Lightroom Classic: PNG export is very slow / CPU heavy

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  • Problem
  • Updated 2 months ago
  • (Edited)
I was very pleased to see export to PNG finally implemented in LR Classic. Unfortunately there appears to be a problem with it. It is *extremely* slow for me when exporting at full size (i.e. not downsized) - taking anything from 20-60 seconds to export just one image. For comparison, exporting the same image as a full-size TIFF takes about 2-3 seconds.

It seems to be slowest when exporting from a jpeg rather than a raw. And for some reason, it's slower exporting an 18MP image than a 24MP one. But either way it always seems to be at least ten times slower than TIFF export.

I have a 4.0GHz i7 iMac with 16GB RAM, so it's no slouch.
I've just upgraded to MacOS 10.14.6 but had the same problem on 10.14.5 too.

Asking around, others report it taking about 16 seconds on Windows - not as slow, but slower than it should be.

I have tried with GPU acceleration enabled and disabled, makes no difference (as expected - it's not using the GPU for this, just caning the CPU).

System Info below:



Lightroom Classic version: 8.4 [ 201908011719-03751b60 ]License: Creative CloudLanguage setting: en-GBOperating system: Mac OS 10Version: 10.14.6 [18G87]Application architecture: x64Logical processor count: 8Processor speed: 4.0 GHzBuilt-in memory: 16,384.0 MBReal memory available to Lightroom: 16,384.0 MBReal memory used by Lightroom: 7,218.7 MB (44.0%)Virtual memory used by Lightroom: 13,317.8 MBMemory cache size: 1,153.4MBInternal Camera Raw version: 11.4 [ 273 ]Maximum thread count used by Camera Raw: 5Camera Raw SIMD optimization: SSE2,AVX,AVX2Camera Raw virtual memory: 1752MB / 8191MB (21%)Camera Raw real memory: 1768MB / 16384MB (10%)Displays: 1) 5120x2880Graphics Processor Info: Metal: AMD Radeon R9 M395Application folder: /Applications/Adobe Lightroom ClassicLibrary Path: /Users/ben/Pictures/Lightroom/Lightroom Catalog-2.lrcatSettings Folder: /Users/ben/Library/Application Support/Adobe/LightroomInstalled Plugins: 1) AdobeStock2) Flickr3) HDR Efex Pro 24) jf Data Explorer5) LensTagger Exif ToolConfig.lua flags: NoneAudioDeviceIOBlockSize: 512AudioDeviceName: Built-in OutputAudioDeviceNumberOfChannels: 2AudioDeviceSampleRate: 44100Build: 12.1x4CoreImage: trueGL_ACCUM_ALPHA_BITS: 0GL_ACCUM_BLUE_BITS: 0GL_ACCUM_GREEN_BITS: 0GL_ACCUM_RED_BITS: 0GL_ALPHA_BITS: 8GL_BLUE_BITS: 8GL_DEPTH_BITS: 24GL_GREEN_BITS: 8GL_MAX_3D_TEXTURE_SIZE: 16384GL_MAX_TEXTURE_SIZE: 16384GL_MAX_TEXTURE_UNITS: 8GL_MAX_VIEWPORT_DIMS: 16384,16384GL_RED_BITS: 8GL_RENDERER: AMD Radeon R9 M395 OpenGL EngineGL_SHADING_LANGUAGE_VERSION: 1.20GL_STENCIL_BITS: 8GL_VENDOR: ATI Technologies Inc.GL_VERSION: 2.1 ATI-2.11.20OGLEnabled: trueGL_EXTENSIONS: GL_ARB_color_buffer_float GL_ARB_depth_buffer_float GL_ARB_depth_clamp GL_ARB_depth_texture GL_ARB_draw_buffers GL_ARB_draw_elements_base_vertex GL_ARB_draw_instanced GL_ARB_fragment_program GL_ARB_fragment_program_shadow GL_ARB_fragment_shader GL_ARB_framebuffer_object GL_ARB_framebuffer_sRGB GL_ARB_half_float_pixel GL_ARB_half_float_vertex GL_ARB_imaging GL_ARB_instanced_arrays GL_ARB_multisample GL_ARB_multitexture GL_ARB_occlusion_query GL_ARB_pixel_buffer_object GL_ARB_point_parameters GL_ARB_point_sprite GL_ARB_provoking_vertex GL_ARB_seamless_cube_map GL_ARB_shader_objects GL_ARB_shader_texture_lod GL_ARB_shading_language_100 GL_ARB_shadow GL_ARB_shadow_ambient GL_ARB_sync GL_ARB_texture_border_clamp GL_ARB_texture_compression GL_ARB_texture_compression_rgtc GL_ARB_texture_cube_map GL_ARB_texture_env_add GL_ARB_texture_env_combine GL_ARB_texture_env_crossbar GL_ARB_texture_env_dot3 GL_ARB_texture_float GL_ARB_texture_mirrored_repeat GL_ARB_texture_non_power_of_two GL_ARB_texture_rectangle GL_ARB_texture_rg GL_ARB_transpose_matrix GL_ARB_vertex_array_bgra GL_ARB_vertex_blend GL_ARB_vertex_buffer_object GL_ARB_vertex_program GL_ARB_vertex_shader GL_ARB_window_pos GL_EXT_abgr GL_EXT_bgra GL_EXT_bindable_uniform GL_EXT_blend_color GL_EXT_blend_equation_separate GL_EXT_blend_func_separate GL_EXT_blend_minmax GL_EXT_blend_subtract GL_EXT_clip_volume_hint GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_depth_bounds_test GL_EXT_draw_buffers2 GL_EXT_draw_range_elements GL_EXT_fog_coord GL_EXT_framebuffer_blit GL_EXT_framebuffer_multisample GL_EXT_framebuffer_object GL_EXT_framebuffer_sRGB GL_EXT_geometry_shader4 GL_EXT_gpu_program_parameters GL_EXT_gpu_shader4 GL_EXT_multi_draw_arrays GL_EXT_packed_depth_stencil GL_EXT_packed_float GL_EXT_provoking_vertex GL_EXT_rescale_normal GL_EXT_secondary_color GL_EXT_separate_specular_color GL_EXT_shadow_funcs GL_EXT_stencil_two_side GL_EXT_stencil_wrap GL_EXT_texture_array GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc GL_EXT_texture_env_add GL_EXT_texture_filter_anisotropic GL_EXT_texture_integer GL_EXT_texture_lod_bias GL_EXT_texture_mirror_clamp GL_EXT_texture_rectangle GL_EXT_texture_shared_exponent GL_EXT_texture_sRGB GL_EXT_texture_sRGB_decode GL_EXT_timer_query GL_EXT_transform_feedback GL_EXT_vertex_array_bgra GL_APPLE_aux_depth_stencil GL_APPLE_client_storage GL_APPLE_element_array GL_APPLE_fence GL_APPLE_float_pixels GL_APPLE_flush_buffer_range GL_APPLE_flush_render GL_APPLE_object_purgeable GL_APPLE_packed_pixels GL_APPLE_pixel_buffer GL_APPLE_rgb_422 GL_APPLE_row_bytes GL_APPLE_specular_vector GL_APPLE_texture_range GL_APPLE_transform_hint GL_APPLE_vertex_array_object GL_APPLE_vertex_array_range GL_APPLE_vertex_point_size GL_APPLE_vertex_program_evaluators GL_APPLE_ycbcr_422 GL_ATI_blend_equation_separate GL_ATI_blend_weighted_minmax GL_ATI_separate_stencil GL_ATI_texture_compression_3dc GL_ATI_texture_env_combine3 GL_ATI_texture_float GL_ATI_texture_mirror_once GL_IBM_rasterpos_clip GL_NV_blend_square GL_NV_conditional_render GL_NV_depth_clamp GL_NV_fog_distance GL_NV_light_max_exponent GL_NV_texgen_reflection GL_NV_texture_barrier GL_SGI_color_matrix GL_SGIS_generate_mipmap GL_SGIS_texture_edge_clamp GL_SGIS_texture_lod 
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Ben Wheeler

