73

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-...


49

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 ...


29

In general, photos at lower ISOs will have less noise. This means that they compress better (remember that RAW files have lossless compression) and so, on average, you'll be able to fit more images onto the card. The other important thing to remember is that the number shown is only an estimate - how many images actually fit depends on what you take photos ...


18

The reason you got confused is that it's not the file size that is displayed in Photoshop. Photoshop's status bar shows uncompressed size of image. With three 8-bit color channels, that's 3 bytes per pixel, resulting 34.9 MB for a 4288 x 2848 image from your camera. JPEG is a compressed format, so the actual file is smaller. Showing compressed size would ...


18

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

File size, quality, resolution - pick any two. If you had images in an uncompressed format like BMP, then you could make them a bit smaller without sacrificing any quality or resolution by saving them in a compressed format that doesn't do lossy compression, like PNG-24. JPEG images are already compressed, so with the given quality and resultion they are ...


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

Did you use the CF card in your computer and either store non-picture files on it, or delete the files without emptying the trash / recycle bin when you were done? A bunch of hidden files can fill up the card's space pretty quickly (happened to me a couple weekends ago; luckily I always carry a spare). It could also be a corrupted card, and some sectors ...


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

I would say TIFF is probably the best format. JPEG 2000, like JPEG, is still a lossy compressed format when you really try to save space (the lossless version can compress a bit, but not nearly as much as the lossy form, and some forms of the "lossless" wavelet compression still can't fully reproduce the exact original image.) When scanning in an original ...


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

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

No, it doesn't work that way. The image file isn't built up as the exposure goes on, but rather is made from a full read of the sensor when the exposure is complete. So, you're not writing more data to the memory card when you expose for a longer time. Each photosite — one "pixel" on the sensor — is a counter that goes up as it's hit by more photons. It's ...


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 ...


9

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 ...


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

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

It sounds like she's saving uncompressed TIFs. Ps will give you various options such as LZW or ZIP compression when you save. Since TIFF is lossless you can safely choose any of them. JPEG is not a good alternative as it is lossy; you will lose image quality.


7

Two images with the same dimensions contain the same amount of data but not necessarily the same amount of information. A pure white image contains virtually no information and can be compressed into a very small space (it is sufficient to store only the height and width in order to fully recreate this image). Scenes with a lot of detail contain a lot of ...


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

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

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 ...


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

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 ...


5

PNG compression quality varies greatly from compressor to compressor. The standard PNG compression in Photoshop for example can sometimes commonly be beat by large percentage points. This is primarily due to more intelligent switching algorithms when it picks the kind of prediction to do for a certain set of pixels. Most of the "additional" compression is ...


Only top voted, non community-wiki answers of a minimum length are eligible