sensor with a total area of around 330 mm^2, while the Note 3 has a 1/3.2" sensor with a total area of around 16 mm^2 - or in other words, about 5% ...


6

Select the RAW photos, then do an Export. In the Export Location section, choose Export To: Same folder as original photo. Check the Add to This Catalog Checkbox. Select the file output options you want for the new images. Export the images. At this point the JPG's will be imported into the same folder, and your RAW files should still be selected, ...


6

While @Rafael's answer has explained the JPEG compression ins and out, I will try to answer your web and upload problematic. Using an image in a website (for design or content) will dictate some imperatives : what my image will be used for ? Logo, cover photo, thumbnail, photo in a blog post, fullscreen photo for a gallery... Also, if you use it for ...


6

None of 1-4 matter. All the major social networks (definitely including Facebook, Twitter and Instagram) re-encode any uploaded photos with their own settings, optimised for their use case (reducing file size/bandwidth) rather than yours. Obviously they can't re-add quality that wasn't there, but they can and will remove any carefully optimised settings you ...


5

JPEG file size is a meaningless measure, except as an optimization criterion for bandwith/diskspace considerations. Since JPEG is optimized to compress areas with little detail, while preserving fine detail, compression is dependent on the details in the image. There is no way you could produce a 20mb file from eg. a plain white image, no matter the ...


5

The comments have really answered the question here: The behaviour you're seeing is as you should expect. The settings for adjustment layers alone have no equivalence in any of the TIFF content standards. TIFF does allow for vendor specific extensions and this would be an example of one but saving to a nonstandard TIFF would be pointless if nobody could ...


5

On the export dialog, set your image sizing (I set mine as you requested). Then click the add button in the bottom left hand corner of the dialog. Set its name And you are all set.


5

An expert said I should use at least 24MB pictures for stock. You sure the "expert" meant 24 MB, not MP? I don't know much about the higher MP cameras, but I can't imagine anything but maybe the 36 MP Nikon D800 having a 24MB file size. If you take a look at Nikon's official website, you'll see file-sizes ranging from 17 to 29 MB. If it's true that you are ...


5

It is possible and even trivial but I am not aware of any application to do that task specifically. There reason why the file size changes when rotated is that TIFF files are encoded losslessly as one would compress a stream of pixels components from one corner of the image to the opposite one. If you consider Run-Length-Encoding (RLE) which a common TIFF ...


5

Your premise is not wrong: any image can be represented using an N-dimensional array of finite values. Personally, I generalize that using discrete geometry instead of a matrix, but the essence is the same. But that's the content, not the file. However, the file formats are different. Basically, there are several different ways to represent that same image, ...


4

The main difference I see is that they're saved with different JPEG quality parameters - the smaller file has quality 91 (according to GIMP), whereas the larger file has quality 99. File size can grow pretty exponentially at high quality parameters. Resaving the larger file at quality 91 reduces it to around 2.2 Mb, which while still significantly bigger ...


4

When you open a JPEG file that was originally saved to a given quality, it will be decoded and decompressed to a certain image in Photoshop. That becomes the new "original" when you save the second time. When you save that image at 100% quality Photoshop tries to preserve whatever image it is as close as possible. You aren't getting the quality of the ...


4

JPG is a compressed, lossy file format, but it is not magic! 940 x 885 pixles in 8-bit RGB color means that the uncompressed image is about 940 x 885 x 3 bytes = ca 2.5 megabytes. You are trying to compress this to 20 kilobytes, which means that you are looking for more than a 1000:1 compression rate. This is just not going to happen unless the image file is ...


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