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Posted 11 months ago

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Photo of Rikk Flohr

Rikk Flohr, Official Rep

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Ben,

This sounds normal. PNG is a more intensive export process in the Lightroom family of products.  For full res images you are much better off with a TIff as the PNG compression technology is very slow by comparison. 

Do you have a workflow reason for choosing PNG over Tiff for ful-res files?
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Ben Wheeler

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This does not "sound normal" to me. I've never known any other software be so slow to save a PNG. I'm afraid Lightroom's implementation must just be awful.

Yes, I do have a reason for needing PNGs (third party software that will accept PNGs or JPEGs but not TIFFs), so I was very happy that Lightroom finally added it as an option, but it's unusable.

I have resorted to exporting TIFFs and converting to PNGs using ImageMagick, because it's an order of magnitude faster. I can convert 30 images from 8-bit TIFF to PNG in less time than it takes Lightroom to export 3 images as PNG. The final PNGs are the same size. There is clearly something wrong with Lightroom's method.
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Robert Somrak, Champion

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It does seem like there is something wrong with 8 bit PNG export being EXTREMELY slow.

I export 6 RAW files from a Canon 5dmk3 with the following results 

16bit PNG.  27sec
8bit PNG 59 sec
16bit TIFF 11sec
8bit TIFF 11 sec.

There seems to be an issue with the difference between 16 and 8 bit PNG, 


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Robert Somrak, Champion

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I just tried 8 bit PNG and 8 bit TIFF exports from Photoshop and PNG export is at least 6 times slower in Photoshop too.