Thumb and Cache image quality

Hi,
I have the quality for the thumbs and Cache image quality at 100, also have have "Cache as original" but the thumbs and Cache images always lose quality when compared to the album images. I just want them to be resized and not change the quality. How can I do this?

Comments

  • acrylian Administrator

    You did the right way. "Cache as original" refers to keep the same file format, e.g. not caching a png as a smaller jpg.

    If you resize images, it always comes with a certain quality loss as they are most likely are smaller, e.g. loosing resolution. Especially if images are already compressed. The best is to upload uncrompress images (e.g. jpgs with 100% quality).

    Also color profiles may be the reason they look less good. To be an the secure side your images should be sRGB. Although modern browser support profiles graphics library do not always keep them (GD does not if I am not mistaken)
    We have user guide article somewhere about this as well.

    Or are you perhaps accidentally upsaling smaller images in your theme or something?

  • I don't think so, the colors always look for drab for the cached images. For instance, this image: https://www.goodfreephotos.com/united-states/wyoming/yellowstone-national-park/colorful-spring-at-yellowstone-national-park.jpg.php , if you click on the image, you see the full uploaded image and the colors are much better. I just want a resized smaller version of the image in the cache, but it does lose quality.

  • acrylian Administrator

    As mentioned it is the color profile that gets lost. The original has a profile named ProPhoto RGB (which I never heard of) and the resized one has none.

    Which graphics library are you using? GD or Imagick? GD does kill profiles (unless mistaken) while Imagick should try to keep them.

  • I have to use imagick, because GD sometimes makes the VPS crash due to memory constraints.

  • acrylian Administrator

    I will run some local test using Imagick regaridng the profiles. But otherwise consider using sRGB to avoid the issue. Perhaps one of the many web limitation…

  • Yeah, adobe lightroom I think convert to Prophoto RGB as default, so that is why I may have been having issues.

  • acrylian Administrator

    I am not familiar with Lightroom but perhaps you can adjust it somewhere? Independent from that I will take a look about Imagick and profiles. But as you know even correctly kept profiles are no guarantee that it looks the same or good everywhere.

  • It seems to work right after I converted it to sRGB in photoshop. I'm trying to see if there's a version of Imagick that support Prophoto

  • acrylian Administrator

    Is the profile really kept in the resized version? Afterall this color profile converting is kind of a science for itself.

  • JatB Member

    I'll try to shed a little light on this since I've looked into it a bit and work in Lightroom and use Zenphoto. Lightroom works by default in the ProPhoto color space while in the Develop module since it is a very large color space. When you go to export any image, Lightroom asks you to select what kind of color space you want the image to be in under File Settings-Color Space, defaulting on all presets to sRGB, the internet standard.

    If you edit the image outside of Lightroom, from Lightroom, say in Photoshop, it can assign the ProPhoto color space to the image. To change that in Lightroom, go to Preferences-External Editing (or you can always convert it in your external program after editing).

    As mentioned, the default GD image processor will drop the color profile from images, so thumbnails from original images in a different color space from sRGB will look incorrect, as all images without a color profile are assumed by the spec to be in sRGB.

    If you change to Imagick (using ImageMagick), it will embed the correct color space, but beware, this can cause thumbnails to balloon in size 10x-60x, depending on what color profile you are using.

    The other thing to consider with the ProPhoto color space, is that no monitor can fully display the colors. Many monitors out there even have issues displaying 100% of sRGB. High-end wide gamut monitors meant for color editing should support 100% AdobeRGB, but very few people have them. Some really high-end monitors are starting to add support for the even larger P3 standard.

    That said, almost no one will be using a hardware calibrated monitor with browsers setup to properly display your images. It has only been recently that browsers have gained support for color profiles, and properly supported them. I still have issues with Firefox that needs some manual configs added to it for it to work right.

    Read here if you want some more info about the subject or to test your browser's color setup-
    https://cameratico.com/guides/web-browser-color-management-guide/

    My advice is to export to sRGB. If you want to future-proof it a little or are aiming for newer devices, try exporting to AdobeRGB.

    Hope that helps.

  • acrylian Administrator

    @jatb Thanks, that's a good roundup! Meanwhile I looked up our much shorter user guide notice about this: https://www.zenphoto.org/news/problems-with-albums-and-images/#--images-have-wrong-colors

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